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Spider
Orb Weaver Spider at dawn in its web
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Arachnida
Order:
Araneae

Suborders

Mesothelae
Mygalomorphae
Araneomorphae
See Table of Families

Diversity
111 families, 40,000 species

Spiders are predatory invertebrate animals that produce silk, and have two tagma, eight legs, no chewing mouth parts and no wings. Spiders are classified in the order Araneae, one of several orders within the larger class of arachnids, a group which also contains scorpions, whip scorpions, mites, ticks, and Opiliones (harvestmen). The study of spiders is known as arachnology, and those who study spiders are arachnologists.

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 most commonly found on the end of the abdomen. For its weight, spider silk is five times stronger than steel. 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, building egg sacs, wrapping prey, temporarily holding sperm and for many other applications.

All but two families of spiders (Uloboridae and Holarchaeidae) have the ability to inject venom in order to kill and liquefy prey and also to protect themselves. Only a limited subset of spiders can produce significant medical problems by biting humans. Many other of the larger kinds of spiders can give bites that cause discomfort that may continue for some time but will not produce lasting effects.

Morphology

Spider anatomy:
(1) four pairs of legs
(2) cephalothorax
(3) opisthosoma

Spiders, unlike insects, have only two tagmata instead of three: a fused head and thorax (called a cephalothorax or prosoma) and an abdomen (called the opisthosoma). One type of spider which appears to be an exception is the so-called assassin spiders, whose cephalothorax seems to be almost divided into two independent units. Except for a few species of very primitive spiders (family Liphistiidae), the abdomen is not external segmented. 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. This 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).

Spinnerets

The abdomen has no appendages except from one to four (usually three) modified pairs of movable telescoping organs called spinnerets, which produce silk. Originally, the common ancestor of spiders had four pairs of spinnerets, with two pairs on the tenth body segment and two pairs on the eleventh body segment, located in the middle on the ventral side of the abdomen. The suborder Mesothelae, who only has two types of silk glands, is the only place where we can find species with this kind of original anatomy. In all other spiders, which are more advanced, the spinnerets have migrated to the posterior end of the body where they form a small cluster, and the anterior central spinnerets on the tenth segment are lost or reduced (suborder Mygalomorphae) or modified into a specialised and flattened plate called the cribellum (suborder Araneomorphae). The cribellum (usually separated into a left and a right half) produce a thread which is made up of hundreds to thousands of very fine dry silk fibers (about 0.00001 mm thick) around a few thicker core fibers, which then is combed into a wooly structure by using a group of specialized hairs (setae) on their fourth pair of legs. It is suspected their woolly silk is charged with static electricity, causing its fine fibres to attach to trapped prey. Once all araneomorph (modern) spiders had a cribellum, but today it only remains in the cribellate spiders (althought it is sometimes missing even here), which are widespread around the world. Often, this plate lacks the ability to produce silk, and is then called the colulus; an organ which zoologists have not identified a function for. The colulus is reduced or absent in most species. The cribellate spiders were the first spiders to build specialised prey catching webs, later evolving into groups which exclusively using the spinnerets only to make webs, instead using silk threads dotted with droplets of a sticky liquid (like pearls on a necklace) to capture small arthropods, and a few large species even small bats and birds. Other spiders don't build webs at all, but have become active hunters, like the highly successful jumping spiders.

Cephalothorax

Spiders also have eight legs (insects have six), no antennae, and their eyes are single lenses rather than compound eyes. They have pedipalps (or just palps), at the base of which are coxae or maxillae next to their mouth that aid in ingesting food; the ends of the palp are modified in adult males into elaborate and often species-specific structures used for mating. Since they don't have any antennae, they are using specialised and sensitive hairs on their legs to pick up scent, sounds, vibrations and air currents.

Because they can't chew their food, they have, like other Arachnids, a tiny mouth they use as a short drinking straw to suck up the liquid parts of their prey. But they are able to eat their own silk (and some mites are able to eat solid particles as spores).

Respiration and circulation

Spiders have an open circulatory system; i.e., they do not have true blood, or veins to convey it. Rather, their bodies are filled with haemolymph, which is pumped through arteries by a heart into spaces called sinuses surrounding their internal organs.

Spiders have developed several different respiratory anatomies, based either 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 allows 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. This system has most likely evolved in small ancestors to help resist desiccation. The trachae was originally connected to the surroundings through a couple of spiracles, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and migrated posterior close to the spinnerets.

