Spider

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

Araneae (spiders)

Long-jawed orb weaver, Family: Aranaedae.
Genus: Tetragnatha. (larger image)

Scientific classification

Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Arachnida
Order:	Araneae

Families

Chelicerae/fang action paraxial -- forward
and downwards =

Suborder: Orthognatha = Mygalomorpha
- - - Families
- Liphisiomorpha
- Mygalomorphae (tarantulas, trapdoor spiders)
  - - Antrodiaetidae (folding trapdoor spiders)
    - Ctenizidae (trapdoor spiders)
    - Theraphosidae (tarantulas)
    - Atypidae (tarantulas)
    - Mecicobothridae

Chelicerae/fang action diaxial - sideways and inwards (pinching).=

Suborder: Labidognatha (= Araneomorpha)
- Entelegynae (most common spiders)
  - Dioncha (jumping and crab)
    - Salticidae (jumping spiders)
    - Thomisidae (crab spiders)
  - Dictynoidea
    - Dictynidae (sievelike spinning plates)
- Lycosoidea (Hunting spiders)
  - - Lycosidae (wolf spiders)
    - Oxyopidae (lynx spiders)
    - Ctenidae (wandering spiders)
    - Pisauridae (nursery web spiders)
- Orbicularia (Orb Weavers, Cob weavers, etc.)
  - - Araneidae (orb weavers)
    - Tetragnathidae (long jawed spiders)
    - Theridiidae (tangle web spiders)
- Haplogynae (recluse, spitting, filistatids, etc.)
  - - Loxoscelidae (brown recluse)
    - Dysderidae (woodlouse hunter)
    - Scytodidae (spitting)
  - Filistatiformia
    - Filistatidae (crevice weavers)

(Temporary location for several families)

- - - Family Linyphiidae (dwarf and sheetweb weavers)
    - Family Sparassidae (giant crab spiders)
    - Family Agelenidae
    - Family Leptonetidae
    - Family Hypochiloidea
    - Family Gnaphosidae
    - Family Sicariidae
    - Family Liphistiidae
    - Family Dipluridae
    - Clubionidae
    - Deinophidae
    - Eresidae
    - Miturgidae
    - Pholeidae
    - Selenopidae
Suborder Cribellatae
Suborder Ecribellatae
Suborder Entelegynae
Suborder Mesothelae
Suborder Neocribellatae
Suborder Opisthothelae

A spider is an invertebrate animal with eight legs belonging to the arachnid order Araneae. This order is further divided into 6 sub-orders. Among them there are the Mygalomorphae (the primitive spiders), the Aranaeomorphae (the modern spiders) and the Mesothelae, which contains the Family Liphistiidae, rarely seen burrowing spiders from Asia.

Many spiders hunt by building webs to trap insects; these webs are made of spider silk extruded from spinnerets on the end of the abdomen, a thin, strong protein strand extruded by the spider. All spiders produce silk, even those which do not spin elaborate traps with them. Silk can be used to aid in climbing, forming smooth walls for burrows, coccooning prey, and for many other applications.

Anatomy

Spiders, unlike insects, have their bodies divided in only two segments: prosoma or cephalothorax (a fused head and thorax) and abdomen. Some species, such as the Tarantula, have urticating hairs all over their bodies. Spiders have 8 legs compared to the insects' 6, and their eyes (usually 8) are single lenses rather than compound eyes like those that insects have. 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 the various kinds of hunting spiders have good to excellent vision, the web weavers and the spiders that lurk on flowers and other fixed locations waiting for some insect to come their way would probably be considered legally blind if they were humans. This is very strange for a predator. How to hunt, if you're almost blind, deaf and you don't smell? The answer lies in their incredible sensitivity to vibrations.

Insects have feelers but spiders don't. Instead, spiders 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 blood does not circulate through vessels, it just fills the body of the spider. This is called an open circulatory system. Book lungs, respiratory organs with openings on the ventral surface of the abdomen, enrich the blood of some spiders with oxygen, and other spiders use spiracles. Some spiders use both.

Reproduction

Spiders reproduce by eggs laid in silk bundles called egg sacs, and the male (usually significantly smaller than the female) is often likely to be killed by the female after the coupling, or sometimes before intercourse has occurred. This propensity is what gave the "black widow" spider (Latrodectus mactans) its name, and there has been much speculation on why it 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 to allow the male to approach close enough to inseminate the female without triggering a predatory response.

Male spiders use modified palpi to convey seminal fluid to the genital passages of the female. When sexually mature, a male spider will spin a web pad onto which the contents of the abdomenal 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.

Ecology

Spiders have a great range of variation and lifestyle, although all are predatory. Spiders are the most important link in the regulation of the number of insects. Every day they devour over 100 kg on 1 hectare of a meadow.

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

Some 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.

Spiders and humans

Most spiders are unlikely to bite humans because they do not identify humans as prey. Spiders, even small spiders, may bite human beings 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. Normally, black widow 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. Unlike the other problematical spiders, the females of these most highly 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. So, "If you don't bother them, they won't bother you."

Widow spiders are practically blind, and move with difficulty when they are not on their web. 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 squeeze them in the dark and so be bitten. The bites of these four spiders may well require medical attention. The widow spiders, brown recluse spiders, hobo spiders, and yellow sac spiders are the dangerous ones among U.S. spiders. None of these spiders will intentionally "come after you," but they should be removed from one's house to avoid accidental injury. Very serious consequences, even death, can follow from widow spider bites. 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 and yellow sac spiders can be extremely painful.

Outside of the U.S., the Brazilian Wandering Spider and the Sydney funnel-web spider frequently bite people and are regarded as among the most dangerous in the world. That being said, none of these spiders move into human territory with the intention of biting people. People blunder into them, and they defend themselves by biting. (There is one spider in California and in Japan, probably a huntsman, that will run over and bite your finger if you touch the wall that it is clambering over, but there is no record of this singularly aggressive and fearless spider causing serious injuries to human beings. Huntsmen females are known as fierce protectors of their young, and will threaten and then attack humans if they do not take the warning. Fortunately, while it is not considered great fun to be bitten by one of these rather large spiders, the bite is painful but not a serious health threat.)

Varieties of spider

Over 37,000 species of spiders have been identified but because of their great ability for hiding it is believed there are near 200,000 species. Almost all species are venomous and only 30 species are deadly dangerous.

Spiders that live on tanglewebs: