• The spider

Spider

This article is about the spider, the animal. For other article subjects named spider see Spider (disambiguation).

Spiders
Long-jawed Orb Weaver, #redirect : Tetragnathidae #redirect : Tetragnatha
#redirect
#redirect : Animalia #redirect : Arthropoda #redirect : Arachnida #redirect : Araneae
Families
Suborder Mesothelae     Liphistiidae (primitive burrowing spiders) Suborder Mygalomorphae     Atypidae (atypical tarantula)     Antrodiaetidae (folding trapdoor spider)     Mecicobothriidae (dwarf tarantulas)     Hexathelidae (venomous funnel-web tarantula)     Dipluridae (funnel-web tarantula)     Cyrtaucheniidae (wafer trapdoor spider)     Ctenizidae (trapdoor spider)     Theraphosidae (tarantula) Suborder Araneomorphae     Hypochilidae (lampshade spider)     Filistatidae (crevice weaver)     Sicariidae (recluse spider)     Scytodidae (spitting spider)     Leptonetidae (leptonetid spider)     Pholcidae (daddy long-legs spider)     Plectreuridae (plectreurid spider)     Diguetidae (coneweb spider)     Caponiidae (two-eyed spider)     Segestriidae (tube-dwelling spider)     Dysderidae (woodlouse hunter spider)     Oonopidae (oonopid spider)     Palpimanidae (palp-footed spider)     Mimetidae (pirate spider)     Eresidae (velvet spider)     Oecobiidae (including Urocteidae)     (wall and six-exit tent spider)     Hersiliiidae (tree trunk spider)     Deinopidae (ogre-faced spider)     Uloboridae (cribellate orb and         sector weaver spider)     Nesticidae (scaffold web spider)     Theridiidae (tangle web spider)     Linyphiidae (bowl and doily and         dwarf spiders)     Tetragnathidae (long jawed spider)     Araneidae (orb-weaver spider)     Lycosidae (wolf spider)     Pisauridae (nursery web spider)     Oxyopidae (lynx spider)     Zorocratidae (zorocratid spider)     Zoropsidae (zoropsid spider)     Ctenidae (wandering spider)     Agelenidae (araneomorph funnel-web spider)     Cybaeidae (water spider)     Desidae (intertidal spider)     Hahniidae (dwarf sheet spider)     Dictynidae (dictynid spider)     Amaurobiidae (tangled nest spider)     Titanoecidae (titanoecid spider)     Tengellidae (tengellid spider)     Miturgidae (long-legged sac spider)     Anyphaenidae (anyphaenid sac spider)     Liocranidae (liocranid sac spider)     Clubionidae (sac spider)     Corinnidae (corinnid sac spider)     Zodariidae (zodariid ground spider)     Gnaphosidae (ground spiders)     Selenopidae (wall crab spider)     Sparassidae (huntsman, etc.)     Philodromidae (philodromid crab spider)     Thomisidae (crab spider)     Salticidae (jumping spider)
Source: Platnick 2003

Many spiders hunt by building webs to trap insects. These webs are made of spider silk, a thin, strong protein strand extruded by the spider from spinnerets on the end of the abdomen. All spiders produce silk, although not all use it to spin elaborate traps. Silk can be used to aid in climbing, forming smooth walls for burrows, cocooning prey, and for many other applications.

Table of contents

1 Anatomy 2 Reproduction 3 Life cycle 4 Ecology 4.1 Predatory techniques 4.2 Spider webs and prey capture 5 Types of spiders 5.3 Tangleweb spiders 5.4 Orb weavers 5.5 Other forms of webs 5.6 Spiders that live on flowers 5.7 Hunting spiders 5.8 Others 6 Spider bites 6.9 Black widows 6.10 Brown recluse spiders 6.11 Huntsman spiders 6.12 Redback jumping spiders 6.13 Brazilian wandering spiders and Sydney funnel-web spiders 7 Further reading 8 External links

Anatomy

Eyes can be arranged differently in different species. Sometimes one pair is better developed than the rest. Some species have a pair less or are even without eyes. While several families of hunting spiders have good to excellent vision (Lycosidae and Salticidae), the members of most families of hunting spiders, most of the web weavers and the spiders that lurk on flowers and other fixed locations waiting for some insect to come their way have very poor eyesight. Instead, these spiders hunt using their extreme sensitivity to vibrations.

Unlike insects, spiders have no feelers. Instead, they have pedipalps, sometimes just called palps, which are two additional appendages next to their mouth parts that, besides having other functions, they use to help themselves manipulate the food that they eat.

Spider haemolymph (the equivalent of blood) does not circulate through vessels, but just fills the body of the spider. This is called an open circulatory system. The spider's respiratory anatomy is based on a tracheal system, with each opening to the trachea as an extension of an outer pore reaching from the spider abdomen, protected by spiracles which are pores in the spider exoskeleton, composed of chitin.

Book lungs alone, respiratory organs with openings on the ventral surface of the abdomen, enrich the blood of primitive mygalomorph spiders with oxygen, and araneomorph spiders use spiracles as well. The latter are much more efficient and allow more advanced characteristics to be displayed, such as cursorial hunting (hunting involving rapid pursuit).

Reproduction

The male Latrodectus hasselti actually dies after it inserts its second palpus in the female genital opening even if the female does not eat it. The three species of North American black widows do not seem to require the death of the male (although it may occur) and males can sometimes live in the web of a female for a while without being harmed. There has been much speculation on why the sacrifice of male mates is so common, but it may simply be that female spiders tend not to discriminate between male spiders of their species and other similar small arthropods that are their normal prey.

