Spider

Taxobox
name = Spiders

---

image_width = 250px
image_caption = an Orb-weaver spider, Family: "Araneidae"
regnum = Animalia
phylum = Arthropoda
subphylum = Chelicerata
classis = Arachnida
ordo = Araneae
ordo_authority = Clerck, 1757
diversity_link = Araneae families
diversity = 111 families, c.40,000 species
subdivision_ranks = Suborders
subdivision =
Mesothelae

Mygalomorphae

Araneomorphae
"See table of families"

Spiders are predatory invertebrate animals that have two body segments, eight legs, no chewing mouth parts and no wings. They are classified in the order Araneae, one of several orders within the larger class of arachnids, a group that also contains scorpions, whip scorpions, mites, ticks, and opiliones (harvestmen). The study of spiders is called arachnology.

All spiders produce silk, a thin, strong protein strand extruded by the spider from spinnerets most commonly found on the end of the abdomen. Many species use it to trap insects in webs, although there are also many species that hunt freely. Silk can be used to aid in climbing, form smooth walls for burrows, build egg sacs, wrap prey, and temporarily hold sperm, among other applications.

All spiders except those in the families Uloboridae and Holarchaeidae, and in the suborder Mesothelae (together about 350 species) can inject venom to protect themselves or to kill prey. Only about 200 species, however, have bites that can pose health problems to humans.cite journal |url=http://www.ajtmh.org/cgi/content/full/71/2/239 |author=Diaz, James H. |year=2004 |title=The global epidemiology, syndromic classification, management, and prevention of spider bites |journal=American Journal of Tropical Medicine and Hygiene |volume=71 |issue=2 |pages=239–250 |quotes=no |pmid=15306718 |doi=10.1126/science.153.3744.1647] Many larger species' bites may be quite painful, but will not produce lasting health concerns.

Spiders are found all over the world, from the tropics to the Arctic, living underwater in silken domes they supply with air, and on the tops of mountains. In 1973, Skylab 3 took two spiders into space to test their web-spinning capabilities in zero gravity. [cite web |author=Thomson, Peggy and Park, Edwards
title=Odd Tales from the Smithsonian |url=http://smithsonianeducation.org/students/secrets_of_the_Smithsonian/spiders_in_space.html |accessdate=2008-07-21]

Description

Body plan

(1) four pairs of legs
(2) cephalothorax
(3) opisthosomaSpiders are chelicerates and therefore arthropods.cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=554-555] 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.cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=518-522 ] 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. 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".cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=559-564] The first appendages behind the mouth are called pedipalps, and serve different functions within different groups of chelicerates.

Spiders and scorpions are members of one chelicerate group, the arachnids. While scorpions' chelicerae are generally a modest pair of claws that they use in feeding,cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=565-569] spiders' terminate in fangs that are are generally venomous, and fold away behind the upper sections while not in use, while the upper sections generally have thick "beards" that filter solid lumps out of their food, as spiders can take only liquid food;cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=571-584] On the other hand scorpions' pedipalps generally form large claws for capturing prey, while those of spiders are fairly small sensors whose bases also act as an extension of the mouth; in addition those of male spiders have enlarged last sections used for sperm transfer.

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.

Spiders, unlike insects, have only two body segments (tagmata) instead of three: a fused head and thorax (called a cephalothorax or prosoma) and an abdomen (called the opisthosoma). The exception to this rule are the assassin spiders, whose cephalothorax seems to be almost divided into two independent units.Fact|date=October 2008. The abdomen and cephalothorax are connected with a thin waist called the pedicle or the "pregenital somite", a trait that allows the spider to move the abdomen in all directions. The pedicle (waist) is actually the last segment (somite) of the cephalothorax and is lost in most other members of the Arachnida (in scorpions it is only detectable in the embryos).Fact|date=October 2008

Circulation and respiration

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,cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=527-528 ] 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. The blood of many spiders that have book lungs contains the respiratory pigment hemocyanin to make oxygen tranport more efficient.

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. The trachea system has most likely evolved in small ancestors to help resist desiccation. 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. Spiders that have tracheae generally have higher metabolic rates and better water conservation.

Among smaller araneomorph spiders we can find species who have evolved also the anterior pair of book lungs into trachea, or the remaining book lungs are simply reduced or missing, and in a very few the book lungs have developed deep channels, apparently signs of evolution into tracheae.fact|date=October 2008 Some very small spiders in moist and sheltered habitats have no breathing organs at all, and instead breathe directly through their body surface.fact|date=October 2008

Feeding, digestion and excretion

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. Like all arachnids including scorpions, spiders have a narrow gut that can only cope with liquid food and spiders have two sets of filters to keep solids out. 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.

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.

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. 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,cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=529-530 ] for example the tubules of insects and arachnids develop from completely different parts of the embryo. However a few primitive spiders, the sub-order Mesothelae and infra-order Mygalomorphae, retain the ancestral arthropod nephridia ("little kidneys"),, which use large amounts of water to excrete nitrogenous waste products as ammonia.

