However, despite these examples and many other similar reports, the theory of the 'sacrificial male' has become greater than the truth. Mating of spiders is not always followed by cannibalism. Foelix writes, "The supposed aggressiveness of the female spider towards the male is largely a myth... only in some exceptional cases does the male fall victim to the female." Foelix, Rainer F. Biology of Spiders, 1982. Michael Roberts says, "It is rare for a fit male to be eaten by the female."Roberts, Michael J. Spiders of Britain and Northern Europe, Collins, London, 1995. And yet, spider cannibalism has been proved to occur in some species more than in others, mainly species belonging to Latrodectus.

There has always been speculation on why this sacrifice of male mates might occur despite the fact that there is an obvious disadvantage to the sacrificial males. One theory is that once the male has mated, he is unlikely to mate again and so any further extension of his life serves no evolutionary purpose, while the sacrifice of the male may help increase egg production and offspring viability through increased nutrition provided to the female. Having more offspring would give the male the advantage of having his genes passed on over other males that might avoid being eaten. This scenario would be consistent with the hypothesis of Roberts that old or unfit males get eaten, whilst younger and fitter ones may survive to mate again.

Ecology

While spiders are generalist predators, in actuality their different methods of prey capture often determine the type of prey taken. 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. Groups of families that tend to take certain types of prey because of their prey capture methods are often called guilds. 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. Bolas spiders in the family Araneidae use sex pheromone analogs to capture only the males of certain moth species. Despite their generally broad prey ranges, spiders are one of the most important links in the regulation of the populations of insects. Every day on a meadow they devour over 10 g/m² of insects and other arthropods.

Predatory techniques

There are many families of spiders, and the ways that they catch prey are diverse. But whether they catch insects, fish, small mammals, small birds, or some other small form of life, as soon as a spider makes contact with its prey it will generally attempt to bite it.

Spiders bite their prey, and occasionally animals that cause them pain or threaten them, to do two things. First, they inflict mechanical damage, which, in the case of a spider that is as large as or larger than its prey, can be severe. Second, they can choose to inject venom through their hollow fangs. Many genera, such as the widow spiders, inject neurotoxins that can spread through the prey's entire body and interfere with vital body functions. Other genera inject venom that operates to produce tissue damage at the site of the bite. Genera such as that of the brown recluse spider produce a necrotoxin. The necrotoxin is injected into prey where it causes the degradation of cell membranes. In the larger victims that do not die from these attacks, painful lesions over a fairly wide area of the body can remain active for fairly long periods of time. The spitting spiders have modified their poison glands to produce a mixture of venom and sticky substance that works as glue and immobilise the prey.

Digestion is carried out internally and externally. Spiders that do not have powerful chelicerae secrete digestive fluids into their prey from a series of ducts perforating their chelicerae. These digestive fluids dissolve the prey's internal tissues. Then the spider feeds by sucking the partially digested fluids out. Other spiders with more powerfully built chelicerae masticate the entire body of their prey and leave behind only a relatively small glob of indigestible materials. Spiders consume only liquid foods. Many spiders will store prey temporarily. Web weaving spiders that have made a shroud of silk to quiet their envenomed prey's death struggles will generally leave them in these shrouds and then consume them at their leisure.

Although there are no vegetarian spiders, some species in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae have been observed feeding on plant nectarJackson, R.R. et. al. (2001). Jumping spiders (Araneae: Salticidae) that feed on nectar. ''J. Zool. Lond. 255:25-29 PDF. Several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages in captivity.

Spider webs and prey capture

Some spiders spin funnel-shaped webs, others make sheet webs, spiders like the black widow make tangled, maze-like, webs, and still others make the spiral "orb" webs that are most commonly associated with spiders. These webs may be made with sticky capture silk, or with "fluffy" capture silk, depending on the type of spider. Webs may be in a vertical plane (most orb webs), a horizontal plane (sheet webs), or at any angle in between. Most commonly found in the sheet-web spider families, some webs will have loose, irregular tangles of silk above them. These tangled obstacle courses serve to disorient and knock down flying insects, making them more vulnerable to being trapped on the web below. They may also help to protect the spider from aerial predators such as birds and wasps.

The spider, after spinning its web, will then wait on, or near, the web for a prey animal to become trapped. The spider can sense the impact and struggle of a prey animal by vibrations transmitted along the web lines.

Other species of spiders do not use webs for capturing prey directly, instead pouncing from concealment (e.g. trapdoor spiders) or running them down in open chase (e.g. wolf spiders). The net-casting spider balances the two methods of running and web-spinning in its feeding habits. This spider weaves a small net which it attaches to its front legs. It then lurks in wait for potential prey and, when such prey arrives, lunges forward to wrap its victim in the net, bite and paralyze it. Hence, this spider expends less energy catching prey than a primitive hunter such as the Wolf spider. It also avoids the energy cost of weaving a large orb-web. The diving bell spider has even modified its web into an underwater diving bell, and is no longer used for prey capture. Even species whose ancestors were building spiral orb webs have given rise to spiders who no longer makes a web, for instance some Hawaiian spiny-legged spiders (genus Tetragnatha, family Tetragnathidae) which have abandoned web construction entirely.

Some spiders manage to use the 'signaling snare' technique of a web without spinning a web at all. Several types of water-dwelling spiders will rest their feet on the water's surface in much the same manner as an orb-web user. When an insect falls onto the water and is ensnared by surface tension, the spider can detect the vibrations and run out to capture the prey.

Defense

Social spiders

Evolution

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 first known fossil spider, Attercopus, lived 380 million years ago during the Devonian. Attercopus is placed as sister-taxon to all living spiders, on the basis of characters of the spinneret and the arrangement of the patella­tibia joint of the walking legs. Graeophonus, another genus of early spider, lived over 300 million years ago during the Carboniferous.

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. They were probably ground dwelling predators, living in the giant clubmoss and fern forests of the mid-late Palaeozoic, where they were presumably 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 (Suborder Opisthothelae with infraorders 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. The oldest mygalomorph, Rosamygale, was described from the Triassic of France and belongs to the modern family Hexathelidae. Megarachne servinei from the Permo-Carboniferous was once thought to be a giant mygalomorph spider and, with its body length of 1 foot (34 cm) and leg span of above 20 inches (50 cm), the largest known spider ever to have lived on Earth, but subsequent examination by an expert revealed that it was actually a middling-sized sea scorpion.

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, the most famous, circular kind one thinks of when imagining spider webs. Additional genetic evidence suggests, by examining the drift of genes thought to be used to produce the web-spinning behavior, suggest that orb spinning was in an advanced state as many as 136 million years ago.

The 110 million year old amber-preserved web is also the oldest to show trapped insects, containing a beetle, mite, wasp's leg, and fly. 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.

Types of spiders

The order Araneae is composed of two sub-orders: the Mesothelae, which contains the present family Liphistiidae, primitive burrowing spiders from Asia, and the Opisthothelae, which contains the vast majority of spiders. Opisthothelae is further divided up into two infraorders, the Mygalomorphae (trapdoor spiders, funnel-web spiders, and tarantulas) and Araneomorphae (the modern spiders). The largest clade of araneomorph spiders is the Entelegynae.

Over 38,000 species of spiders have been identified, but because of their great ability for hiding, it is believed that about 200,000 species exist. All species of spider posess venom (with the exception of the families Uloboridae and Heptthelidae), but only 40 species are known to be potentially deadly to humans.

For a guide to identifying spiders, see Spider finder (under construction)

Mesothelae

Mesothelae is one suborder of spiders that include the families Liphistiidae, Arthrolycosidae, and Arthromygalidae. The latter two families are known only from fossil records; there are no living specimens of either family. Family Liphistiidae comprises 5 genera and 87 species, found in Southeast Asia, China, and Japan. Spiders of this 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, (also called the Orthognatha), are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other (cf araneomorph). 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 poison 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 infraorder 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. They are distinguished by having chelicerae that point diagonally forward and cross in a pinching action, in contrast to the Mygalomorphae (tarantulas and their close kin), where they point straight down. Most of the spiders that people encounter in daily life belong to this suborder.

There are approximately 50 families in this suborder.

Tangleweb spiders (Theridiidae)

=Widow spiders

Widow spider (Latrodectus spp.) are a large, cosmopolitan group; all with relatively dangerous bites. These are relatively large, 1/2 inch long. The bodies of the females are 'burly-looking'. They are generally dark, typically glossy black, and generally have a red mark on the glossy, smooth abdomen, on either its top or bottom surface. There are several species of Latrodectus, some with lighter overall coloration. They are all highly venomous, though the various "brown" species (L. geometricus, L. rhodenesies) are somewhat less so than the "black" varieties.

