Rabbits

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Rabbits are small mammals in the family Leporidae of the order Lagomorpha (along with the hare and the pika). Oryctolagus cuniculus includes the European rabbit species and its descendants, the world’s 305 breeds[1] of domestic rabbitSylvilagus includes thirteen wild rabbit species, among them the seven types of cottontail. The European rabbit, which has been introduced on every continent except Antarctica, is familiar throughout the world as a wild prey animal and as a domesticated form of livestock and pet. With its widespread effect on ecologies and cultures, the rabbit (or bunny) is, in many areas of the world, a part of daily life—as food, clothing, and companion, and as a source of artistic inspiration.

Male rabbits are called bucks; females are called does. An older term for an adult rabbit is coney, while rabbit once referred only to the young animals. Another term for a young rabbit is bunny, though this term is often applied informally (especially by children) to rabbits generally, especially domestic ones. More recently, the term kit or kitten has been used to refer to a young rabbit.

A group of rabbits is known as a colony or nest (or, occasionally, a warren, though this more commonly refers to where the rabbits live). A group of baby rabbits produced from a single mating is referred to as a litter, and a group of domestic rabbits living together is sometimes called a herd

Rabbits and hares were formerly classified in the order Rodentia (rodent) until 1912, when they were moved into a new order, Lagomorpha (which also includes pikas). Below are some of the genera and species of the rabbit

Hares are precocial, born relatively mature and mobile with hair and good vision, while rabbits are altricial, born hairless and blind, and requiring closer care. Hares (and cottontail rabbits) live a relatively solitary life in a simple nest above the ground, while most rabbits live in social groups underground in burrows or warrens. Hares are generally larger than rabbits, with ears that are more elongated, and with hind legs that are larger and longer. Hares have not been domesticated, while descendants of the European rabbit are commonly bred as livestock and kept as pets

Rabbits have long been domesticated. Beginning in the Middle Ages, the European rabbit has been widely kept as livestock, starting in ancient RomeSelective breeding has generated a wide variety of rabbit breeds, many of which (since the early 19th century) are also kept as pets. Some strains of rabbit have been bred specifically as research subjects.

As livestock, rabbits are bred for their meat and fur. The earliest breeds were important sources of meat, and so became larger than wild rabbits, but domestic rabbits in modern times range in size from dwarf to giant. Rabbit fur, prized for its softness, can be found in a broad range of coat colors and patterns, as well as lengths. The Angora rabbit breed, for example, was developed for its long, silky fur, which is often hand-spun into yarn. Other domestic rabbit breeds have been developed primarily for the commercial fur trade, including the Rex, which has a short plush coat.

Because the rabbit’s epiglottis is engaged over the soft palate except when swallowing, the rabbit is an obligate nasal breather. Rabbits have two sets of incisor teeth, one behind the other. This way they can be distinguished from rodents, with which they are often confused.[6] Carl Linnaeus originally grouped rabbits and rodents under the class Glires; later, they were separated as the scientific consensus is that many of their similarities were a result of convergent evolution. However, recent DNA analysis and the discovery of a common ancestor has supported the view that they do share a common lineage, and thus rabbits and rodents are now often referred to together as members of the superorder Glires.

Since speed and agility are a rabbit’s main defenses against predators (including the swift fox), rabbits have large hind leg bones and well developed musculature. Though plantigrade at rest, rabbits are on their toes while running, assuming a more digitigrade form. Rabbits use their strong claws for digging and (along with their teeth) for defense.[8] Each front foot has four toes plus a dewclaw. Each hind foot has four toes (but no dewclaw).[9]

Most wild rabbits (especially compared to hares) have relatively full, egg-shaped bodies. The soft coat of the wild rabbit is agouti in coloration (or, rarely, melanistic), which aids in camouflage. The tail of the rabbit (with the exception of the cottontail species) is dark on top and white below. Cottontails have white on the top of their tails.

Rabbits have muscled hind legs that allow for maximum force, maneuverability, and acceleration that is divided into three main parts; foot, thigh, and leg. The hind limbs of a rabbit are an exaggerated feature, that are much longer than the forelimbs providing more force. Rabbits run on their toes to gain the optimal stride during locomotion. The force put out by the hind limbs is contributed to both the structural anatomy of the fusion tibia and fibula, and muscular features.[16] Bone formation and removal, from a cellular standpoint, is directly correlated to hind limb muscles. Action pressure from muscles creates force that is then distributed through the skeletal structures. Rabbits that generate less force, putting less stress on bones are more prone to osteoporosis due to bone rarefaction.[17] In rabbits, the more fibers in a muscle, the more resistant to fatigue. For example, hares have a greater resistant to fatigue than cottontails. The muscles of rabbit’s hind limbs can be classified into four main categories: hamstringsquadricepsdorsiflexors, or plantar flexors. The quadricep muscles are in charge of force production when jumping. Complimenting these muscles are the hamstrings which aid in short bursts of action. These muscles play off of one another in the same way as the plantar flexors and doriflexors, contributing to the generation and actions associated with force.

Within the order lagomorphs, the ears are utilized to detect and avoid predators. In the family leporidae, the ears are typically longer than they are wide. For example, in black tailed jack rabbits, their long ears cover a greater surface area relative to their body size that allow them to detect predators from far away. Contrasted to cotton tailed rabbits, their ears are smaller and shorter, requiring predators to be closer to detect them before fleeing. Evolution has favored rabbits to have shorter ears so the larger surface area does not cause them to lose heat in more temperate regions. The opposite can be seen in rabbits that live in hotter climates, mainly because they possess longer ears that have a larger surface area that help with dispersion of heat as well as the theory that sound does not travel well in more arid air, opposed to cooler air. Therefore, longer ears are meant to aid the organism in detecting prey sooner rather than later in warmer temperatures.[19] The rabbit is characterized by its shorter ears while hares are characterized by their longer ears.[20] Rabbits ears are an important structure to aid thermoregulation and detect predators due to how the outer, middle, and inner ear muscles coordinate with one another. The ear muscles also aid in maintaining balance and movement when fleeing predators.

 

SALSA MUSIC

Salsa music is a popular dance music genre that initially arose in New York City during the 1960s. Salsa is the product of various musical genres including the Cuban son montunoguarachacha cha chámambo, and to a certain extent bolero, and the Puerto Rican bomba and plenaLatin jazz, which was also developed in New York City, has had a significant influence on salsa arrangers, piano guajeos, and instrumental soloists.[5]

Salsa is primarily Cuban son, itself a fusion of Spanish canción and guitar and Afro-Cuban percussion, merged with North American music styles such as jazz. Salsa also occasionally incorporates elements of rockR&B, and funk.[6] All of these non-Cuban elements are grafted onto the basic Cuban son montuno template when performed within the context of salsa.[7]

The first salsa bands were predominantly Cubans and Puerto Ricans who moved to New York since the 1920s.[8][9][10] The music eventually spread throughout Colombia and the rest of the Americas.[11] Ultimately, it became a global phenomenon. Some of the founding salsa artists were Johnny Pacheco (the creator of the Fania All-Stars), Celia CruzRay BarrettoRubén BladesWillie ColónLarry HarlowRoberto RoenaBobby ValentínEddie Palmieri, and Héctor Lavoe.

