Spider: Encyclopedia II - Spider - Spider bites

Spider - 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, 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.

Spider - 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.

Spider - Brown recluse spiders and hobo spiders

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.

Spider - 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.

Spider - Redback jumping spiders

Some people have reported being bitten by redback jumping spiders (Phidippus johnsoni). Most reports seem to be from California. These relatively large, alert jumping spiders have bright red abdomens (the females have a black stripe), and should be clearly visible. It is unclear how the bites occur. Accidental contact seems rather unlikely since jumping spiders have excellent vision and could 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. Fortunately, 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.

Spider - 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.

Adapted from the Wikipedia article "Spider bites", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki