Spider

From Free net encyclopedia

(Redirected from Spiders)

Template:Alternateuses {{Taxobox | color = pink | name = Spiders | image = Pisaurina_mira.jpg | image_width = 200px | image_caption = Nursery Web Spider Pisaurina mira
Female with Egg Sac | regnum = Animalia | phylum = Arthropoda | classis = Arachnida | ordo = Araneae | ordo_authority = Clerck, 1757 | subdivision_ranks = Suborders | subdivision = Araneomorphae
Mesothelae
Mygalomorphae
See the taxonomy section for families }}

Spiders are invertebrate animals that produce silk, and have eight legs and no wings. More precisely, a spider is any member of the arachnida order Araneae, an order divided into two sub-orders: the Opisthothelae (which include the infraorders Mygalomorphae (trapdoor and tarantula spiders) and Araneomorphae (the modern spiders)), and the Mesothelae, which contains the Family Liphistiidae, primitive burrowing spiders from Asia. The study of spiders is known as arachnology.

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 as strong as 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 one genus of spiders have the ability to inject venom in order to kill 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.

Contents

[edit]

Morphology and development

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). Except for some few species of very primitive spiders (Liphistiidae), the abdomen has lost its external segmentation. The abdomen and cephalothorax are connected with a thin waist called the pedicle or the pregenital somite. 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). 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.

[edit]

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.

Image:Archindae characters.jpgSpiders have developed several different respiratory anatomies, based either on book lungs, a tracheal system, or both. Some very small spiders probably also directly breathe through their body surface. Primitive mygalomorph 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. Modern araneomorph spiders primarily have an anterior pair of book lungs intact and the posterior pair of breathing organs modified into tracheae, through which oxygen is diffused into the haemolymph. In the tracheal system oxygen interchange is much more efficient, enabling cursorial hunting (hunting involving extended pursuit) and other advanced characteristics.

[edit]

Vision

Spiders usually have eight eyes in various arrangements, a fact which is used to aid in taxonomically classifying different species. Sometimes one pair of eyes is better developed than the rest, or there are only three pairs, or no eyes at all. Several families of hunting spiders, such as wolf spiders and jumping spiders, have developed good to excellent vision. However, most spiders that lurk on flowers, webs and other fixed locations waiting for prey have very poor eyesight, but possess an extreme sensitivity to vibrations, which aids in prey capture.

[edit]

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 on their abdomens, which is generally absent on modern spiders and Mesothelae. Certain other species have specialized defense tactics. For example, the Golden Wheeling spider of the desert escapes Tarantula Wasps (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.

[edit]

Life cycle

Image:Spiderlings.jpg The spider life cycle progresses through three stages: the embryonic, the larval, and the nympho-imaginal (Foelix, 1996).

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 (Foelix, 1996). As the spider enters the larval stage. it begins to look more and more like an adult spider (Foelix, 1996). It enters the larval stage as a prelarva and, through subsequent molts, it reaches its larval form, a spider-looking, non self-sufficient animal feeding off its yolk supply (Foelix, 1996). After a few more molts (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 (Foelix, 1996). This stage is differentiated into two sub-stages: the nymph, or juvenile stage and the imago, or adult stage (Foelix, 1996). A spider does not become sexually mature until it makes the transition from nymph to imago (Foelix, 1996). Once a spider has reached the imago stage, it will remain there until its death. 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.

[edit]

Reproduction

Spiders reproduce by means of eggs, which are packed into silk bundles called egg sacs. Image:Spider egg sac.jpg 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.

Very unusual behavior 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. (Journal of Zoology (2001), 254:449-459 Cambridge University Press Template:DOI)

[edit]

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 for 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 usually to kill the male (although they may) and males can sometimes live in the web of a female for a while without being harmed. The male Australian Redback 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 (known also as the Australian redback spider) 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 (Andrade 2003 reports 65%). Males that 'sacrifice' themselves gain the benefit of increasing their paternity relative to males who do not get cannibalized (see Andrade 2003, Behavioral Ecology vol.14:531-538).

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. Rainer F. Foelix, (1982), says "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.". Michael Roberts (1995) says "It is rare for a fit male to be eaten by the female..." And yet, spider cannibalism does occur in some species more than in others, mainly species belonging to Latrodectus.

There has been speculation on why this sacrifice of male mates might occur despite its obvious disadvantage to the sacrificial males. One theory is that once the male has mated, if he is unlikely to mate again then 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 (1995) that old or unfit males get eaten, whilst younger and fitter ones may survive to mate again.

Another reason promoting male self-sacrifice could be low probabilities of finding another mate. Males of some spider species have a mortality percentage of around 80% (for example L. hasselti from Andrade 2003, and other Latrodectus ssp.). Thus investing more in a mate that has already been found in order to increase paternity resulting from that copulation would increase the probability of transferring the males' genes to the next generation. An accessible discussion of such hypotheses can be found in the entertaining book by Judson (2002).

[edit]

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 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. Template:Citation needed

Image:Spider.jpg

Image:Spider Chiapas Mexico.jpg


[edit]

Predatory techniques

Image:Spider house leaf.jpg

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.

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.

[edit]

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 the order. 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.

Image:Spider01250.jpg

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). 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. For example, if a spider has chosen to wait along the outer edges of its web, it may spin a non-sticky prey or signal line to the web hub to monitor inter-web movement. The spiders have to be careful to only climb on the non-sticky strands.

The ability to spin webs allows a spider to catch prey without having to expend energy by running it down. Thus it is a very efficient method of gathering food. However, constructing the web is in itself an energetically costly process due to the large amount of protein required for the production of the silk. In addition, after a time the silk may lose its stickiness and thus become inefficient at capturing prey, and it may also become torn and tatterd by larger insects that blunder into it and tear their way out again. It is not uncommon for spiders to eat their own web daily in order to recoup some of the energy used in spinning. The silk proteins are thus recycled. The spider, in the middle of the web, also makes for a highly visible prey for birds and other predators. Many day-hunting orb-web spinners reduce this risk; for example, by hiding at the edge of the web with one foot on a signal line from the hub, or by appearing to be inedible or unappetizing. Still other spiders sit fully exposed in the middle of a web but magnify their apparent size by blending their own image with the image of the stabilimentum.

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.

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.

[edit]

Evolution

Trigonotarbids are the oldest known land arthropods. Like spiders, they were terrestrial, respired through book lungs, and walked on eight legs. 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 fimbriungus, 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 patella-­tibia joint of the walking legs.

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 a giant mygalomorph spider and, with its body length of 339 mm and leg span of above 500 mm, the largest known spider ever to have lived on Earth.

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.

[edit]

Types of spiders and the severity of their bites

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 are venomous (with the exception of the families Uloboridae and Heptthelidae), but only 40 species are known to be potentially deadly to humans.

Key to bite severity:

  • Extremely dangerous: Bite (assuming successful envenomation) may cause death in a healthy adults should they not receive emergency medical treatment.
  • Very dangerous: Bite may cause death or debilitatring injury in children, the elderly, and the infirm providing that they do not receive prompt medical treatment.
  • Dangerous: Bite that are unlikely to cause death (generally few or no deaths have been reported); bites may cause significant local or systematic reactions. Medical attention is generally required to limit the scope of symptoms.
  • Painful bites: Venom may inflict localized pain (similar to a bee sting) but does not have any dangerous or long-term side effects. Medical attention is generally not required.
  • Not dangerous: The spider is unable to puncture human skin, and/or its venom does not cause any significant reaction in humans.
  • No venom: Some species do not produce any venom. The only true Family of spiders in this category is the hackled orb-weavers; other Arachnids often confused with spiders, such as the harvestman, also do not produce venom.

A couple of things should be noted when considering the amount of danger posed by spider bites. First, it is often the case that a spider bite is "dry"--the skin may be pierced, but little or no venom is injected into the victim. In such an instance, little or none of the spider's dangerous potential for harm is manifested. Second, there have been reports of spider bites (by spiders considered otherwise harmless) causing allergic reactions in some individuals, up to and including anaphylactic shock, a life-threatening condition (much the same as a sting from an ant, bee, or wasp may produce a harmful effect apart from the toxic quality of its venom). Third, many spiders listed as dangerous are seldom encountered, or have dispositions that make them unlikely to bite despite the high toxicity of their venom. Finally, little is known about the toxicity of many spiders, due to their infrequent encounters with humans; the list of venomous spiders is limited to those that are linked to medical events in humans or who otherwise have been extensively studied.

It should also be noted that, for healthy adults, a bite by even the most toxic spiders on the list may require hours before death ensues; if timely appropriate emergency medical treatment is administered, victims may be expected to recover. The scenario given in movies such as Arachnophobia, where bite victims die within minutes, does not occur. One exception to this picture occurs because in the case of very small children the amount of venom dispersed throughout the body is many times the concentration in an adult. There is at least one recorded case of a small child dying within 15 minutes of a bite from a Sydney funnel-web spider; that event occurred before the development of an antivenin. Since the antivenin was developed there have been no fatalities due to this species.

[edit]

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.

Widows (Latrodectus spp.) - 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 about equally venomous.

Examples:

Steatoda--a large genus which includes the false black widows; these 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:

  • S. grossa (possibly dangerous); bite resembles a very minor widow bite.
  • S. nobilis (painful bites)
  • S. paykulliana (painful bites)

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

[edit]

Orb web spiders (Araneidae)

Image:Garden orb weaver05.jpg These spiders spin the familiar spiral snare that most people think of as the typical spider 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, catching one of these spiders in one's hand is risking a nasty bite.

[edit]

Other forms of webs

Image:Victorian funnelweb.jpg

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.

[edit]

Hunting spiders

Image:Brachypelma edit.jpg

[edit]

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.

[edit]

Other Spiders

Image:Bird dropping spider03.jpg Image:Ant Mimic Spider.jpg

[edit]

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)
  • Daddy-long-legs or harvestman, 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 longlegs" is sometimes used to refer to cellar spiders, which have a similar leg shape; these are true spiders but not dangerous.
[edit]

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.

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 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 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.

[edit]

Black widows

The Black widow spider is one of a number of widow spiders (genus Latrodectus) that carry a neurotoxic venom. Like many spiders, widows have very poor vision (jumping spiders and wolf spiders being notable exceptions), and they move with difficulty when not on their web. Widow spiders are large, strong-looking house spiders (but still have relatively spindly legs and deep, globular abdomens). The abdomen is dark and shiny, and has one or several red spots, either above or below. The spots may take the form of an hourglass, or two triangles, point-to-point. Male widows, like most spiders, are much smaller than the females, and may have a variety of streaks and spots on a browner, less globular abdomen. The males are generally considered to be much less dangerous (if at all) than the females. Widows tend to be quite non-aggressive, but will bite if the web is disturbed and the spider feels threatened. The venom, although rarely life-threatening, produces very painful effects including muscle spasms and 'tetanus-like' contractions. A serious bite will often require a short hospital stay. Children, elderly, and ill individuals are at most risk of serious effects.

[edit]

Brown recluse spiders and hobo spiders

Image:Brown recluse.jpg Brown recluse spiders, (or "Violin Spiders" from the dark violin-shaped marking on the cephalothorax) Loxosceles reclusa, are slow-moving, retiring spiders which wander about in dim areas and under things, and so are more easily trapped against one's skin by clothing, bed sheets, etc. Even so, most encounters with this spider occur from moving boxes or rooting about in closets or under beds. The range of this spider in the US is approximately the lower 2/3 of the country by the eastern 3/4 of the country. A number of related Recluse spiders (some non-native introductions) are found in southern California and nearby areas, as well. The hobo spider, Tegenaria agrestis, may wander away from its web, especially in the fall, and thus come into contact with people and bite. This spider is found in the northwestern United States and throughout much of Europe. Oddly enough, in Europe it is considered a harmless outdoor relative of the common House Spider (Tegenaria domestica). The yellow sac spiders, Chiracanthum sp., take shelter in silk tubes during the daytime and generally come out to hunt at night. These pale yellow or whitish spiders are often found in houses at the top of walls, or wandering across ceilings. They are also commonly found outdoors on foliage. The draglines they leave while hunting are one of the most common "cob-webs" that are removed with broom and vacuum cleaner. People may unintentionally make contact with them in the dark and so be bitten. However, most people will live their entire lives in close proximity to them and never suffer a bite.

Brown recluse spider bites can produce very severe local symptoms, death of tissue around the wound, and, sometimes, severe systemic symptoms, including organ damage. The bites of hobo spiders and yellow sac spiders can cause both pain and necrosis (tissue death). Typically, all these bites are characterized by open, sore-like wounds that heal very slowly and may leave scarring. It has been suggested that steroid treatments may speed healing and reduce scarring.

It is believed that many spider bites which are attributed (often by physicians and other medical personnel) to the brown recluse are in fact caused by the hobo spider (if caused by a spider at all). Many brown recluse bites are reported in the U.S. west coast states (Washington, Oregon, and northern California) where populations of brown recluse spiders have not been found.

There are other species of spider in the genus Loxosceles which are found in southern California and other southwestern states; most of these species live in remote areas and are rarely encountered by humans. Bites of Loxosceles spiders found in South America are more serious in their consequences than their North American relatives.

[edit]

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. They are quite common in parts of Australia. Australian huntsman spiders are typically non-aggressive except when defending their nests or their young.

There is one spider in California and Japan, probably a huntsman (tentatively identified as a member of the Sparassidae family, Heteropoda venatoria), which might run over and bite your finger if you touch the wall that it is clambering over. That behavior may well occur because its eyesight is good enough to see movement and general shape, but not sufficient to avoid mistaking something else for its natural prey. In general, however, members of this genus scramble wildly to escape when they become aware of a human moving into their vicinity.

[edit]

Redback jumping spiders

Some people have reported being bitten by redback jumping spiders (Phidippus johnsoni). Many reports come from California,although their range is much wider and people elsewhere may have unpleasant contacts with them. These relatively large, alert but slow-moving jumping spiders have bright red abdomens (the females have a black stripe), and should be clearly visible. It is unclear how bites to humans occur. Accidental contact seems rather unlikely since jumping spiders have excellent vision and can easily avoid being brushed by a human hand. It is also unlikely that they would mistake a human finger for their natural prey. One source suggests that, since they are quite attractive, children may try to pick them up and in that way elicit a defensive bite. Since these spiders are quite large, their body length being around 12 mm (1/2 inch), the volume of their available venom is accordingly rather large. Fortunately, however, the worst consequences reported have been three to four days of discomfort, with no permanent damage. Like most of the larger spiders, the consequences of a bite seem little different than a wasp or bee sting. Since they do not frequent human habitations it should ordinarily be easy to avoid unpleasant contact with them.

Female Phidippus johnsani (?) 12.5 mm.

Large, slow moving, and attractive, some are bright red and may tempt children.

These spiders will give defensive bites.

[edit]

Brazilian wandering spiders and Australian venomous funnel-web spiders

The Brazilian wandering spider (a ctenid spider) and the Australian venomous spiders such as the Sydney funnel-web spider (a mygalomorph only distantly related to the araneomorph funnel-web spiders) frequently bite people and are regarded as among the most dangerous in the world. They are quite aggressive spiders, and are prone to biting when confronted, rather than running away. The Sydney funnel-web spider, a large, bulky, black spider, is restricted to a relatively small area around Sydney, Australia. It is unequivocally the most venomous spider in the world; although Phoneutria has the most neurologically active venom, it is delivered in amounts rarely large enough to cause deaths. There are other dangerous species of Atrax and Hadronyche related to this spider in surrounding parts of Australia, including Tasmania. The males in this case have somewhat more potent venom than females and they also wander, making them more likely to be encountered in summer. The Brazilian wandering spider is a large, brown spider rather like a North American Wolf spider in appearance. It, like several other more harmless spiders, may hitch a ride in clusters of bananas. As a result, any large spider appearing in a bunch of bananas should be treated with due care. Oddly, many of the bites of this species are dry bites and no venom is released. The spiders are as large as some small tarantulas and have fairly long fangs. While venom from either spider can be deadly to children and the infirm, since the development of antivenom to the venoms of both were developed (the funnel web spider in the mid-1980's and the wandering spider in 1996), no humans have died from their bites. Nevertheless, any large spider which makes a threat display (raising front legs, rearing back to display fangs) when encountered should be treated with caution - especially in areas where these two types of spiders may be expected.