Salsa as a musical term

Salsa means ‘sauce‘ in the Spanish language, and carries connotations of the spiciness common in Latin and Caribbean cuisine.[13] In the 20th century, salsa acquired a musical meaning in both English and Spanish. In this sense salsa has been described as a word with “vivid associations”.[14] Cubans and Puerto Ricans in New York have used the term analogously to swing or soul music. In this usage salsa connotes a frenzied, “hot” and wild musical experience that draws upon or reflects elements of Latin culture, regardless of the style.[15][16]

Various music writers and historians have traced the use of salsa to different periods of the 20th century. Max Salazar traces the word back to the early 1930s, when Ignacio Piñeiro composed “Échale salsita”, a Cuban son protesting tasteless food.[17] While Salazar describes this song as the origin of salsa meaning “danceable Latin music”, Ed Morales describes the usage in the same song as a cry from Piñeiro to his band, telling them to increase the tempo to “put the dancers into high gear”.[18] Morales claims that later in the 1930s, vocalist Beny Moré would shout salsa during a performance “to acknowledge a musical moment’s heat, to express a kind of cultural nationalist sloganeering [and to celebrate the] ‘hotness’ or ‘spiciness’ of Latin American cultures”.[18] World music author Sue Steward claims salsa was originally used in music as a “cry of appreciation for a particularly piquant or flashy solo”.[14] She cites the first use in this manner to a Venezuelan radio DJ named Phidias Danilo Escalona;[14][19] In 1955 Cheo Marquetticreated a new band called Conjunto Los Salseros and recorded some new songs ( Sonero and Que no muera el son ).In 1955 José Curbelo recorded some others salsa songs (La familia, La la la and Sun sun sun ba bae). The contemporary meaning of salsa as a musical genre can be traced back to New York City Latin music promoter Izzy Sanabria:[20]

In 1973, I hosted the television show Salsa which was the first reference to this particular music as salsa. I was using [the term] salsa, but the music wasn’t defined by that. The music was still defined as Latin music. And that was a very, very broad category, because it even includes mariachi music. It includes everything. So salsa defined this particular type of music… It’s a name that everyone could pronounce.[21]

Sanabria’s Latin New York magazine was an English language publication. Consequently, his promoted events were covered in The New York Times, as well as Time and Newsweek magazines. They reported on this “new” phenomenon taking New York by storm—salsa.[22]

But promotion certainly wasn’t the only factor in the music’s success, as Sanabria makes clear: “Musicians were busy creating the music but played no role in promoting the name salsa.”[23] Johnny Pacheco, the creative director and producer of Fania Records, molded New York salsa into a tight, polished and commercially successful sound. The unprecedented appeal of New York salsa, particularly the “Fania sound”, led to its adoption across Latin America and elsewhere.

Globally, the term salsa has eclipsed the original names of the various Cuban musical genres it encompasses. Ironically, Cuban-based music was promoted more effectively worldwide in the 1970s and 1980s by the salsa industry, than by Cuba. For a brief time in the early 1990s a fair number of Cuban musicians embraced the term, calling their own music salsa Cubana.[24] The practice did not catch on however.

 1235 N LOOP 336 WEST @ I-45  CONROE TX 77301

Kangaroo

 

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The kangaroo is a marsupial from the family Macropodidae (macropods, meaning “large foot”). In common use the term is used to describe the largest species from this family, especially those of the genus Macropus: the red kangarooantilopine kangarooeastern grey kangaroo, and western grey kangaroo. Kangaroos are indigenous to Australia. The Australian government estimates that 34.3 million kangaroos lived within the commercial harvest areas of Australia in 2011, up from 25.1 million one year earlier.

As with the terms “wallaroo” and “wallaby“, “kangaroo” refers to a paraphyletic grouping of species. All three refer to members of the same taxonomic family, Macropodidae, and are distinguished according to size. The largest species in the family are called “kangaroos” and the smallest are generally called “wallabies”. The term “wallaroos” refers to species of an intermediate size. There is also the tree-kangaroo, another genus of macropod, which inhabits the tropical rainforests of New Guinea, far northeastern Queensland and some of the islands in the region. A general idea of the relative size of these informal terms could be:

  • wallabies: head and body length of 45–105 cm and tail length of 33–75 cm; The dwarf wallaby (the smallest member) is 46 cm long and weighs 1.6 kg;
  • tree-kangaroos: from Lumholtz’s tree-kangaroo body and head length of 48–65 cm, tail of 60–74 cm, weight of 7.2 kg (16 lb) for males and 5.9 kg (13 lb) for females; to the grizzled tree-kangaroo length of 75–90 cm (30 to 35 in) and weight of 8–15 kg (18–33 lb);
  • wallaroos: the black wallaroo, the smallest by far, with a tail length of 60–70 cm and weight of 19–22 kg for males and 13 kg for females;
  • kangaroos: a large male can be 2 m (6 ft 7 in) tall and weighs 90 kg (200 lb).

Kangaroos have large, powerful hind legs, large feet adapted for leaping, a long muscular tail for balance, and a small head. Like most marsupials, female kangaroos have a pouch called a marsupium in which joeys complete postnatal development.

The large kangaroos have adapted much better than the smaller macropods to land clearing for pastoral agriculture and habitat changes brought to the Australian landscape by humans. Many of the smaller species are rare and endangered, while kangaroos are relatively plentiful.

The kangaroo is a symbol of Australia and appears on the Australian coat of arms  and on some of its currency  and is used by some of Australia’s well known organisations, including Qantas  and the Royal Australian Air Force. The kangaroo is important to both Australian culture and the national image, and consequently there are numerous popular culture references.

Wild kangaroos are shot for meat, leather hides, and to protect grazing land.[8] Although controversial, kangaroo meat has perceived health benefits for human consumption compared with traditional meats due to the low level of fat on kangaroos.

 

The word “kangaroo” derives from the Guugu Yimithirr word gangurru, referring to grey kangaroos. The name was first recorded as “kanguru” on 12 July 1770 in an entry in the diary of Sir Joseph Banks; this occurred at the site of modern Cooktown, on the banks of the Endeavour River, where HMS Endeavour under the command of Lieutenant James Cook was beached for almost seven weeks to repair damage sustained on the Great Barrier Reef. Cook first referred to kangaroos in his diary entry of 4 August. Guugu Yimithirr is the language of the people of the area.

A common myth about the kangaroo’s English name is that “kangaroo” was a Guugu Yimithirr phrase for “I don’t understand you.” According to this legend, Cook and Banks were exploring the area when they happened upon the animal. They asked a nearby local what the creatures were called. The local responded “Kangaroo”, meaning “I don’t understand you”, which Cook took to be the name of the creature. This myth was debunked in the 1970s by linguist John B. Haviland in his research with the Guugu Yimithirr people.

Kangaroos are often colloquially referred to as “roos”. Male kangaroos are called bucks, boomers, jacks, or old men; females are does, flyers, or jills; and the young ones are joeys. The collective noun for kangaroos is a mob, troop, or court.

There are four species that are commonly referred to as kangaroos:

  • The red kangaroo (Macropus rufus) is the largest surviving marsupial anywhere in the world. It occupies the arid and semi-arid centre of the country. The highest population densities of the red kangaroo occur in the rangelands of western New South Wales. Red kangaroos are commonly mistaken as the most abundant species of kangaroo, but eastern greys actually have a larger population. A large male can be 2 metres (6 ft 7 in) tall and weighs 90 kg (200 lb).
  • The eastern grey kangaroo (Macropus giganteus) is less well-known than the red (outside Australia), but the most often seen, as its range covers the fertile eastern part of the country. The range of the eastern grey kangaroo extends from the top of the Cape York Peninsula in north Queensland down to Victoria, as well as areas of south-eastern Australia and Tasmania. Population densities of eastern grey kangaroos usually peak near 100 per km2 in suitable habitats of open woodlands. Populations are more limited in areas of land clearance, such as farmland, where forest and woodland habitats are limited in size or abundance.
  • The western grey kangaroo (Macropus fuliginosus) is slightly smaller again at about 54 kg (119 lb) for a large male. It is found in the southern part of Western Australia, South Australia near the coast, and the Darling River basin. The highest population densities occur in the western Riverina district of New South Wales and in western areas of the Nullarbor Plain in Western Australia. Populations may have declined, particularly in agricultural areas. The species has a high tolerance to the plant toxin sodium fluoroacetate, which indicates a possible origin from the south-west region of Australia.
  • The antilopine kangaroo (Macropus antilopinus) is, essentially, the far-northern equivalent of the eastern and western grey kangaroos. It is sometimes referred to as the antilopine wallaroo, but in behaviour and habitat it is more similar to red and grey kangaroos. Like them, it is a creature of the grassy plains and woodlands, and gregarious. Its name comes from its fur, which is similar in colour and texture to that of antelopes. Characteristically, the noses of males swell behind the nostrils. This enlarges nasal passages and allows them to release more heat in hot and humid climates.

Palatal view of a Sthenurus sp skull

In addition, there are about 50 smaller macropods closely related to the kangaroo in the family Macropodidae. Kangaroos and other macropods share a common ancestor with Phalangeridae from the mid-Miocene. This ancestor was likely arboreal and lived in the canopies of the extensive forests that covered most of Australia at that time, when the climate was much wetter, and fed on leaves and stems. From the late Miocene though the Pliocene and into the Pleistocene the climate got drier which led to a decline of forests and expansion of grasslands. At this time there was a radiation of macropodids characterised by enlarged body size and adaptation to the low quality grass diet with the development of foregut fermentation. The most numerous early macropods, the Balbaridae and Bulungmayinae, became extinct in the late Miocene around 5–10 mya. There is dispute over the relationships of the two groups to modern kangaroos and rat kangaroos. Some argue that the balbarines were the ancestors of rat kangaroos and the bulungmayines were the ancestors of kangaroos. while others hold the contrary view.

The Kongouro from New Holland, 1772 painting of a kangaroo by George Stubbs

The middle to late bulungmayines, Gungaroo and Wanburoo lacked digit 1 of the hind foot and digits 2 and 3 were reduced and partly under the large digit 4, much like the modern kangaroo foot. This would indicate that they were bipedal. In addition their ankle bones had an articulation that would have prohibited much lateral movements, an adaptation for bipedal hopping.  Species related to the modern grey kangaroos and wallaroos begin to appear in the Pliocene. The red kangaroo appears to be the most recently evolved kangaroo with its fossil record not going back beyond the Pleistocene period, 1–2 mya.

Europeans have long regarded kangaroos as strange animals. Early explorers described them as creatures that had heads like deer (without antlers), stood upright like men, and hopped like frogs. Combined with the two-headed appearance of a mother kangaroo, this led many back home to dismiss them as travellers’ tales for quite some time.[citation needed] The first kangaroo to be exhibited in the western world was an example shot by John Gore, an officer on Captain Cook’s Endeavour in 1770. The animal was shot and its skin and skull transported back to England whereupon it was stuffed (by taxidermists who had never seen the animal before) and displayed to the general public as a curiosity. The first glimpse of a kangaroo for many 18th-century Britons was a painting by George Stubbs.

Comparison with wallabies

Kangaroos and wallabies belong to the same taxonomic family (Macropodidae) and often the same genera, but kangaroos are specifically categorised into the six largest species of the family. The term wallaby is an informal designation generally used for any macropod that is smaller than a kangaroo or wallaroo that has not been designated otherwise.

 

Spiders

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Spiders (order Araneae) are air-breathing arthropods that have eight legs and chelicerae with fangs able to inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms.[2] Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of November 2015, at least 45,700 spider species, and 113 families have been recorded by taxonomists.[1] However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.[3]

Anatomically, spiders differ from other arthropods in that the usual body segments are fused into two tagmata, the cephalothorax and abdomen, and joined by a small, cylindrical pedicel. Unlike insects, spiders do not have antennae. In all except the most primitive group, the Mesothelae, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.

Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of glands. Spider webs vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-web spiders. Spider-like arachnids with silk-producing spigots appeared in the Devonianperiod about 386 million years ago, but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years ago, and are very similar to the most primitive surviving suborder, the Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appeared in the Triassic period, before 200 million years ago.

The species Bagheera kiplingi was described as herbivorous in 2008,[4] but all other known species are predators, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. It is estimated that the world’s 25 million tons of spiders kill 400–800 million tons of prey per year.[5] Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lassoing it with sticky bolas, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the genus Portia show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders’ guts are too narrow to take solids, so they liquefy their food by flooding it with digestive enzymes. They also grind food with the bases of their pedipalps, as arachnids do not have the mandibles that crustaceans and insects have.

To avoid being eaten by the females, which are typically much larger, male spiders identify themselves to potential mates by a variety of complex courtship rituals. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the widow spiders, to co-operative hunting and food-sharing. Although most spiders live for at most two years, tarantulas and other mygalomorph spiders can live up to 25 years in captivity.

While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticides. Spider silk provides a combination of lightness, strength and elasticity that is superior to that of synthetic materials, and spider silk genes have been inserted into mammals and plants to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and mythology symbolizing various combinations of patience, cruelty and creative powers. An abnormal fear of spiders is called arachnophobia.

Spiders are chelicerates and therefore arthropods.[6] As arthropods they have: segmented bodies with jointed limbs, all covered in a cuticle made of chitin and proteins; heads that are composed of several segments that fuse during the development of the embryo.[7] Being chelicerates, their bodies consist of two tagmata, sets of segments that serve similar functions: the foremost one, called the cephalothorax or prosoma, is a complete fusion of the segments that in an insect would form two separate tagmata, the head and thorax; the rear tagma is called the abdomen or opisthosoma.[6] In spiders, the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel.[8] The pattern of segment fusion that forms chelicerates’ heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the antennae typical of most arthropods. In fact, chelicerates’ only appendages ahead of the mouth are a pair of chelicerae, and they lack anything that would function directly as “jaws”.[7][9] The first appendages behind the mouth are called pedipalps, and serve different functions within different groups of chelicerates.[6]

Spiders and scorpions are members of one chelicerate group, the arachnids.[9] Scorpions’ chelicerae have three sections and are used in feeding.[10] Spiders’ chelicerae have two sections and terminate in fangs that are generally venomous, and fold away behind the upper sections while not in use. The upper sections generally have thick “beards” that filter solid lumps out of their food, as spiders can take only liquid food.[8] Scorpions’ pedipalps generally form large claws for capturing prey,[10] while those of spiders are fairly small appendages whose bases also act as an extension of the mouth; in addition, those of male spiders have enlarged last sections used for spermtransfer.[8]