Examples of widow spiders include

• Black widow spiders (Latrodectus spp.) of North America
• Latrodectus tredecimguttatus, known as the European or Mediterranean black widow, the malmignatte spider, or the karakurt spider
• Red-back spider of Australia, now found throughout Asia
• Red katipo and black katipo spiders of New Zealand
• Button spiders of southern Africa
• Brown widow spider, found worldwide
• Red widow spider, found in Florida
• White widow spider, found in the Middle East and southwest Asia

=Steatoda

The genus Steatoda is a large genus which includes many of the false black widows, as well as other types of cobweb spiders. Many specimens in this genus are sometimes mistaken for widows, but they have more flattened abdomens, and their abdominal markings are generally white stripes or dots rather than red dots. None of these spiders is truly dangerous, but some of them are medically significant, including:

• S. grossa
• S. nobilis
• S. paykulliana

=Other tangle-web spiders

Others are characterized by large, globular abdomens, thin, spindly legs. Often they display rather non-descript patterns in gray or brown and white. Examples:

• American house spider (not dangerous)

Orb web spiders (Araneidae)

Examples include:

• St Andrew's Cross spider (an Argiope)
• Long-jawed orb weaver Tetragnathidae
• Cyclosa conica
• Golden silk orb-weaver
• European garden spider
• Australian garden orb weaver spider
• Jewel spider
• Spined Micrathena Micrathena gracilis

Other forms of webs

This category is a "catch-all" comprising members of several different groups that spin non-sticky webs in a variety of structural styles. 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 (with one notable exception - the Hobo spider, below). 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.

• Sydney funnel-web spider (Atrax robustus) (extremely dangerous)
• Atypidae. (not dangerous)
• Bowl-and-doily spiders (Linyphiidae) (not dangerous)
• Hobo spider (Tegenaria agrestis) (dangerous)
• Grass spiders (Agelenidae) (not dangerous)
• Filmy dome spider (Linyphiidae) (not dangerous)
• Hackled orb-weaver (no venom)
• Net-casting spider (not dangerous)

Hunting spiders

• Brazilian wandering spider (extremely dangerous)
• Brown recluse spider (very dangerous)
• Huntsman spiders (painful bites)
• Jumping spiders (not dangerous)
• Lynx spiders (not dangerous)
• Nursery web spiders (not dangerous)
• Spitting spiders (not dangerous)
• Tarantulas (painful bites; some species like the Chinese bird spider may be dangerous)
• Wolf spiders (Lycosidae) (not dangerous; bites of one species in S. America produces some tissue necrosis)
• Yellow sac spider (painful bites - may produce effects like a milder form of Recluse venom)

Assassin Spiders:

• Assassin spiders are hunting spiders that prey on other spiders. Though relatively small, they are regarded as some of the most deadly spiders alive due to there evolved hunting techiques. Assissin spiders are not large enough to cause any serious injury to humans.

• though fossil records indicate that assissin spider were once common all over the world, they are now primarily found in Africa, Austraila, and Madagascar.

Spiders that ambush their prey

This is another catch-all category that includes a diverse collection of spiders. Some actively lure prey (the Bolas spiders) and may capture them with a sticky ball of silk on a line; others wait in a high-traffic area and directly attack their prey from ambush.

• Six-eyed sand spider (Sicariidae) (extremely dangerous)
• Trapdoor spider (painful bites)
• Crab spiders (Thomisidae) (not dangerous)
• Bolas spiders (Araneidae) (not dangerous)

Other spiders

• Kimura-gumo (Heptathela kimurai, a member of the Family Liphistiomorphae) (not dangerous)
• Spruce-fir moss spider, Microhexura montivaga
• Tooth cave spider, Neoleptoneta myopica
• Bird dropping spider, Celaenia excavata

Creatures often mistaken for spiders

• Camel spider, not actually a spider at all, but rather a solifugid (also commonly called sun-spiders or wind-scorpions). Very well known as the source of many urban legends (no venom)
• 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 but not dangerous.

Spider bites

Most spiders are unlikely to bite humans because they do not identify humans as prey. Spiders, even small ones, may however bite humans when pinched. For instance, a common jumping spider (Family: Salticidae), around 3/8 inch (1 cm) long, when pinched between the folds of a human's palm may inflict a bite that is about as painful as a bee sting.

Spiders in the world which have been linked to fatalities in humans, or have been shown to have potentially fatal bites by toxicology studies of their venom, include:

• The Brazilian wandering spider
• The Australasian funnel-web spider
• The Six-eyed sand spider, and possibly other spiders of genus Sicarius
• The widow spiders
• The recluse spiders

Spiders which likely are not deadly to humans, but which are nonetheless medically significant include:

• The hobo spider
• The yellow sac spider
• Certain species of tarantulas
• The false black widows

Spiders which can inflict painful bites (often similar to a bee sting), but whose bites generally do not cause any systemic or long-lasting effects, include:

• The huntsman spider
• The redback jumping spider (not to be confused with the very dangerous redback spider, the latter being one of the widow spiders).