Brazilian Wandering Spider

Atrax robustus
Sydney Funnel-web Spider

Range of the two genera (Hadronyche and Atrax) of venomous Australian funnel-web spiders.

[edit]

Taxonomy

For an extensive list of the genera and species of the most common kinds of spiders world-wide, see Araneae taxonomy.

[edit]

Symbolism

The spider symbolizes patience, for its hunting with web traps. Some fictional and mythological characters are related to spiders:

The Italian dance and music tarantella is related to tarantulas, either as a folk remedy for bites or from its vigorous movements.

[edit]

Spiders in films and popular culture

  • Spider-Man-a Marvel Comics character/Superhero created by writer Stan Lee and artist Steve Ditko.
  • Arachnophobia (film)-a movie directed by Frank Marshall, in which spiders multiply in large numbers and kill humans.
    • Arachnophobia (video game)-a video game based on the film Arachnophobia, developed by BlueSky Software and Disney for the DOS and Commodore 64 platforms.
  • Spider!-a 1998 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-a 2002 film in which spiders get mutated because of harmful nuclear waste in mines and hence become oversized creatures and hunt humans.
  • Harry Potter and the Chamber of Secrets-Hagrid's pet creature is a giant spider, which then runs away to live in the forest.
  • Kingdom of the Spiders - This stars William Shatner as a veteranarian who has to deal with spiders after the spiders' food sources were destroyed by heavy use of insecticides. The film was made by Dimension Pictures, lasts 95 min., is on DVD. At the end of the movie, the spiders kill and eat all of the people in Arizona. It is in color.
  • Spinarak
  • Ariados
  • Shelob, a giant spider-like creature in the Lord of the Rings saga.
  • In Jumanji (film), one of the group of creatures which appears is a group of giant spiders.
[edit]

See also

[edit]

References

  • The World of Spiders, by W. S. Bristowe Collins (New Naturalist), London 1958
  • The Life of the Spider, by John Crompton. Mentor, 1950.
  • Biology of Spiders, by Rainer F. Foelix, 1982 and second edition, 1996
  • The Book of the Spider, by Paul Hillyard, Random House, New York 1994
  • Dr. Tatiana's Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex, by Olivia Judson, Metropolitan Books 2002
  • How to Know the Spiders, by B. J. Kaston. Dubuque, 1953
  • Spiders, by Barbara York Main, Collins (The Australian Naturalist Library), Sydney 1976
  • Spiders of Britain and Northern Europe, by Michael J. Roberts, Collins, London 1995
  • Spiders of North America: an Identification Manual, by Darrell Ubick, Pierre Paquin, Paula E. Cushing, and Vincent Roth, American Arachnological Society 2005

Wise, David H. "Spiders in Ecological Webs." Cambridge University Press. Great Britain: 1993.

[edit]

External links

Template:Commons

Template:Link FA Template:Link FA

als:Webspinne ar:عنكبوت bg:Паяци zh-min-nan:Ti-tu ca:Aranya cy:Corryn da:Edderkopper de:Webspinnen es:Araneae eo:Araneo fr:Araneae gl:Araña ko:거미 io:Araneo is:Könguló he:עכבישאים lt:Vorai nah:Tócatl nl:Spinnen (dieren) ja:クモ no:Edderkopper pl:Pająki pt:Aranha scn:Taràntula (Araneae) sl:Pajek fi:Hämähäkit sv:Spindlar tr:örümcekler uk:Павук zh:蜘蛛

Retrieved from "http://www.netipedia.com/index.php/Spider"