In spiders, the cephalothorax and abdomen are joined by a small, cylindrical pedicel, which enables the abdomen to move independently when producing silk. The upper surface of the cephalothorax is covered by a single, convex carapace, while the underside is covered by two rather flat plates. The abdomen is soft and egg-shaped. It shows no sign of segmentation, except that the primitive Mesothelae, whose living members are the Liphistiidae, have segmented plates on the upper surface

Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas round the reproductive and excretory systems. Its place is largely taken by a hemocoel, a cavity that runs most of the length of the body and through which blood flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end.[11] However, in spiders, it occupies only the upper part of the abdomen, and blood is discharged into the hemocoel by one artery that opens at the rear end of the abdomen and by branching arteries that pass through the pedicle and open into several parts of the cephalothorax. Hence spiders have open circulatory systems.[8] The blood of many spiders that have book lungs contains the respiratory pigment hemocyanin to make oxygen transport more efficient.[9]

Spiders have developed several different respiratory anatomies, based on book lungs, a tracheal system, or both. Mygalomorph and Mesothelae spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen. This is also the case for some basal araneomorph spiders, like the family Hypochilidae, but the remaining members of this group have just the anterior pair of book lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs.[8] The trachea system has most likely evolved in small ancestors to help resist desiccation.[9] The trachea were originally connected to the surroundings through a pair of openings called spiracles, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and moved backwards close to the spinnerets.[8] Spiders that have tracheae generally have higher metabolic rates and better water conservation.[12] Spiders are ectotherms, so environmental temperatures affect their activity.

Uniquely among chelicerates, the final sections of spiders’ chelicerae are fangs, and the great majority of spiders can use them to inject venom into prey from venom glands in the roots of the chelicerae.[8] The families Uloboridae and Holarchaeidae, and some Liphistiidae spiders, have lost their venom glands, and kill their prey with silk instead.[14] Like most arachnids, including scorpions,[9] Spiders have a narrow gut that can only cope with liquid food and two sets of filters to keep solids out.[8] They use one of two different systems of external digestion. Some pump digestive enzymes from the midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the pedipalps, while flooding it with enzymes; in these species, the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing.[8]

The stomach in the cephalothorax acts as a pump that sends the food deeper into the digestive system. The mid gut bears many digestive ceca, compartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax.[8]

Most spiders convert nitrogenous waste products into uric acid, which can be excreted as a dry material. Malphigian tubules (“little tubes”) extract these wastes from the blood in the hemocoel and dump them into the cloacal chamber, from which they are expelled through the anus.[8] Production of uric acid and its removal via Malphigian tubules are a water-conserving feature that has evolved independently in several arthropod lineages that can live far away from water,[15] for example the tubules of insects and arachnids develop from completely different parts of the embryo.[9] However, a few primitive spiders, the sub-order Mesothelae and infra-order Mygalomorphae, retain the ancestral arthropod nephridia (“little kidneys“),[8] which use large amounts of water to excrete nitrogenous waste products as ammonia.[15]

Central nervous system

The basic arthropod central nervous system consists of a pair of nerve cords running below the gut, with paired ganglia as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the esophagus is encircled by this conglomeration of ganglia.[16] Except for the primitive Mesothelae, of which the Liphistiidae are the sole surviving family, spiders have the much more centralized nervous system that is typical of arachnids: all the ganglia of all segments behind the esophagus are fused, so that the cephalothorax is largely filled with nervous tissue and there are no ganglia in the abdomen;[8][9][16] in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused.[12]

Despite the relatively small central nervous system, some spiders (like Portia) exhibit complex behaviour, including the ability to use a trial-and-error approach.[17][18]

Sense organs

Eyes

This jumping spider‘s main ocelli(center pair) are very acute. The outer pair are “secondary eyes” and there are other pairs of secondary eyes on the sides and top of its head.[19]

Spiders have primarily four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another.[8] The principal pair at the front are of the type called pigment-cup ocelli (“little eyes”), which in most arthropods are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However, in spiders these eyes are capable of forming images.[19][20] The other pairs, called secondary eyes, are thought to be derived from the compound eyes of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the principal eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidum, and wolf spiders can be spotted by torch light reflected from the tapeta. On the other hand, jumping spiders’ secondary eyes have no tapeta.[8]

Other differences between the principal and secondary eyes are that the latter have rhabdomeres that point away from incoming light, just like in vertebrates, while the arrangement is the opposite in the former. The principal eyes are also the only ones with eye muscles, allowing them to move the retina. Having no muscles, the secondary eyes are immobile.[21]

Some jumping spiders’ visual acuity exceeds by a factor of ten that of dragonflies, which have by far the best vision among insects; in fact the human eye is only about five times sharper than a jumping spider’s. They achieve this by a telephoto-like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.[17]

There are spiders with a reduced number of eyes, of these those with six-eyes are the most numerous and are missing a pair of eyes on the anterior median line,[22] others species have four-eyes and some just two. Cave dwelling species have no eyes, or possess vestigial eyes incapable of sight.

Other senses

As with other arthropods, spiders’ cuticles would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact, spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called setae, respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste and smell, often by means of setae.[19] An adult Araneus may have up to 1000 such chemosensitive setae, most on the tarsi of the first pair of legs. Males have more chemosensitive hairs on their pedipalps than females. They have been shown to be responsive to sex pheromones produced by females, both contact and air-borne.[23] Spiders also have in the joints of their limbs slit sensillae that detects force and vibrations. In web-building spiders, all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively.[8]

Like most arthropods, spiders lack balance and acceleration sensors and rely on their eyes to tell them which way is up. Arthropods’ proprioceptors, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. On the other hand, little is known about what other internal sensors spiders or other arthropods may have.[19]

Locomotion

Image of a spider leg: 1–coxa; 2–trochanter; 3–femur; 4–patella; 5–tibia; 6–metatarsus; 7–tarsus; 8–claws

Each of the eight legs of a spider consists of seven distinct parts. The part closest to and attaching the leg to the cephalothorax is the coxa; the next segment is the short trochanter that works as a hinge for the following long segment, the femur; next is the spider’s knee, the patella, which acts as the hinge for the tibia; the metatarsus is next, and it connects the tibia to the tarsus (which may be thought of as a foot of sorts); the tarsus ends in a claw made up of either two or three points, depending on the family to which the spider belongs. Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors.[24] The only extensor muscles in spider legs are located in the three hip joints (bordering the coxa and the trochanter).[25] As a result, a spider with a punctured cephalothorax cannot extend its legs, and the legs of dead spiders curl up.[8] Spiders can generate pressures up to eight times their resting level to extend their legs,[26] and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs.[8] Although larger spiders use hydraulics to straighten their legs, unlike smaller jumping spiders they depend on their flexormuscles to generate the propulsive force for their jumps.[25]

Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine hairs between the paired claws at the tips of their legs. These tufts, known as scopulae, consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces.[8] Spiders, like most other arachnids, keep at least four legs on the surface while walking or running.[27]

Silk production

An orb weaver producing silk from its spinnerets

The abdomen has no appendages except those that have been modified to form one to four (usually three) pairs of short, movable spinnerets, which emit silk. Each spinneret has many spigots, each of which is connected to one silk gland. There are at least six types of silk gland, each producing a different type of silk.[8]

Silk is mainly composed of a protein very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein.[28] It is similar in tensile strength to nylon and biological materials such as chitincollagen and cellulose, but is much more elastic. In other words, it can stretch much further before breaking or losing shape.[8]

Some spiders have a cribellum, a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum, a comb-like set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However, most modern groups of spiders have lost the cribellum.[8]

Tarantulas also have silk glands in their feet.[29]

Even species that do not build webs to catch prey use silk in several ways: as wrappers for sperm and for fertilized eggs; as a “safety rope“; for nest-building; and as “parachutes” by the young of some species.[8]

Reproduction and life cycle

File:Neriene radiata - 2013-07-04.webm

Mating behaviour of Neriene radiata

The tiny male of the Golden orb weaver (Nephila clavipes) (near the top of the leaf) is protected from the female by his producing the right vibrations in the web, and may be too small to be worth eating.