Many spiders will store prey temporarily. Web-building spiders that have made a shroud of silk to quiet their envenomed prey's death struggles will often leave them in these shrouds and then consume them later.Fact|date=October 2008

Spiders are capable of digesting their own silk, so some spiders may eat their used webs. When a spider drops down on a single strand of silk and then returns, it will generally rapidly consume the strand of silk on its way back up.Fact|date=July 2007

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.cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=531-532 ] 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 archnids: "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; in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused.

ense organs

Most spiders have four pairs of eyes - two pairs of on the front and top of the head, and two pairs of compound eyes, at the front corners and on the sides. The 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 the main eyes at the front of spiders' heads are pigment-cup ocelli that are capable of forming images. [cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=578-580] The other eyes are 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 main eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum, and wolf spiders can be spotted by torch light reflected from the tapeta. On the other hand jumping spiders' secondary eyes have no tapeta. 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 fives 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. As a result their vision is ten times more acute than that of dragonflies and one fifth as sharp as that of humans. The downside is that the scanning and integrating processes are relatively slow.cite journal
author=Harland, D.P., and Jackson, R.R. | date=2000
title=“Eight-legged cats” and how they see - a review of recent research on jumping spiders (Araneae: Salticidae)
journal=Cimbebasia | volume=16 | pages=231-240
url=http://www.cogs.susx.ac.uk/ccnr/Papers/Downloads/Harland_Cimb2000.pdf PDF | accessdate=2008-10-11 ]

As with other arthropods, spider's 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.cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=532-537] Spider also have in the joints of their limbs slit sensors that detect vibration. 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.

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.

Spiders usually have eight eyes in various arrangements, a fact that is used to aid in taxonomically classifying different species. Fact|date=October 2008 Most species of the Haplogynae have six eyes, although some have eight (Plectreuridae), four (eg., Tetrablemma) or even two (most Caponiidae) eyes. Fact|date=October 2008 Sometimes one pair of eyes is better developed than the rest, or even, in some cave species, there are no eyes at all. Fact|date=October 2008 The main pair of eyes in jumping spiders even see in color. Fact|date=October 2008
Net-casting spiders have enormous, compound lenses that give a wide field of view and gather available light very efficiently. Fact|date=October 2008

Locomotion

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. [cite book
author=Barnes, R.S.K., Calow, P., Olive, P., Golding, D., and Spicer, J.
title=The Invertebrates: A Synthesis | publisher=Blackwell Publishing | date=2001
isbn=0632047615 | chapter=Invertebrates with Legs: the Arthropods and Similar Groups | page=168
url=http://books.google.co.uk/books?id=TBMsbe9efPgC&pg=PA168&dq=arthropod+hydraulic&sig=ACfU3U2CPJ_K9DDSTNMoj97Mutbl8DFLgg
accessdate=2008-09-25] As a result a spider with a punctured cephalothorax cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level in order to extend their legs, [cite journal
author=Parry, D.A., and Brown, R.H.J.
title=The Hydraulic Mechanism of the Spider Leg
journal=Journal of Experimental Biology | volume=36 | pages=423-433 | date=1959
url=http://jeb.biologists.org/cgi/reprint/36/2/423.pdf | accessdate=2008-09-25 ] 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.

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 brstles 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. Spiders, like most other arachnids, keep at least four legs on the surface while walking or running.citation
author=Anderson, D.T. | chapter=The Chelicerata | pages=325-349
title=Invertebrate Zoology | date=2001 | edition=2 | editor=Anderson, D.T.
publisher=Oxford University Press | isbn=0195513681]

The peacock spider is a jumping spider with extensible flaps around its abdomen, with which it is able to glide when jumping, as well as use for mating display.fact|date=October 2008

ilk production

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.

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. It is similar in tensile strength to nylon and biological materials such as chitin, collagen and cellulose, but is much more elastic, in other words it can stretch much further before breaking or losing shape.

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 wooly 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.

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.

The suborder "Mesothelae" is unique in having only two types of silk glands — thought to be the ancestral condition.fact|date=October 2008 Later some groups evolved (called ecribellate) that use silk threads dotted with sticky droplets to capture prey ranging from small arthropods to sometimes even small bats and birds.fact|date=October 2008

anchor|ReproductionReproduction and life cycle

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,cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=537-539] 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 syringe-like structures on the tips of their pedipalps. 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".

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 pedipalps into the female's 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.

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.cite journal |quotes=no |author=Knoflach, B. & van Harten, A. |year=2001 |title="Tidarren argo" sp. nov (Araneae: Theridiidae) and its exceptional copulatory behaviour: emasculation, male palpal organ as a mating plug and sexual cannibalism |journal=Journal of Zoology | volume=254 |pages=449–459 |doi=10.1017/S0952836901000954] 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.cite journal |quotes=no |author=Andrade, Maydianne C.B. |title=Risky mate search and male self-sacrifice in redback spiders |journal=Behavioral Ecology |year=2003 |volume=14 |pages=531–538 |doi=10.1093/beheco/arg015] 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.cite book
title=Biology of Spiders | author=Foelix, R.F.
publisher=Oxford University Press US | date=1996 | isbn=0195095944 | chapter=Reproduction | pages=176-212
url=http://books.google.co.uk/books?id=XUgyqxNKhyAC&dq=%22Biology+of+Spiders%22+Foelix&pg=PP1&ots=Ch4j60g2pL&sig=42rE8UvdN74f4pcxzWLAniivNaY&hl=en&sa=X&oi=book_result&resnum=4&ct=result#PPA176,M1
accessdate=2008-10-08 ]

Females lay up to 3,000 eggs in one or more silk egg sacs, which maintain a fairly constant humidity level. 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.

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, and females of some species respond to the "begging" behavior of their young by giving them their prey, provided it is no longer struggling, or even regurgitate food.

Like other arthropods, spiders have to molt in order to grow as their cuticles ("skins") cannot stretch.cite book
author=Ruppert, E.E., Fox, R.S., and Barnes, R.D. | title=Invertebrate Zoology
publisher=Brooks / Cole | edition=7 | isbn=0030259827 | date=2004 | pages=523-524 ] In some species males mate with newly-molted females, which are too weak to be dangerous to the males. Most spiders live for only one to two years, although some tarantulas have lived in captivity for up to 25 years.