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. Some very small spiders in moist and sheltered habitats don't have any breathing organs at all, as they are breathing directly through their body surface. In the tracheal system oxygen interchange is much more efficient, enabling cursorial hunting (hunting involving extended pursuit) and other advanced characteristics as having a smaller heart and the ability to live in dryer habitats.

Vision

Multiple eyes of jumping spider. Species Platycryptus undatus.

Spiders usually have eight eyes in various arrangements, a fact which is used to aid in taxonomically classifying different species. Species of the series (biology) Haplogynae have six eyes, and there is one family where spiders with no, two or four eyes occur. Sometimes one pair of eyes is better developed than the rest, or there are only three pairs, or even no eyes at all. Several families of hunting spiders, such as wolf spiders and jumping spiders, have developed fair to excellent vision. The main pair of eyes in jumping spiders even sees in colors. However, most spiders that lurk on flowers, webs, and other fixed locations waiting for prey tend to have very poor eyesight; instead they possess an extreme sensitivity to vibrations, which aids in prey capture. Vibration sensitive spiders can sense vibrations from such various mediums as the water surface, the soil or their silk threads. Also changes in the air pressure can be detected in the search for prey.

Life cycle

Spiderlings on a web

The spider life cycle progresses through three stages: the embryonic, the larval, and the nympho-imaginal.[1]

The time between when an egg is fertilized and when the spider begins to take the shape of an adult spider is referred to as the embryonic stage.[1] As the spider enters the larval stage. it begins to look more and more like an adult spider.[1] It enters the larval stage as a prelarva and, through subsequent moults, it reaches its larval form, a spider-looking, non self-sufficient animal feeding off its yolk supply.[1] After a few more moults (also called instars) body structures become differentiated. Soon, all organ systems are complete and the animal begins to hunt on its own; it has reached the nympho-imaginal stage.[1]

The exoskeleton of a spider after moulting

This stage is differentiated into two sub-stages: the nymph, or juvenile stage and the imago, or adult stage.[1] A spider does not become sexually mature until it makes the transition from nymph to imago.[1] Once a spider has reached the imago stage, it will remain there until its death. After sexual maturity is reached, the general rule is that they stop molting, but the female of some non-araneomorphae species will continue to molt the rest of their life.

Many spiders may live only about a year, but a number will live two years or more, overwintering in sheltered areas (the annual influx of 'outdoor' spiders into houses in the fall is due to this search for a nice warm place to spend the winter). It is common for the tarantulas to live around twenty years.

Reproduction

Spiders reproduce by means of eggs, which are packed into silk bundles called egg sacs. Spiders often use elaborate mating rituals (especially in the visually advanced jumping spiders) to allow conspecifics to identify each other and to allow the male to approach close enough to inseminate the female without triggering a predatory response. If the approach signals are exchanged correctly, the male spider must (in most cases) make a timely departure after mating to escape before the female's normal predatory instincts return.

Sperm transmission from male to female occurs indirectly. When a male is ready to mate, he spins a web pad upon which he discharges his seminal fluid. He then dips his pedipalps (also known as palpi), the small, leg-like appendages on the front of his cephalothorax, into the seminal fluid, picking it up by capillary attraction. Mature male spiders have swollen bulbs on the end of their palps for this purpose, and this is a useful way to identify the sex of a spider in the field. With his palps thus charged he goes off in search of a female. Copulation occurs when the male inserts one or both palps into the female's genital opening, known as the epigyne. He transfers his seminal fluid into the female by expanding the sinuses in his palp. Once the sperm is inside her, she stores it in a chamber and only uses it during the egg-laying process, when the eggs comes into contact with the male sperm for the first time and are fertilized; this may be why the vivipary has never evolved in spiders.

Pisaura mirabilis guarding her egg sac, Jerusalem, Israel

Very unusual behaviour is seen in spiders of the genus Tidarren: the male amputates one of his palps before maturation and enters his adult life with one palp only. The palpi constitute 20% of the body mass of males of this species, and since this weight greatly impedes its movement, by detaching one of the two he gains increased 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. [2]

Do female spiders eat their mates?