Spiders reproduce sexually and fertilization is internal but indirect, in other words the sperm is not inserted into the female’s body by the male’s genitals but by an intermediate stage. Unlike many land-living arthropods,[30] male spiders do not produce ready-made spermatophores (packages of sperm), but spin small sperm webs on to which they ejaculate and then transfer the sperm to special syringe-like structures, palpal bulbs or palpal organs, borne on the tips of the pedipalps of mature males. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or “safety ropes”, the male can identify the species and sex of these objects by “smell”.[8]

Spiders generally use elaborate courtship rituals to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In web-weaving species, precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female’s body are important in many spiders that hunt actively, and may “hypnotize” the female. Gestures and dances by the male are important for jumping spiders, which have excellent eyesight. If courtship is successful, the male injects his sperm from the palpal bulbs into the female’s genital opening, known as the epigyne, on the underside of her abdomen. Female’s reproductive tracts vary from simple tubes to systems that include seminal receptacles in which females store sperm and release it when they are ready.[8] Because the sperm is stored in the epigyne, the eggs are not fertilized while inside the female, but during oviposition when the stored sperm is released from its chamber. The only known exception is a spider from Israel, Harpactea sadistica, which has evolved traumatic insemination. In this species the male will penetrate its pedipalps through the female’s body wall and inject his sperm directly into her ovaries, where the embryos inside the fertilized eggs will start to develop before being laid.[31]

Males of the genus Tidarren amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of male’s body mass in this species, and detaching one of the two improves mobility. In the Yemeni species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female’s epigynum for about four hours and apparently continues to function independently. In the meantime, the female feeds on the palpless male.[32] In over 60% of cases, the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female’s genital opening; in fact, the males co-operate by trying to impale themselves on the females’ fangs. Observation shows that most male redbacks never get an opportunity to mate, and the “lucky” ones increase the likely number of offspring by ensuring that the females are well-fed.[33] However, males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates’ webs.

Females lay up to 3,000 eggs in one or more silk egg sacs,[8] which maintain a fairly constant humidity level.[34] In some species, the females die afterwards, but females of other species protect the sacs by attaching them to their webs, hiding them in nests, carrying them in the chelicerae or attaching them to the spinnerets and dragging them along.[8]

Baby spiders pass all their larval stages inside the egg and hatch as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a wolf spider‘s brood cling to rough bristles on the mother’s back,[8] and females of some species respond to the “begging” behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitate food.[34]

Like other arthropods, spiders have to molt to grow as their cuticle (“skin”) cannot stretch.[35] In some species males mate with newly molted females, which are too weak to be dangerous to the males.[34] Most spiders live for only one to two years, although some tarantulas can live in captivity for over 20 years,[8][36] and an Australian female trapdoor spider was documented to have lived in the wild for 43 years, dying of a parasitic wasp attack.[37]

Size

Goliath birdeater (Theraphosa blondi), the largest spider

Spiders occur in a large range of sizes. The smallest, Patu digua from Colombia, are less than 0.37 mm (0.015 in) in body length. The largest and heaviest spiders occur among tarantulas, which can have body lengths up to 90 mm (3.5 in) and leg spans up to 250 mm (9.8 in).[38]

Coloration

Only three classes of pigment (ommochromesbilins and guanine) have been identified in spiders, although other pigments have been detected but not yet characterized. Melaninscarotenoids and pterins, very common in other animals, are apparently absent. In some species, the exocuticle of the legs and prosoma is modified by a tanning process, resulting in brown coloration.[39] Bilins are found, for example, in Micrommata virescens, resulting in its green color. Guanine is responsible for the white markings of the European garden spider Araneus diadematus. It is in many species accumulated in specialized cells called guanocytes. In genera such as TetragnathaLeucaugeArgyrodes or Theridiosoma, guanine creates their silvery appearance. While guanine is originally an end-product of protein metabolism, its excretion can be blocked in spiders, leading to an increase in its storage.[39] Structural colors occur in some species, which are the result of the diffraction, scattering or interference of light, for example by modified setae or scales. The white prosoma of Argiope results from hairs reflecting the light, Lycosa and Josaboth have areas of modified cuticle that act as light reflectors.[39]

Ecology and behavior

Non-predatory feeding

jumping spider seen in Chennai.

Although spiders are generally regarded as predatory, the jumping spider Bagheera kiplingi gets over 90% of its food from fairly solid plant material produced by acacias as part of a mutually beneficial relationship with a species of ant.[40]

Juveniles of some spiders in the families AnyphaenidaeCorinnidaeClubionidaeThomisidae and Salticidae feed on plant nectar. Laboratory studies show that they do so deliberately and over extended periods, and periodically clean themselves while feeding. These spiders also prefer sugar solutions to plain water, which indicates that they are seeking nutrients. Since many spiders are nocturnal, the extent of nectar consumption by spiders may have been underestimated. Nectar contains amino acidslipidsvitamins and minerals in addition to sugars, and studies have shown that other spider species live longer when nectar is available. Feeding on nectar avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes.[41]

Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on bananasmarmalademilkegg yolk and sausages.[41]

Capturing prey

The Phonognatha graeffei or leaf-curling spider’s web serves both as a trap and as a way of making its home in a leaf.