After sexual maturity is reached, the general rule is that spiders stop molting,Fact|date=July 2007 but the females of some non-araneomorph species will continue to molt the rest of their lives.

ize

Spiders occur in a large range of sizes. The smallest, dwarf spiders of the subfamily Erigoninae, are less than 1 mm (about .05 inches) in body length. The largest and heaviest spiders occur among tarantulas, which can have body lengths up to 90 mm (about 3.5 inches) and leg spans up to 250 mm (about 10 inches). ["Spiders and their Kin", Herbert W. Levi and Lorna R. Levi, Golden Press, p. 20 and p. 44]

Coloration

Only three classes of pigment (ommochromes, bilins and guanine) have been identified in spiders, although other pigments have been detected but not yet characterized. Melanins, carotenoids 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.Oxford, G.S. & Gillespie, R.G. (1998). Evolution and Ecology of Spider Coloration. "Annual Review of Entomology" 43:619-643. DOI|10.1146/annurev.ento.43.1.619] 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 "Tetragnatha", "Leucauge", "Argyrodes" 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. 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 "Josa" both have areas of modified cuticle that act as light reflectors.

Ecology and behavior

Non-predatory feeding

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.citation
author=Meehan, C,J. Olson, E.J. and Curry, R.L. | date=21 August 2008
title=Exploitation of the Pseudomyrmex–Acacia mutualism by a predominantly vegetarian jumping spider ("Bagheera kiplingi")
conference=93^rd ESA Annual Meeting
url=http://eco.confex.com/eco/2008/techprogram/P12401.HTM | accessdate=2008-10-10 ]

Juveniles of some spiders in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae 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 under-estimated. Nectar contains amino acids, lipids, vitamins 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.cite journal |author=Jackson, R.R. "et al." |year=2001 |title=Jumping spiders (Araneae: Salticidae) that feed on nectar |journal=J. Zool. Lond. |volume=255 |pages=25–29 |url=http://xnelson.googlepages.com/Jacksonetal2001.pdf |format=PDF |doi=10.1017/S095283690100108X]

Various species are known to 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 bananas, marmalade, milk, egg yolk and sausages. In one praying mantis species, juveniles also actively feed on pollen and adults that capture pollen-laden insects eat the pollen as well. [cite journal
author=Beckman, N. and Hurd, L.E.
title=Pollen Feeding and Fitness in Praying Mantids: The Vegetarian Side of a Tritrophic Predator
journal=Environmental Entomology | volume=32 | issue=4 | date=August 2003 | pages= 881–885
doi=10.1603/0046-225X(2003)032 [0881:PFAFIP] 2.0.CO;2 ]

Methods of capturing prey

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.

Females of the water spider "Argyroneta aquatica" build underwater "diving bell" webs which 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. Very unusually for spiders, males of this species are about 30% percent larger than females, possibly because their mobile hunting style requires greater strength to overcome the resistance of the water. [cite journal
author=Schütz, D., and Taborsky, M.
title=Adaptations to an aquatic life may be responsible for the reversed sexual size dimorphism in the water spider, "Argyroneta aquatica"
journal=Evolutionary Ecology Research | date=2003 | volume=5 | issue=1 | pages=105–117
url=http://www.zoology.unibe.ch/behav/pdf_files/Schuetz_EvolEcolRes03.pdf | accessdate=2008-10-11] A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling.

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 subrufus" appears to live mainly on tipulid flies that they catch with the backwards strike. [cite journal
author=Coddington, J., and Sobrevila, C.
title=Web manipulation and two stereotyped attack behaviors in the ogre-faced spider "Deinopis spinosus" Marx (Araneae, Deinopidae).
journal=Journal of Arachnology | date=1987 | volume=15 | pages=213-225
url=http://www.americanarachnology.org/JoA_free/JoA_v15_n2/JoA_v15_p213.pdf | accessdate=2008-10-11]

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. [cite journal
author=Eberhard, W.G. | title=Aggressive Chemical Mimicry by a Bolas Spider
journal=Science | date=December 1977 | volume=198| issue=4322| pages=1173-1175
doi=10.1126/science.198.4322.1173
url=http://striweb.si.edu/publications/PDFs/Eberhard_Agreessive%20chemical%20mimicry.Science.1977.pdf
accessdate=2008-10-10 ] [cite journal
author=Eberhard, W.G.
title=The Natural History and Behavior of the Bolas Spider, Mastophora dizzydeani sp. n. (Araneae)
journal=Psyche | volume=87 | pages=143-170 | date=1980 | url=http://psyche.entclub.org/87/87-143.html
accessdate=2008-10-10 ] 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. [cite journal
author=Yeargan, K.V., and Quate, L.W. | title=Adult male bolas spiders retain juvenile hunting tactics
journal=Oecologia | date=1997 | volume=112 | issue=4 | pages=572-576 | doi=10.1007/s004420050347 ]

The primitive Liphistiidae, the "trapdoor spiders" (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. Other ambush predators do without such aids, including many crab spiders, 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. Wolf spiders, jumping spiders, fishing spiders and some crab spiders capture prey by chasing it, and rely mainly on vision to locate prey.