It is often said that the male (usually significantly smaller than the female, down to 1% of her size as seen in Tidarren sisyphoides) is likely to be killed by the female after the coupling, or sometimes even before intercourse has been initiated. This supposed propensity is what gave the black widow spider, Latrodectus mactans, its name. However, the three species of North American black widows do not seem to usually kill the male (although they have been known to). Males can sometimes even live in the web of a female for a while without being harmed in any way. The male Australian redback spider Latrodectus hasselti is killed ritually by the females after it inserts its second palpus in the female genital opening; in over 60% of cases the female then eats the male. Although the male Latrodectus hasselti may sometimes die during mating without the female actually consuming it, this species represents a possible strategy of "male sacrifice". The male redback, while copulating, 'somersaults' and twists its abdomen directly onto the fangs of its mate. Most males get consumed at this stage (Maydianne CB Andrade reports 65%).[3] Males that 'sacrifice' themselves gain the benefit of increasing their paternity relative to males who do not get cannibalized.[3]

Miturga species in web under rock

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." [4] Michael Roberts says, "It is rare for a fit male to be eaten by the female."[5] 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.[5]

Ecology

Spiders have a great range of variation and lifestyle, although all are predatory.

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. [citation needed]

Predatory techniques

A spider hiding in its leaf (located at the centre of its web)

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 nectar[6]. Several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages in captivity.[6]

Spider webs and prey capture

Main article: Spider web

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.

File:Spider01250.jpg
Having completed its web, a spider in the forests of Malaysia awaits its prey. Appears to be some species of Nephila.

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.

A golden silk orb-weaver (Nephila clavipes?), member of the family Tetragnathidae

Defense

All spiders will attempt to protect themselves by biting, especially if they are unable to flee. Some tarantulas have a second kind of defense, a patch of urticating hairs, or urticating setae, on their abdomens, which is generally absent on modern spiders and Mesothelae. These ultra-fine hairs causes irritation and sometimes even allergic reactions in the attacker. Certain other species have specialized defense tactics. For example, the Golden Wheeling spider (Carparachne aureoflava) of the desert of Namibia escapes tarantula hawks (a species of wasp that lays its eggs in a paralyzed spider so the larvae have enough food when they hatch) by flipping onto its side and cartwheeling away.

Social spiders

A few species of spiders that build webs are living together in large colonies and are showing social behavior, even if it is not as well evolved as in social insects. The most social species are probably Anelosimus eximius, which can form colonies that counts up to fifty thousand individuals.

Evolution

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 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.[7] 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

Main article: Araneae taxonomy

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

Main article: 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

Main article: 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

Main article: 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.

File:Achaearanea tepidariorum (every1blowz).jpg
A tangleweb spider, species Achaearanea tepidariorum

Tangleweb spiders (Theridiidae)

Members of this group are characterized by irregular, messy-looking, tangled, three-dimensional (non-sticky) webs, 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.

Widow spiders
Main article: Widow spider

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

Steatoda
Main article: 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:

Orb web spiders (Araneidae)

An Australian garden orb weaver spider eating a bee

These spiders 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. That being said, some of these spiders can deliver painful bites.

Examples include:

Other forms of webs

Australasian funnel-web spider

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.

Hunting spiders

A Brachypelma smithi

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.

Other spiders

Bird Dropping Spider with its unusual eggs
An Ant Mimic Spider

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

Main article: Spiders having medically significant venom

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:

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

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:

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

Main article: Spiders in popular culture

There are many references to the spider in popular culture, folklore and symbolism. The spider symbolizes patience for its hunting with web traps, and mischief and malice for its poison and the slow death this causes. It symbolises possessiveness for its spinning its prey into a ball and taking it to its burrow (for burrowing species).

See also

References

  1. ^ a b c d e f g Foelix, Rainer F. Biology of Spiders, 2nd edition, 1996.
  2. ^ Journal of Zoology (2001), 254:449–459 Cambridge University Press doi:10.1017/S0952836901000954
  3. ^ a b Andrade, Maydianne C.B. Behavioral Ecology (2003), 14:531–538
  4. ^ Foelix, Rainer F. Biology of Spiders, 1982.
  5. ^ a b Roberts, Michael J. Spiders of Britain and Northern Europe, Collins, London, 1995.
  6. ^ a b Jackson, R.R. et. al. (2001). Jumping spiders (Araneae: Salticidae) that feed on nectar. J. Zool. Lond. 255:25-29 PDF
  7. ^ "LiveScience.com - Oldest Known Spider Web Discovered in Amber". Retrieved June 25. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  • Bristowe, W. S.. The World of Spiders. Collins (New Naturalist), London, 1958.
  • 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.
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