The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations.[8]

Females of the water spider Argyroneta aquatica build underwater “diving bell” webs that they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it.[42] A few spiders use the surfaces of lakes and ponds as “webs”, detecting trapped insects by the vibrations that these cause while struggling.[8]

Net-casting spiders weave only small webs, but then manipulate them to trap prey. Those of the genus Hyptiotes and the family Theridiosomatidae stretch their webs and then release them when prey strike them, but do not actively move their webs. Those of the family Deinopidae weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs’ area by a factor of up to ten. Experiments have shown that Deinopis spinosus has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of Deinopis subrufa appears to live mainly on tipulid flies that they catch with the backwards strike.[43]

Mature female bolas spiders of the genus Mastophora build “webs” that consist of only a single “trapeze line”, which they patrol. They also construct a bolas made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromones of moths, and then swing the bolas at the moths. Although they miss on about 50% of strikes, they catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas.[44][45] Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract moth flies, and catch them with their front pairs of legs.[46]

A trapdoor spider in the genus Cyclocosmia, an ambush predator

The primitive Liphistiidae, the “trapdoor spiders” of the family Ctenizidae and many tarantulas are ambush predators that lurk in burrows, often closed by trapdoors and often surrounded by networks of silk threads that alert these spiders to the presence of prey.[12] Other ambush predators do without such aids, including many crab spiders,[8] and a few species that prey on bees, which see ultraviolet, can adjust their ultraviolet reflectance to match the flowers in which they are lurking.[39] Wolf spidersjumping spidersfishing spiders and some crab spiders capture prey by chasing it, and rely mainly on vision to locate prey.[8]

Portia uses both webs and cunning, versatile tactics to overcome prey.[47]

Some jumping spiders of the genus Portia hunt other spiders in ways that seem intelligent,[17] outflanking their victims or luring them from their webs. Laboratory studies show that Portias instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species.[47] However, they seem to be relatively slow “thinkers”, which is not surprising, as their brains are vastly smaller than those of mammalian predators.[17]

Ant-mimicking spiders face several challenges: they generally develop slimmer abdomens and false “waists” in the cephalothorax to mimic the three distinct regions (tagmata) of an ant’s body; they wave the first pair of legs in front of their heads to mimic antennae, which spiders lack, and to conceal the fact that they have eight legs rather than six; they develop large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective hairs to resemble the shiny bodies of ants. In some spider species, males and females mimic different ant species, as female spiders are usually much larger than males. Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant; for example, many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus Synemosyna walk on the outer edges of leaves in the same way as Pseudomyrmex. Ant-mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However, several ant-mimicking spiders prey either on ants or on the ants’ “livestock“, such as aphids. When at rest, the ant-mimicking crab spider Amyciaea does not closely resemble Oecophylla, but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill, some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.[48]

Defense

Threat display by a Sydney funnel-web spider (Atrax robustus).

There is strong evidence that spiders’ coloration is camouflage that helps them to evade their major predators, birds and parasitic wasps, both of which have good color vision. Many spider species are colored so as to merge with their most common backgrounds, and some have disruptive coloration, stripes and blotches that break up their outlines. In a few species, such as the Hawaiian happy-face spider, Theridion grallator, several coloration schemes are present in a ratio that appears to remain constant, and this may make it more difficult for predators to recognize the species. Most spiders are insufficiently dangerous or unpleasant-tasting for warning coloration to offer much benefit. However, a few species with powerful venoms, large jaws or irritant hairs have patches of warning colors, and some actively display these colors when threatened.[39][49]

Many of the family Theraphosidae, which includes tarantulas and baboon spiders, have urticating hairs on their abdomens and use their legs to flick them at attackers. These hairs are fine setae (bristles) with fragile bases and a row of barbs on the tip. The barbs cause intense irritation but there is no evidence that they carry any kind of venom.[50] A few defend themselves against wasps by including networks of very robust threads in their webs, giving the spider time to flee while the wasps are struggling with the obstacles.[51] The golden wheeling spider, Carparachne aureoflava, of the Namibian desert escapes parasitic wasps by flipping onto its side and cartwheeling down sand dunes.[52]

Socialization

A few spider species that build webs live together in large colonies and show social behavior, although not as complex as in social insectsAnelosimus eximius (in the family Theridiidae) can form colonies of up to 50,000 individuals.[53] The genus Anelosimus has a strong tendency towards sociality: all known American species are social, and species in Madagascar are at least somewhat social.[54] Members of other species in the same family but several different genera have independently developed social behavior. For example, although Theridion nigroannulatum belongs to a genus with no other social species, T. nigroannulatum build colonies that may contain several thousand individuals that co-operate in prey capture and share food.[55]Other communal spiders include several Philoponella species (family Uloboridae), Agelena consociata (family Agelenidae) and Mallos gregalis (family Dictynidae).[56] Social predatory spiders need to defend their prey against kleptoparasites (“thieves”), and larger colonies are more successful in this.[57] The herbivorous spider Bagheera kiplingi lives in small colonies which help to protect eggs and spiderlings.[40] Even widow spiders (genus Latrodectus), which are notoriously cannibalistic, have formed small colonies in captivity, sharing webs and feeding together.[58]

Web types

The large orb web of Araneus diadematus (European garden spider).

There is no consistent relationship between the classification of spiders and the types of web they build: species in the same genus may build very similar or significantly different webs. Nor is there much correspondence between spiders’ classification and the chemical composition of their silks. Convergent evolution in web construction, in other words use of similar techniques by remotely related species, is rampant. Orb web designs and the spinning behaviors that produce them are the best understood. The basic radial-then-spiral sequence visible in orb webs and the sense of direction required to build them may have been inherited from the common ancestors of most spider groups.[59] However, the majority of spiders build non-orb webs. It used to be thought that the sticky orb web was an evolutionary innovation resulting in the diversification of the Orbiculariae. Now, however, it appears that non-orb spiders are a sub-group that evolved from orb-web spiders, and non-orb spiders have over 40% more species and are four times as abundant as orb-web spiders. Their greater success may be because sphecid wasps, which are often the dominant predators of spiders, much prefer to attack spiders that have flat webs.[60]

Orb

Nephila clavata, a golden orb weaver

About half the potential prey that hit orb webs escape. A web has to perform three functions: intercepting the prey (intersection), absorbing its momentum without breaking (stopping), and trapping the prey by entangling it or sticking to it (retention). No single design is best for all prey. For example: wider spacing of lines will increase the web’s area and hence its ability to intercept prey, but reduce its stopping power and retention; closer spacing, larger sticky droplets and thicker lines would improve retention, but would make it easier for potential prey to see and avoid the web, at least during the day. However, there are no consistent differences between orb webs built for use during the day and those built for use at night. In fact, there is no simple relationship between orb web design features and the prey they capture, as each orb-weaving species takes a wide range of prey.[59]

The hubs of orb webs, where the spiders lurk, are usually above the center, as the spiders can move downwards faster than upwards. If there is an obvious direction in which the spider can retreat to avoid its own predators, the hub is usually offset towards that direction.[59]

Horizontal orb webs are fairly common, despite being less effective at intercepting and retaining prey and more vulnerable to damage by rain and falling debris. Various researchers have suggested that horizontal webs offer compensating advantages, such as reduced vulnerability to wind damage; reduced visibility to prey flying upwards, because of the back-lighting from the sky; enabling oscillations to catch insects in slow horizontal flight. However, there is no single explanation for the common use of horizontal orb webs.[59]

Spiders often attach highly visible silk bands, called decorations or stabilimenta, to their webs. Field research suggests that webs with more decorative bands captured more prey per hour.[61] However, a laboratory study showed that spiders reduce the building of these decorations if they sense the presence of predators.[62]

There are several unusual variants of orb web, many of them convergently evolved, including: attachment of lines to the surface of water, possibly to trap insects in or on the surface; webs with twigs through their centers, possibly to hide the spiders from predators; “ladder-like” webs that appear most effective in catching moths. However, the significance of many variations is unclear.[59]

In 1973, Skylab 3 took two orb-web spiders into space to test their web-spinning capabilities in zero gravity. At first, both produced rather sloppy webs, but they adapted quickly.[63]

Cobweb

A funnel web.