Some jumping spiders of the genus Portia hunt in ways that seem intelligent. When stalking web-building spiders, some of which would be dangerous opponents, they lure them out by vibrating the webs to mimic the struggle of a trapped insect or the courtship signals of a male spider, or approach along an overhanging twig or rock and abseil down a silk thread to kill the prey. Laboratory studies show that "Portia" learns very quickly how to overcome web-building spiders that neither it nor its evolutionary ancestors would have met in the wild. While some of "Portia"’s tactics are clearly instinctive, experiments have shown that these are only starting points for a trial-and-error approach from which these spiders learn very quickly.cite book
author=Wilcox, S. and Jackson, R. | chapter=Jumping Spider Tricksters | pages=27-34
title=The Cognitive Animal: Empirical and Theoretical Perspectives on Animal Cognition
editor=Bekoff, M., Allen, C., and Burghardt, G.M. |publisher=MIT Press | date=2002 | isbn=0262523221] However they seem to be relatively slow "thinkers", which is not surprising as their brains are vastly smaller than those of mammalian predators. Once within biting range, "Portia"s use different combat tactics against different prey spiders. On the other hand they simply stalk and rush unarmed prey such as flies, [cite journal
author=Harland, D.P., and Jackson, R.R.
title=A knife in the back: use of prey-specific attack tactics by araneophagic jumping spiders (Araneae: Salticidae)
journal=Journal of Zoology | volume=269 | issue=3 | pages=285-290 | date=April 2006
doi=10.1111/j.1469-7998.2006.00112.x ] and also capture prey by means of sticky webs.

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 form to their heads to mimic antennae, which spiders lack, and to conceal the fact that they have but 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. [cite journal
author=Mclver, J.D. and Stonedahl, G. | title=Myrmecomorphy: Morphological and Behavioral Mimicry of Ants
journal=Annual Review of Entomology | volume=38 | pages=351-377 | date=January 1993
doi=10.1146/annurev.en.38.010193.002031 ]

While spiders are generalist predators, in actuality their different methods of prey capture often determine the type of prey taken.fact | date=October 2008 Thus web-building spiders rarely capture caterpillars, and crab spiders that ambush prey in flowers capture more bees, butterflies and some flies than other insects.fact | date=October 2008 Groups of families that tend to take certain types of prey because of their prey capture methods are often called "guilds".fact | date=October 2008 A few spiders are more specialized in their prey capture. "Dysdera" captures and eats sowbugs, pillbugs and beetles, while pirate spiders eat only other spiders.fact | date=October 2008 Bolas spiders in the family Araneidae use sex pheromone analogs to capture only the males of certain moth species.fact | date=October 2008 Despite their generally broad prey ranges, spiders are one of the most important links in the regulation of the populations of insects.fact | date=October 2008

Defense

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. [cite web
title=Different smiles, single species | publisher=University of California Museum of Paleontology
url=http://evolution.berkeley.edu/evolibrary/article/_0_0/happyface_03 | accessdate=2008-10-10 ]

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. [cite journal
author=Cooke, J.A.L., Roth, V.D., and Miller, F.H. | title=The urticating hairs of theraphosid spiders
journal=American Museum novitates | issue=2498 | publisher=American Museum of Natural History
url=http://digitallibrary.amnh.org/dspace/handle/2246/2705 | accessdate=2008-10-11 ] 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. [cite journal
author=Blackledge, T.A., and Wenzel, J.W.
title=Silk Mediated Defense by an Orb Web Spider against Predatory Mud-dauber Wasps
journal=Behaviour | volume=138 | issue=2 | date=2001 | pages=155-171 | doi=10.1163/15685390151074357 ] Many spiders will attempt to protect themselves by biting, especially if they are unable to flee.fact | date=October 2008} Some other species have specialized defense tactics. For example, the golden wheeling spider ("Carparachne aureoflava") of the desert of Namibia escapes parasitic wasps by flipping onto its side and cartwheeling down sand dunes. [cite journal
author=Armstrong, S. | title=Fog, wind and heat - life in the Namib desert | date=14 July 1990
journal=New Scientist
url=http://www.newscientist.com/article/mg12717253.800-fog-wind-and-heat--life-in-the-namib-desert-researchersworking-in-one-of-the-worlds-most-hostile-environments-are-discoveringhowscores-of-species-manage-to-survive-but-will-the-research-station-itselfsurvive-as-namibia-gains-its-independence-.html
accessdate=2008-10-11 ]

ocial spiders

A few species of spiders that build webs live together in large colonies and show social behavior, although not as complex as in social insects. "Anelosimus eximius" (in the family Theridiidae) can form colonies of up to 50,000 individuals. Other communal spiders include several "Philoponella" species (family Uloboridae), "Agelena consociata" (family Agelenidae) and "Mallos gregalis" (family Dictynidae). [cite journal
author=Matsumoto, T. | date=1998
title=Cooperative prey capture in the communal web spider, "Philoponella raffray" (Araneae, Uloboridae)
journal=Journal of Arachnology | volume=26 | pages=392–396
url=http://www.americanarachnology.org/JoA_free/JoA_v26_n3/JoA_v26_p392.pdf | accessdate=2008-10-11 ] Social predatory spiders need to defend their prey against kleptoparasites ("thieves"), and and larger colonies are more successful in this. [cite journal
author=Cangialosi, K.R. | title=Social spider defense against kleptoparasitism
journal=Behavioral Ecology and Sociobiology | volume=27 | issue=1 | date=July 1990 | doi=10.1007/BF00183313 ] The vegetarian spider "Bagheera kiplingi " lives in small colonies which help to protect eggs and spiderlings. Even widow spiders (genus "Latrodectus"), which are notoriously aggressive and cannibalistic, have formed small colonies in captivity, sharing webs and feeding together. [cite journal
author=Bertani, R., Fukushima, C.S., and Martins, R.
title=Sociable widow spiders? Evidence of subsociality in " Latrodectus"Walckenaer, 1805 (Araneae, Theridiidae)
journal=Journal of Ethology | volume=26 | issue=2 | date=May 2008 | doi=10.1007/s10164-007-0082-8 ]

Web types

Tangleweb spiders

Members of this group (family Theridiidae) are characterized by irregular, messy-looking, tangled, three-dimensional (non-sticky) webs, also popularly known as cobwebs, generally low and anchored to the ground or floor and wall. They are commonly found in or near buildings; some build webs in bushes. The spider generally hangs in the center of its web, upside-down. Prey is generally ground-dwelling insects such as ants or crickets, in addition to small flying insects. These include the infamous black widows, the minute happyface spider, and thousands of other species.