None of these spiders will intentionally "come after you," but they should be removed from one's house to avoid accidental injury. Many authorities warn against spraying poisons indiscriminately to kill all spiders, because doing so may actually remove one of the biological controls against incursions of the more dangerous species by ridding them of their competition.

If dangerous spiders are present in your area, be mindful when moving cardboard boxes and other such objects that may have become the shelter of a poisonous spider. There is no need to be fearful; just do not grab a spider.

Spiders in symbolism and culture

• Many techniques (fictional and otherwise) of ninja are named after spiders, usually due to involving spiderlike movement or other traits.
• The Italian dance and music tarantella is related to tarantulas, either as a folk remedy for bites or from its vigorous movements.
• Spider is the stage name of an American songwriter and producer from Los Angeles.

In folklore

• Arachne, a weaver turned spider in Greek mythology.
• Anansi is a famous character from African folklore, often depicted as a spider. Anansi is also known as:
  • Kwaku Ananse, the West African trickster.
  • Aunt Nancy (or Sister Nancy), a variant specifically found in some of the islands of the West Indies, but also in South America and the United States.
  • Bouki and Ti Malice, Anansi adventures in Haiti.
• A famous legend, probably apocryphal. states that King Robert the Bruce of Scotland, when fighting the English, took refuge in a cave after a series of military failures. In the cave he saw a spider, which after repeatedly failing to weave its web, eventually succeeded due to perseverance. The moral of the story is "try, try and try again". Bruce eventually won Scotland's independence, and many places claim the cave, most notably Rathlin island.

In literature

• Charlotte's Web is a 1952 children's novel by E. B. White about an intelligent farm spider whose machinations save a young pig from the slaughterhouse.
• The novel Web by John Wyndham is set on an island populated by spiders that have developed a co-operative social structure similar to ants.
• Shelob is a giant spider-like creature in the Lord of the Rings saga.
• Spider Boys (ISBN 068812858) is a novel by Ming Cher. Written in the fractured but vibrant English of street kids in Singapore, the kids capture, nurture, sell, and send into combat the male jumping spiders indigenous to that clime.
• In Harry Potter and the Chamber of Secrets by J. K. Rowling, Hagrid's pet Aragog is a giant spider, which then runs away to live in the forest.

In comics, manga, and cartoons

• Spider-Man is a Marvel Comics character with spider-like powers, created by writer Stan Lee and artist Steve Ditko. Spider-Man was originally a young student who becomes a superhero after being bitten by a "radioactive spider" and gaining superhuman abilities. Several derivative characters have also been developed, including Spider-Woman and Spiderboy. Spider-Man's avatars include Pavitr Prabhakar, his Indian version, and Yu Komori, his manga version.
  • Spider-Man (2002) is a feature film, directed by Sam Raimi and starring Tobey Maguire, Willem Dafoe, and Kirsten Dunst. Spider-Man 2 (2004) is a sequel, and Spider-Man 3 (2007) is a planned second sequel.
  • See Spider-Man (disambiguation) for other references and works based on the Spider-Man character.
• Spinarak and Ariados are spider-like monsters from the Pokémon franchise.
• Anansi the Spider is a superhero in the Static Shock animated series.

In motion pictures

• Arachnophobia (named for arachnophobia, fear of spiders) is a 1990 movie directed by Frank Marshall, in which spiders multiply in large numbers and kill humans. The movie inspired a video game of the same name, developed by BlueSky Software and Disney for the DOS and Commodore 64 platforms.
• Spider! is a 1998 feature film in which a giant spider comes from outer space through a shuttle which is sent on an outer space mission. Once the Spider arrives on Earth, it eats human beings, and uses their bodies to lay eggs, and more spiders come out of the human body.
• Eight Legged Freaks is a 2002 feature film in which spiders get mutated because of harmful nuclear waste in mines and hence become over-sized creatures and hunt humans.
• Kingdom of the Spiders (1977) is a feature film starring William Shatner as a veterinarian forced to deal with spiders after the spiders' normal food sources were destroyed by heavy use of pesticides.
• In Jumanji (1995), one of the group of creatures which appears is a group of giant spiders.
• A famous deleted scene from the 1933 version of King Kong is called "the spider pit scene". In this scene, several sailors are chased by King Kong onto a log lying over a fissure. Kong starts to shake the sailors off the log, until he finally drops the log down the fissure. The surviving sailors are eaten alive by giant bugs, including a spider. This scene was taken out of the film because it was too shocking. This scene has not yet been found, although many film experts are hunting for it. A similar scene was used in the 2005 remake, although it contained no spiders.

See also

• List of images/Nature/Animals/Spiders

References