Members of the family Theridiidae weave irregular, tangled, three-dimensional webs, popularly known as cobwebs. There seems to be an evolutionary trend towards a reduction in the amount of sticky silk used, leading to its total absence in some species. The construction of cobwebs is less stereotyped than that of orb-webs, and may take several days.[60]

Other

The Linyphiidae generally make horizontal but uneven sheets, with tangles of stopping threads above. Insects that hit the stopping threads fall onto the sheet or are shaken onto it by the spider, and are held by sticky threads on the sheet until the spider can attack from below.[64]

Fossil record

Spider preserved in amber

Although the fossil record of spiders is considered poor,[65] almost 1000 species have been described from fossils.[66] Because spiders’ bodies are quite soft, the vast majority of fossil spiders have been found preserved in amber.[66] The oldest known amber that contains fossil arthropods dates from 130 million years ago in the Early Cretaceous period. In addition to preserving spiders’ anatomy in very fine detail, pieces of amber show spiders mating, killing prey, producing silk and possibly caring for their young. In a few cases, amber has preserved spiders’ egg sacs and webs, occasionally with prey attached;[67] the oldest fossil web found so far is 100 million years old.[68] Earlier spider fossils come from a few lagerstätten, places where conditions were exceptionally suited to preserving fairly soft tissues.[67]

The oldest known exclusively terrestrial arachnid is the trigonotarbid Palaeotarbus jerami, from about 420 million years ago in the Silurian period, and had a triangular cephalothorax and segmented abdomen, as well as eight legs and a pair of pedipalps.[69] Attercopus fimbriunguis, from 386 million years ago in the Devonian period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider at the time of its discovery.[70] However, these spigots may have been mounted on the underside of the abdomen rather than on spinnerets, which are modified appendages and whose mobility is important in the building of webs. Hence Attercopus and the similar Permian arachnid Permarachne may not have been true spiders, and probably used silk for lining nests or producing egg-cases rather than for building webs.[71] The largest known fossil spider as of 2011 is the araneid Nephila jurassica, from about 165 million years ago, recorded from DaohuogoInner Mongolia in China.[72] Its body length is almost 25 mm, (i.e., almost one inch).

Several Carboniferous spiders were members of the Mesothelae, a primitive group now represented only by the Liphistiidae.[70] The mesothelid Paleothele montceauensis, from the Late Carboniferous over 299 million years ago, had five spinnerets.[73] Although the Permian period 299 to 251 million years ago saw rapid diversification of flying insects, there are very few fossil spiders from this period.[70]

The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appear in the Triassic well before 200 million years ago. Some Triassic mygalomorphs appear to be members of the family Hexathelidae, whose modern members include the notorious Sydney funnel-web spider, and their spinnerets appear adapted for building funnel-shaped webs to catch jumping insects. Araneomorphae account for the great majority of modern spiders, including those that weave the familiar orb-shaped webs. The Jurassic and Cretaceous periods provide a large number of fossil spiders, including representatives of many modern families.[70]

Family tree

Shultz (2007)’s evolutionary family tree of arachnids[74] –  marks extinct groups.

It is now agreed that spiders (Araneae) are monophyletic (i.e., members of a group of organisms that form a clade, consisting of a last common ancestor and all of its descendants).[75] There has been debate about what their closest evolutionary relatives are, and how all of these evolved from the ancestral chelicerates, which were marine animals. The cladogram on the right is based on J. W. Shultz’ analysis (2007). Other views include proposals that: scorpions are more closely related to the extinct marine scorpion-like eurypterids than to spiders; spiders and Amblypygi are a monophyletic group. The appearance of several multi-way branchings in the tree on the right shows that there are still uncertainties about relationships between the groups involved.[75]

Arachnids lack some features of other chelicerates, including backward-pointing mouths and gnathobases (“jaw bases”) at the bases of their legs;[75] both of these features are part of the ancestral arthropod feeding system.[76] Instead, they have mouths that point forwards and downwards, and all have some means of breathing air.[75] Spiders (Araneae) are distinguished from other arachnid groups by several characteristics, including spinnerets and, in males, pedipalps that are specially adapted for sperm transfer.

Spiders are divided into two suborders, Mesothelae and Opisthothelae, of which the latter contains two infraorders, Mygalomorphae and Araneomorphae. Nearly 46,000 living species of spiders (order Araneae) have been identified and as of 2009 grouped into about 117 families and about 4,100 genera by arachnologists.[1]

Spider diversity[1][77]
(numbers are approximate)
Features
Suborder/Infraorder Families Genera Species Segmented plates on top of abdomen[78] Ganglia in abdomen Spinnerets[78] Striking direction of fangs[8]
Mesothelae 1 8 116 Yes Yes Four pairs, in some species one pair fused, under middle of abdomen Downwards and forwards
OpisthothelaeMygalomorphae 20 350 2,900 Only in some fossils No One, two or three pairs under rear of abdomen
Opisthothelae: Araneomorphae 96 3,700 44,000 From sides to center, like pincers

Mesothelae

The only living members of the primitive Mesothelae are the family Liphistiidae, found only in Southeast AsiaChina, and Japan.[77] Most of the Liphistiidae construct silk-lined burrows with thin trapdoors, although some species of the genus Liphistius build camouflaged silk tubes with a second trapdoor as an emergency exit. Members of the genus Liphistius run silk “tripwires” outwards from their tunnels to help them detect approaching prey, while those of genus Heptathela do not and instead rely on their built-in vibration sensors.[80] Spiders of the genus Heptathela have no venom glands although they do have venom gland outlets on the fang tip.[81]

The extinct families Arthrolycosidae, found in Carboniferous and Permian rocks, and Arthromygalidae, so far found only in Carboniferous rocks, have been classified as members of the Mesothelae.[82]

Mygalomorphae

A Mexican red-kneed tarantula Brachypelma smithi

The Mygalomorphae, which first appeared in the Triassic period,[70] are generally heavily built and hairy, with large, robust chelicerae and fangs.[77] Well-known examples include tarantulasctenizid trapdoor spiders and the Australasian funnel-web spiders.[8] Most spend the majority of their time in burrows, and some run silk tripwires out from these, but a few build webs to capture prey. However, mygalomorphs cannot produce the pirifom silk that the Araneomorphae use as instant adhesive to glue silk to surfaces or to other strands of silk, and this makes web construction more difficult for mygalomorphs. Since mygalomorphs rarely “balloon” by using air currents for transport, their populations often form clumps.[77] In addition to arthropods, mygalomorphs are capable of preying on frogs, small mammals, lizards, and snails.[83]

Araneomorphae

In addition to accounting for over 90% of spider species, the Araneomorphae, also known as the “true spiders”, include orb-web spiders, the cursorial wolf spiders, and jumping spiders,[77] as well as the only known herbivorous spider, Bagheera kiplingi.[40] They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae, which have fangs that are nearly parallel in alignment.[84]

Human interaction

Bites

All symptoms associated with toxic spider bites[85]