Orb web spiders

Spiders in several families (eg., Araneidae, Tetragnathidae, Nephilidae) spin the familiar spiral snare that most people think of as the typical spider web. On average, an orb-weaving spider takes 30 minutes to an hour to weave a web. They range in size from quite large (6+ cm) to very small (<1 cm), but all are quite harmless to humans, beyond the shock entailed from walking into a face-height web and having a large spider dangling from your nose. Many of the daytime hunters have a 'ferocious' appearance, with spines or large 'fangs', but they are almost invariably inoffensive, preferring to drop on a dragline to the ground when disturbed, rather than bite, which can nevertheless be quite painful.

Other types of webs

Some (the Linyphiidae) make various forms of bowl- or dome-shaped webs with or without a flat sheet or a tangled web above or below. Some make a flat platform extending from a funnel-shaped retreat, with generally a tangle of silk above the web. The common northern hemisphere 'funnel-web', 'house' or 'grass' spiders are only superficially similar to the notorious Sydney funnel-web spider, and are generally considered to be quite harmless. Some of the more primitive group Atypidae may make tubular webs up the base of trees, from inside which they bite insects that land on the webbing. These spiders look quite ferocious, but are not generally considered to be particularly dangerous to humans.

Evolution

Family tree

Trigonotarbids, spider-like arachnids, were among the oldest known land arthropods. Like spiders, they were terrestrial, respired through book lungs, and walked on eight legs with two additional legs adapted to use around their mouth. However, they were not true spiders, not even ancestral to them, but represented independent offshoots of the Arachnida.

True spiders (thin-waisted arachnids) evolved about 400 million years ago, and were among the first species to live on land. They are distinguished by abdominal segmentation and silk producing spinnerets. The Pedipalpi (including whip scorpions) are believed to constitute the sister group to the Araneae.cite journal | author=Coddington, J.A. & Levi, H.W. | year=1991
title=Systematics and Evolution of Spiders (Araneae) |journal=Annu. Rev. Ecol. Syst. | volume=22
pages=565–592 |doi=10.1146/annurev.es.22.110191.003025]

Most of the early segmented fossil spiders belonged to the Mesothelae, a group of primitive spiders with the spinnerets placed underneath the middle of the abdomen, rather than at the end as in modern spiders (Opisthothelae). They were probably ground dwelling predators of other primitive arthropods. Silk may have been used simply as a protective covering for the eggs, a lining for a retreat hole, and later perhaps for simple ground sheet web and trapdoor construction.

As plant and insect life diversified so also did the spider's use of silk. Spiders with spinnerets at the end of the abdomen (Mygalomorphae and Araneomorphae) appeared more than 250 million years ago, presumably promoting the development of more elaborate sheet and maze webs for prey capture both on ground and foliage, as well as the development of the safety dragline.

By the Jurassic, the sophisticated aerial webs of the orb weaving spiders had already developed to take advantage of the rapidly diversifying groups of insects. A spider web preserved in amber, thought to be 110 million years old, shows evidence of a perfect orb web.Fact|date=February 2007 It is believed that adhesive capture threads, as opposed to cribellate threads, evolved about 135 million years ago.Opell, B. D. (1997). The material cost and stickiness of capture threads and the evolution of orb-weaving spiders. "Biological Journal of the Linnean Society" 62:443–458. ]

The ability to weave orb webs is thought to have been "lost", and sometimes even re-evolved or evolved separately, in different breeds of spiders since its first appearance.

Family tree

clade
label1=Chelicerata
1=clade
1=Xiphosura (horseshoe crabs)
2=clade
1=Eurypterida†
2=Chasmataspidida†
label3=Arachnida
3=clade
1=clade
1=Scorpiones
2=Opiliones (harvestmen)
2=clade
1=Pseudoscorpiones
2=Solifugae (sun spiders)
3=Palpigradi (microwhip scorpions)
4=clade
1=Trigonotarbida†
2=clade
1=Araneae (spiders)
2=clade
1=Haptopoda†
2=clade
1=Amblypygi (whip spiders)
2=clade
1=Thelyphonida (whip scorpions)
2=Schizomida
5=clade
1=Ricinulei (hooded tickspiders)
2=Anactinotrichida
3=Acariformes (mites)

An evolutionary family tree of arachnids [cite journal
author=Schultz, J.W.
title=A phylogenetic analysis of the arachnid orders based on morphological characters
journal=Zoological Journal of the Linnean Society | date=2007 | volume=150 | pages=221–265
doi=10.1111/j.1096-3642.2007.00284.x ] – † marks extinct groups.

It is now agreed that spiders (Araneae) are monophyletic, in other words members of a group that contains a common ancestor plus all and only its descendants.cite journal
author=Schultz, J.W.
title=A phylogenetic analysis of the arachnid orders based on morphological characters
journal=Zoological Journal of the Linnean Society | date=2007 | volume=150 | pages=221–265
doi=10.1111/j.1096-3642.2007.00284.x ] There has been debate about what are their closest evolutionary relatives 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 monopyhletic 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.