Spiders often use elaborate mating rituals (especially in the visually advanced jumping spiders) to allow the male to approach close enough to inseminate the female without triggering a predatory response. Assuming that the approach signals are exchanged correctly, the male spider must make a timely departure after mating to escape before the female's normal predatory instincts come back into operation.

Male spiders use modified palpi to convey seminal fluid to the genital passages of the female. For a Tidarren male, the palpi constitute 20 % of its body mass. Since this weight greatly impedes its movement, the spider detaches one of the two to gain around 50% increased mobility.

When sexually mature, a male spider will spin a web pad onto which the contents of the abdominal reproductive organs are discharged and then the seminal fluid is transferred into the cavities of the palpi; when an individual secures a mate he thrusts the palpi one at a time into her abdominal genital openings. The seminal fluid is transmitted by a hypodermic-like structure on the male palpus.

Life cycle

Ecology

While spiders are generalist predators, in actuality their different methods of prey capture often limits 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 attempt to bite.

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 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.

Digestion is carried out internally and externally. The spiders secrete digestive fluids into their prey from a series of ducts perforating their jaws, These digestive fluids dissolve the prey's internal tissues.Then, the spider feeds by sucking the partially digested fluids out. Spiders consume only liquid food. Many spiders will store prey temporarily while this process of external digestion is going on. The prey of web weaving spiders that have made a shroud of silk to quiet their struggles while they are dying from envenomation will generally leave the prey in these shrouds and then consume them at their leisure.

Spider webs and prey capture

Some spiders spin funnel-shaped webs, others make irregular webs, and still others make the spiral "orb" webs which are most commonly associated with the order.

The spider, after spinning its web, will then wait (often, but not always, at the center of the web) for a prey animal to become trapped. They 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). Spiders do not usually adhere to their own webs. However, they are not immune to their own glue. Some of the strands of the web are sticky, and others are not. The spiders have to be careful to only climb on the non-sticky strands.

Types of spiders

Tangleweb spiders

• Black widow spider (dangerous)
• Red-back spider (dangerous)
• American house spider (not dangerous)

• St Andrew's Cross spider (also known as an argiope) (not dangerous)
• Long-jawed orb weaver (see above) (not dangerous)
• Cyclosa conica (not dangerous)
• Golden silk spider (see above) (not dangerous)

• Sydney funnel-web spider (dangerous)
• Bowl and doily spiders (not dangerous)
• Hobo spider (dangerous)
• Grass spiders (not dangerous)
• Filmy dome spider (not dangerous)
• Hackled orbweavers (no venom)

• Brazilian Wandering Spider (dangerous)
• Brown recluse spider (dangerous)
• Huntsman spiders (not dangerous)
• Jumping spiders (not dangerous)
• Lynx spiders (not dangerous)
• Nursery web spiders (not dangerous)
• Spitting spiders (not dangerous)
• Tarantulas (not dangerous)
• Wolf spiders (Lycosidae) (not dangerous)
• Yellow sac spider (dangerous)

• Kimura-gumo (Liphistiomorphae) (not dangerous)

Dangerous spiders in the United States include widow spiders, brown recluse spiders, hobo spiders, and yellow sac 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 actually removes one of the biological controls against incursions of the more dangerous species.

If dangerous spiders are present in your area, then be mindful when you move 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.

Black widows

Normally, black widow spider bites are fatal only to children, due to the fact that children have much smaller body weights than adults and so the poison is more concentrated in their bodies when a bite does occur.

There are several widow spiders, i.e., spiders of the genus Latrodectus, and they are generally regarded as all being about equally venomous. Widow spiders are practically blind, and move with difficulty when they are not on their web. Unlike the other problematical spiders, the females of these most toxic of U.S. spiders stay on their web, and the males (which wander around seeking mates) are too small to deliver a dangerous amount of venom.

The website of the Carlsen Ranch asserts that almost half the black widow bites reported in the medical literature from 1901-1941 "were inflicted on the male genitalia by spiders on the underside of outdoor toilet seats." From the standpoint of a spider that likes to make its web under overturned wooden boxes resting on the ground, and in other such sheltered places near the ground, and which eats flies, an outdoor toilet is an almost ideal location. If a black widow happens to be resting near the front edge of the hole when a male human visitor sits down, she may find herself pinned against the wood by his penis, and bite it.

Brown recluse spiders

Brown recluse spiders frequently wander about and so are more easily trapped against one's skin by clothing, bed sheets, etc. The so-called "aggressive house spider" or hobo spider (Tegenaria agrestis) is also a wanderer that may come into contact with people and bite. The yellow sac spiders take shelter in silk tubes during the daytime and come out to hunt at night. People may unintentionally make contact with them in the dark and so be bitten.

Brown recluse spider bites can produce very severe local symptoms, death of tissue around the wound, and, sometimes, severe systemic symptoms. The bites of hobo spiders can cause both pain and necrosis (tissue death), and yellow sac spider bites can be extremely painful.

Huntsman spiders

The huntsman spiders have a worldwide reputation for scaring people. They are large, defend their nests, and may move toward people and make threat displays. They frequently enter houses and hunt over the walls and ceilings where they may run rapidly for long distances without pausing. When they actually do bite people, the bites are very unpleasant, but these spiders are not regarded as dangerous.

There is one spider in California and Japan, prob
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