Although spiders are widely feared, only a few species are dangerous to people.[86] Spiders will only bite humans in self-defense, and few produce worse effects than a mosquito bite or bee-sting.[87] Most of those with medically serious bites, such as recluse spiders (genus Loxosceles) and widow spiders (genus Latrodectus), would rather flee and bite only when trapped, although this can easily arise by accident.[88][89] The defensive tactics of Australian funnel-web spiders (family Atracidae) include fang display. Their venom, although they rarely inject much, has resulted in 13 attributed human deaths over 50 years.[90] They have been deemed to be the world’s most dangerous spiders on clinical and venom toxicity grounds,[86] though this claim has also been attributed to the Brazilian wandering spider (genus Phoneutria).[91]

There were about 100 reliably reported deaths from spider bites in the 20th century,[92] compared to about 1,500 from jellyfish stings.[93] Many alleged cases of spider bites may represent incorrect diagnoses,[94] which would make it more difficult to check the effectiveness of treatments for genuine bites.[95] A review published in 2016 agreed with this conclusion, showing that 78% of 134 published medical case studies of supposed spider bites did not meet the necessary criteria for a spider bite to be verified. In the case of the two genera with the highest reported number of bites, Loxosceles and Latrodectus, spider bites were not verified in over 90% of the reports. Even when verification had occurred, details of the treatment and its effects were often lacking.[96]

Chemical benefits

Cooked tarantula spiders are considered a delicacy in Cambodia.

Spider venoms may be a less polluting alternative to conventional pesticides, as they are deadly to insects but the great majority are harmless to vertebrates. Australian funnel web spiders are a promising source, as most of the world’s insect pests have had no opportunity to develop any immunity to their venom, and funnel web spiders thrive in captivity and are easy to “milk”. It may be possible to target specific pests by engineering genes for the production of spider toxins into viruses that infect species such as cotton bollworms.[97]

The Ch’ol Maya use a beverage created from the tarantula species Brachypelma vagans for the treatment of a condition they term ‘tarantula wind’, the symptoms of which include chest pain, asthma and coughing.[98]

Possible medical uses for spider venoms are being investigated, for the treatment of cardiac arrhythmia,[99] Alzheimer’s disease,[100] strokes,[101] and erectile dysfunction.[102] The peptide GsMtx-4, found in the venom of Brachypelma vagans, is being researched to determine whether or not it could effectively be used for the treatment of cardiac arrhythmiamuscular dystrophy or glioma.[98] Because spider silk is both light and very strong, attemptsare being made to produce it in goats‘ milk and in the leaves of plants, by means of genetic engineering.[103][104]

Spiders can also be used as food. Cooked tarantula spiders are considered a delicacy in Cambodia,[105] and by the Piaroa Indians of southern Venezuela – provided the highly irritant hairs, the spiders’ main defense system, are removed first.[106]

Arachnophobia

Arachnophobia is a specific phobia—it is the abnormal fear of spiders or anything reminiscent of spiders, such as webs or spider-like shapes. It is one of the most common specific phobias,[107][108] and some statistics show that 50% of women and 10% of men show symptoms.[109] It may be an exaggerated form of an instinctive response that helped early humans to survive,[110] or a cultural phenomenon that is most common in predominantly European societies.[111]

Spiders in Culture

This Moche ceramic depicts a spider, and dates from around 300 CE.

Spiders have been the focus of stories and mythologies of various cultures for centuries.[112] Uttu, the ancient Sumerian goddess of weaving, was envisioned as a spider spinning her web.[113][114] According to her main myth, she resisted her father Enki‘s sexual advances by ensconcing herself in her web,[114] but let him in after he promised her fresh produce as a marriage gift,[114] thereby allowing him to intoxicate her with beer and rape her.[114] Enki’s wife Ninhursag heard Uttu’s screams and rescued her,[114] removing Enki’s semen from her vagina and planting it in the ground to produce eight previously-nonexistent plants.[114] In a story told by the Roman poet Ovid in his MetamorphosesArachne was a Lydian girl who challenged the goddess Athena to a weaving contest.[115][116] Arachne won, but Athena destroyed her tapestry out of jealousy,[116][117] causing Arachne to hang herself.[116][117] In an act of mercy, Athena brought Arachne back to life as the first spider.[116][117] Stories about the trickster-spider Anansi are prominent in the folk traditions of the Asante people of Ghana.[118]

In some cultures, spiders have symbolized patience due to their hunting technique of setting webs and waiting for prey, as well as mischief and malice due to their venomous bites.[119] The Italian tarantella is a dance to rid the young woman of the lustful effects of a spider bite. Web-spinning also caused the association of the spider with creation myths, as they seem to have the ability to produce their own worlds.[120] Dreamcatchers are depictions of spiderwebs. The Moche people of ancient Peru worshipped nature.[121] They placed emphasis on animals and often depicted spiders in their art.[122]

Thanksgiving Traditions

Thanksgiving Turkey

Each year Americans in the United States celebrate the Thanksgiving holiday on the fourth Thursday of November. Most families follow traditions begun on the first Thanksgiving, but many have their own traditions that they follow each year. Here are some of the common traditions associated with “Turkey.

Travel
One of the best things about Thanksgiving is spending time with family. Many people live far from family members and travel long distances by car, train, or plane to be with their loved ones. Thanksgiving is the busiest travel day of the year!

The Feast
Traditional foods are a large part of Thanksgiving celebrations. Many families include the entire family in the food preparation. Traditional foods include turkey, stuffing, gravy, sweet potatoes, cornbread, mashed potatoes, and cranberry sauce. Many people serve pie for dessert at the end of the meal. Popular pie flavors are pumpkin, pecan, sweet potato, and apple.

 

Vegetarian Foods
Some families choose to serve vegetarian Thanksgiving dinners instead of a stuffed turkey. Some people eat vegetarian turkey, which is made out of tofu. Others prefer to eat squash, salads, or other fruit and vegetable dishes.

 

The Wishbone
Some families include breaking the turkey’s wishbone as part of their celebration. The wishbone is found attached to the breast meat in the turkey’s chest. After the meat has been removed and the wishbone has had a chance to become dry and brittle, two people each take one end of the bone, make a wish, and pull. Whoever ends up with the larger part of the bone gets their wish!

WHAT’S YOUR FAVORITE THANKSGIVING FOOD?

The Turkey Pardon
Each year at Thanksgiving, the President of the United States receives a gift of a live turkey (along with an alternate in case something happens to the official turkey). At a White House ceremony, the president traditionally “pardons” the National Thanksgiving Turkey and the alternate turkeys, allowing them to live out the rest of their lives on a farm.

 

Helping Others
Many generous folks use Thanksgiving as an opportunity to help the less fortunate. Some people volunteer to serve food at homeless shelters on Thanksgiving Day and others donate to shelters or participate in canned food drives.

TV
Television also plays a part in Thanksgiving celebrations. Many families watch the New York City Macy’s Thanksgiving Day Parade. The parade includes marching bands, floats, songs and performances from Broadway musicals, and giant helium-filled balloons! People may also enjoy televised football games.

macys-parade

Photograph by Stephen Chernin, Getty Images

After the Meal
After the feast families often do additional activities. Some like to take walks after eating such a large meal. Some people take naps. Others sit down together to play board or card games together.

Fast Facts

  • A ripe cranberry will bounce.
  • All turkeys and chickens have wishbones.
  • Canadians celebrate their own Thanksgiving every October.
  • Abraham Lincoln declared a national day of Thanksgiving in 1863.
  • The first Macy’s Thanksgiving Day Parade was held in 1924.