Taxonomy

clade
label1 = "Araneae"
1=clade
1 ="Mesothelae"
label2 = "Opisthothelae"
2 = clade
label1 =
1 = "Mygalomorphae"
2 = "Araneomorphae"

Almost 40,000 species of spiders (order "Araneae") have been identified and are currently grouped into 111 families by arachnologists, but because of difficulties in collecting these often very minute and evasive animals, and because of many specimens stored in collections waiting to be described and classified, it is believed that up to 200,000 species may exist.

The order is composed of three suborders. In the non-venomous primitive "Mesothelae", body segmentation is clearly visible, demonstrating the link of spiders with their segmented arthropod ancestors.

The two other suborders, the "Mygalomorphae" (trapdoor spiders, funnel-web spiders, tarantulas) and the "Araneomorphae" ("modern" spiders), are sometimes grouped together as "Opisthothelae". The latter account for about 94% of all spider species.

Mesothelae

The Mesothelae include the only recent family Liphistiidae. Two more families (Arthrolycosidae and Arthromygalidae) are recognized from fossil evidence only.

The Liphistiidae are burrowing spiders only found in Southeast Asia, China, and Japan with about 90 species in 5 genera. Spiders of this remnant suborder are very rare, and are among the most "primitive" types of spiders in existence.

Recent Mesothelae are characterized by the narrow sternum on the ventral side of the prosoma. Several plesiomorphic characters may be useful in recognizing these spiders: there are tergite plates on the dorsal side and the almost-median position of the spinnerets on the ventral side of the opisthosoma.

Mygalomorphae

The Mygalomorphae are also called the Orthognatha, referring to the orientation of the fangs roughly in line with the body axis. This suborder includes the heavy bodied, stout legged spiders popularly known as tarantulas as well as the dangerous Australasian funnel-web spiders. They have ample venom glands that lie entirely within their chelicerae. Their chelicerae and fangs are large and powerful. Occasionally members of this suborder will even kill small fish, small mammals, etc. Most members of this suborder occur in the tropics and subtropics, but their range can extend farther toward the poles, e.g. into the southern and western regions of the United States and Canada, the northern parts of Europe and south into Argentina and Chile.

Araneomorphae

The Araneomorphae, (previously called the Labidognatha), are often known as the "modern spiders".

Araneomorphae are distinguished by fangs that move at a 90 degree angle to the body axis, like a pair of pincers. Most of the spiders that people encounter in daily life belong to this suborder, which makes up 94% of all spider species.

There are approximately 95 families in this suborder, ranging from the minute "Patu digua" (0.37 mm) to the big and flashy "Argiope", from the common orb-weaver spiders to the abstruse assassin spiders, from the reclusive tree trapdoor spiders to the inquisitive jumping spiders.

Creatures often mistaken for spiders

In addition to the true spiders, there are several arachnids commonly mistaken for spiders, but that are not true spiders.
*Camel spider, a species of solifugid (also commonly called sun-spiders or wind-scorpions), are the source of many urban legends. Although they have no venom the camel spider has been known to attack humans, focusing on exposed skin, and with fangs capable of tearing human flesh. Several myths surround camel spiders, and their size is usually exaggerated. While they are really the size of an adult human hand, myths tell they are as large as the lower half of an adult human leg. Also, they are harmless to humans, and will only attack if disturbed.
*The daddy long-legs or harvestman is a member of the order Opiliones. These round-bodied arachnids have only two eyes and their heads are fused to their bodies. However, the name "daddy long-legs" is sometimes used to refer to cellar spiders, which have a similar leg shape; these are true spiders. Both are also often said to produce a deadly venom. While the harvestmen do not produce venom at all, the cellar spider's venom is completely harmless to humans. The term daddy long-legs is also used in British English to refer to the Crane fly, which is an insect and not an arachnid at all.

piders and people

pider bites

Most spiders will only bite humans in self-defense, and few produce worse effects than a mosquito bite or bee-sting. [cite web
title=Spiders | publisher=Illinois Department of Public Health
url=http://www.idph.state.il.us/envhealth/pcspiders.htm | accessdate=2008-10-11 ] Most of those with medically serious bites, such as recluse spiders and widow spiders, are shy and bite only when they feel threatened, although this can easily arise by accident.cite journal | author = Vetter R, Barger D | title = An infestation of 2,055 brown recluse spiders (Araneae: Sicariidae) and no envenomations in a Kansas home: implications for bite diagnoses in nonendemic areas | journal = J Med Entomol | volume = 39 | issue = 6 | pages = 948–51 | year = 2002 | pmid = ] [cite web
title=Widow Spiders | author=Hannum, C.and Miller, D.M.
publisher=Department of Entomology, Virginia Tech
url=http://www.ext.vt.edu/pubs/entomology/444-422/444-422.html | accessdate=2008-10-11 ] Funnel web spiders' defensive tactics are aggressive, although they rarely inject much venom. [cite web
url=http://www.avru.org/compendium/biogs/A000003b.htm | accessdate=2008-10-11
title=Funnel web spiders | publisher=Australian Venom Research Unit] On the other hand the Brazilian wandering spider requires very little provocation. [cite web
url=http://news.bbc.co.uk/1/hi/england/somerset/4489033.stm | accessdate=2008-10-11
title=Pub chef bitten by deadly spider | publisher=BBC ] There were about 100 reliably reported deaths from spider bites in the 20th century, [cite journal
author=Diaz, J.H.
title=The Global Epidemiology, Syndromic Classification, Management, and Prevention of Spider Bites
journal=American Journal of Tropical Medicine and Hygiene | volume=71 | issue=2 | date=2004 | pages=239-250
url=http://www.ajtmh.org/cgi/content/abstract/71/2/239 | accessdate=2008-10-11 ] but about 1,500 from jellyfish stings.cite book
author=Williamson, J.A., Fenner, P.J., Burnett, J.W., and Rifkin, J.
title=Venomous and Poisonous Marine Animals: A Medical and Biological Handbook
publisher=UNSW Press | date=1996 | isbn=0868402796 | pages=65-68
url=http://books.google.co.uk/books?id=YsZ3GryFIzEC&pg=PA75&lpg=PA75&dq=mollusc+venom+fatal&source=web&ots=tBDHW2xdlx&sig=PAvTz2z3hnwUyE4lfU8fvzwNbD4&hl=en&sa=X&oi=book_result&resnum=2&ct=result#PPA57,M1 | accessdate=2008-10-03] Many alleged cases of spider bites may represent incorrect diagnoses, [cite journal
author=Nishioka, S de A. | title=Misdiagnosis of brown recluse spider bite
journal=Western Journal of Medicine | date=August 2001 | volume=175 | issue=2 | page=240
url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1071491 | accessdate=2008-10-03 ] which would make it more difficult to check the effectiveness of treatments for genuine bites. [cite journal
author=Isbister, G.K. | title=Spider mythology across the world
journal=Western Journal of Medicine | date=April 2001 | volume=174 | issue=4 | pages=86–87
url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1071344 | accessdate=2008-10-03 ]

Benefits to humans

Cooked tarantula spiders are considered a delicacy in Cambodia, [cite book
author=Ray, N. | date=2002 | title=Lonely Planet Cambodia | publisher=Lonely Planet Publications
isbn=1-74059-111-9 | page=308 ] and by the Piaroa Indians of southern Venezuela – provided the highly irritant hairs, the spiders' main defense system, are removed first. [cite book
author=Weil, C. | title=Fierce Food | date=2006 | publisher=Plume | isbn=0452287006
url=http://www.budgettravel.com/bt-dyn/content/article/2006/10/24/AR2006102400797.html
accessdate=2008-10-03 ]

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. [cite web
title=Spider Venom Could Yield Eco-Friendly Insecticides | publisher=National Science Foundation (USA)
url=http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=100676&org=NSF | accessdate=2008-10-11 ]

Possible medical uses for spider venoms are being investigated, for the treatment of cardiac arrhythmia, [cite journal
author=Novak, K. | title=Spider venom helps hearts keep their rhythm
journal=Nature Medicine | volume=7 | issue=155 | date=2001 | doi=doi:10.1038/84588 ] Alzheimer's disease, [cite journal
author=Lewis, R.J., and Garcia, M.L. | title=Therapeutic potential of venom peptides
journal=Nature Reviews Drug Discovery | volume=2 | pages=790-802 | date=October 2003 | doi=10.1038/nrd1197
url=http://imb.uq.edu.au/download/large/Venom_therapeutics.pdf | accessdate=2008-10-11 ] strokes, [cite journal
author=Bogin, O.
title=Venom Peptides and their Mimetics as Potential Drugs
journal= Modulator | issue=19 | date=Spring 2005
url=http://www.alomone.com/System/UpLoadFiles/DGallery/Docs/Venom%20Peptides%20and%20their%20Mimetics%20as%20Potential%20Drugs.pdf
accessdate=2008-10-11 ] and erectile dysfunction. [cite journal
author=Andrade, E., Villanova, F., Borra, P., "et al"
title=Penile erection induced "in vivo" by a purified toxin from the Brazilian spider "Phoneutria nigriventer"
journal=British Journal of Urology International | volume=102 | issue=7 | pages=835-837 | June 2008
doi=10.1111/j.1464-410X.2008.07762.x ]

Although spiders are feared and disliked by many, they benefit humankind by destroying many insects pests such as fly, mosquitoes, grasshoppers, locusts, cockroaches, and aphids.Fact|date=October 2008

Arachnophobia

Arachnophobia is a specific phobia, an abnormal fear of spiders or anything reminiscent of spiders, such as webs or spider-like shapes. It may be an exaggerated form of an instinctive response that helped early humans to survive, [cite book
author=Friedenberg, J., and Silverman, G. | title=Cognitive Science: An Introduction to the Study of Mind

publisher=SAGE | date=2005 | isbn=1412925681 |pages=244-245

url=http://books.google.co.uk/books?id=wGti6_4Qn_QC&pg=PA244&dq=Arachnophobia&lr=&sig=ACfU3U2bQYuqAO7EUfWM6MCqFu-Jy-COAA#PPA244,M1
accessdate= 2008-10-11 ] or perhaps a cultural phenomenon that is most common in predominantly Euporean societies. [cite journal
author=Davey, G.C.L.
title=The “Disgusting” Spider: The Role of Disease and Illness in the Perpetuation of Fear of Spiders
journal=Society and Animals | volume=2 | issue=1 | date=1994 | pages=17-25 | doi=10.1163/156853094X00045 ]

"Arachnophobia" is also the title of a 1990 film, as well as a spin-off video game, in which fictitious deadly spiders overrun a small California town. [cite book
editor=Maltin, L., and Edelman, R. | title=Leonard Maltin's Movie and Video Guide 2002
publisher=Signet | date=2002 | isbn=9780451203922 | page=58 ] [cite web
url=http://uk.pc.ign.com/objects/008/008412.html | accessdate=2008-10-11
title=IGN: Arachnophobia]

piders in symbolism and culture

Spiders have been the focus of fears, stories and mythologies of various cultures for centuries. [cite book|last=De Vos|first=Gail|title=Tales, Rumors, and Gossip: Exploring Contemporary Folk Literature in Grades 7-12|publisher=Libraries Unlimited|year=1996|pages=186|isbn=1563081903|url=http://books.google.com/books?id=M8bvN93y-fIC&pg=PA186&dq=spiders+folklore+and+mythology&lr=&ei=HHsNSNGgNZOKsgO2sqnHAQ&sig=rfYxr-r7pktGmHuA31vEUL99rn8|accessdate=2008-04-22] They have symbolized patience due to their hunting technique of setting webs and waiting for prey, as well as mischief and malice for the painful death their venom causes.cite book |last=Garai |first=Jana |title=The Book of Symbols |year=1973 |publisher=Simon & Schuster |location=New York |isbn=671-21773-9] Web-spinning also caused the association of the spider with creation myths as they seem to have the ability to produce their own worlds. [cite book|last=De Laguna et al|first=Frederica|title=American Anthropology: Papers from the American Anthropologist|publisher=University of Nebraska Press|year=2002|pages=455|isbn=080328280X|url=http://books.google.com/books?id=XIFX-sSYURwC&pg=PA455&dq=Spider+creation+myth&sig=RI0W9BNC-E36_Le7G2bMvhbjQNw|accessdate=2008-04-21] The Moche people of ancient Peru worshipped nature. [ Benson, Elizabeth, The Mochica: A Culture of Peru. New York, NY: Praeger Press. 1972] They placed emphasis on animals and often depicted spiders in their art. [Berrin, Katherine & Larco Museum. "The Spirit of Ancient Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera." New York: Thames and Hudson, 1997.]

ee also

*Endangered spiders
*Identifying spiders
*Spider diversity
*Spider-Man
*Spider webs in space

Footnotes

References

*Bilger, Burkhard. "Spider Woman". "The New Yorker", 5 March 2007, pp. 66–73.
*cite book|title=The World of Spiders|author=W. S. Bristowe|publisher=Taplinger Pub Co|id=ISBN 0-8008-8598-8|year=1976
*Crompton, John. "The Life of the Spider", Mentor, 1950.
*Hillyard, Paul. "The Book of the Spider", Random House, New York, 1994.
*Kaston, B. J. "How to Know the Spiders", Dubuque, 1953.
*Main, Barbara York. "Spiders", Collins (The Australian Naturalist Library), Sydney, 1976.
*Ubick, Darrell; Pierre Paquin, Paula E. Cushing, and Vincent Roth. "Spiders of North America: an Identification Manual", American Arachnological Society, 2005.
*Wise, David H. "Spiders in Ecological Webs." Cambridge University Press. Great Britain: 1993.

External links

General

* [http://www.arachnology.be/pages/Araneae.html Arachnology Home Page: Araneae — Spiders]
* [http://www.dearge.de/english.php Deutsche Arachnologische Gesellschaft e. V. — German Arachnologic Society (EN/DE)]
* [http://www.uos.harvard.edu/ehs/pes_spiders.shtml Indoor Spiders of New England] Harvard University
* [http://www.xs4all.nl/~ednieuw/Spiders/InfoNed/The_spider.html Spider info by Ed Nieuwenhuys]
* [http://npic.orst.edu/pest2.htm#spiders Spider Pest Control Information — National Pesticide Information Center]
* [http://vector.ifas.ufl.edu/chapter_07.htm Venomous Arthropods] chapter in EPA and UF / IFAS National Public Health Pesticide Applicator Training Manual
*Spider webs in space
*Wikia|spiders

Regional

* [http://www.amonline.net.au/spiders/ Australian spiders]
* [http://www.pavouci-cz.eu/pavouci.php Czech spiders with photos]
* [http://www.aranhas.info Portuguese spiders]
* [http://www.britishspiders.org.uk/ Spiders found in Great Britain]
* [http://caucasus-spiders.info/ Spiders of the Caucasus (caucasus-spiders.info)]
* [http://spiders.entomology.wisc.edu/ Spiders of Wisconsin]
* [http://www.usq.edu.au/spider/index.htm University of Southern Queensland's Find-a-spider guide]
* [http://delta-intkey.com/britsp Watson, L., and Dallwitz, M.J. 2004 onwards. The families of spiders represented in the British Isles.]

Morphology

* [http://www.users.qwest.net/~phidippus/page10.htm Histology of Salticid Spiders]

Taxonomy

* [http://www.canadianarachnology.org Canadian Arachnologist & Nearctic Spider Database]
*aut|Platnick, Norman I. (2008): [http://research.amnh.org/entomology/spiders/catalog/index.html The world spider catalog] , version 8.5. "American Museum of Natural History".
* [http://research.amnh.org/entomology/spiders/catalog/COUNTS.html Total number of described spider genera and species]

Pictures

* [http://www.free-nature-photos.org/en/Spiders/ Free Nature Photos, spiders]
* [http://www.macro-photo.org/species-checklist-arthropods-insects-birds-avians/spiders-araneae-macro-photo-images-gallery.htm Macro Photography - Pictures of spiders, image gallery] (commercial, but very good pictures)
* [http://www.badspiderbites.com/spider-identification.php Photos of spiders from around the world.]
* [http://www.cirrusimage.com/spider.htm Spiders of North America] Library of reference quality large format photographs with taxonomy and descriptions.
* [http://www.tarantulas.us/gallery/ Tarantulas.us - Gallery] — The largest photo gallery of all tarantula's species.

Other

* [http://www.sciencedaily.com/news/plants_animals/spiders/ Spiders] Research on Spiders from Science Daily.
* [http://www.tarantulatour.com Tarantula Tour]
* [http://spiders.ucr.edu/dermatol.html University of California evaluations of spider bite severity]
* [http://www.cannabis.net/weblife.html Webs made by spiders fed on drug-dosed flies]