Hobo spider
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2008-07-06T13:50:31Z
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/* Toxicity and aggressiveness */ Removed incorrect use of apostrophe
{{Taxobox
| name = Hobo spider
| image = female-hobo.gif
| image_width = 250px
| image_caption = Hobo spider
| regnum = [[Animal]]ia
| phylum = [[Arthropod]]a
| classis = [[Arachnid]]a
| ordo = [[Spider|Araneae]]
| familia = [[Agelenidae]]
| genus = ''[[Tegenaria]]''
| species = '''''T. agrestis'''''
| binomial = ''Tegenaria agrestis''
| binomial_authority = {[[Charles Athanase Walckenaer|Walckenaer]], 1802}
| range_map = Tegenaria agrestis distribution.PNG
| range_map_width = 250px
}}
The '''hobo spider''' (''Tegenaria agrestis'') is a member of the genus of [[spider]]s known colloquially as funnel web spiders. It is one of a small number of spiders in North America whose bites are generally considered to be medically significant. Individuals construct a [[funnel]]-shaped structure of silk sheeting and lie in wait at the small end of the funnel for prey insects to blunder onto their webs. Hobo spiders sometimes build their webs in or around human habitations. Although this species of spider has a reputation for aggressiveness, they will normally avoid contact with humans. Most bites occur when the spider is accidentally crushed or squeezed by a human. The spider's venom is strong enough to cause considerable local pain and there are unconfirmed reports that it may cause tissue death ([[necrosis]]) at and near the bite.
==Appearance==
The female reaches sizes of 11–15 mm (.43–.6 in); the male 8–11 mm (.31–.43 in). There is no [[Sexual dimorphism|dimorphism]] in colour or markings. Their coloration is rather subdued, being a mixture of brown and rust earth shades. They have a herringbone pattern on the top side of their abdomens. Although most [[Agelenidae]] have very "hairy"-looking legs, the legs of this spider are fairly smooth. Lookalikes have stripes on the legs and are often much larger—the hobo spider has solid light-brown-colored legs. Related species are quite similar in appearance, and it requires technical training to identify them reliably.
The web is a flat or curved sheet of dense silk, curved upwards at the edges, and slanting down to one corner where it forms a funnel-like tubular retreat; the spider rests there, and has an escape hole at the back. The web captures prey that fall on it from above, and insects that fall into it become tangled in the irregular "trip threads" over its surface; the hobo's web is not sticky. Prey includes household pests such as [[cockroach|roach]]es, [[houseflies]], [[earwig]]s, [[silverfish]], and [[carpet beetle]]s.<ref name="Crawford">Crawford, R. & Vest, D.K. (1988) The Hobo Spider and other European House Spiders. Burke Museum Educational Bulletin No. 1.</ref>
==Habitat and distribution==
''T. agrestis'' is indigenous to western and central [[Europe]], but is now also found in the northwestern [[USA]] and southwestern [[Canada]]. It has recently spread to [[Southeast Alaska|southern Alaska]], becoming the first spider considered dangerous to humans in the state.<ref>http://www.webmd.com/hw/health_guide_atoz/tm6500.asp Symptoms</ref> Recently it has been found in great numbers in [[Denmark]] on a small island ([[Peberholm]]), which is on the route of the [[Oresund Bridge|Oresund highway]], and according to media it has spread from there to the province of [[Skåne]] in southern [[Sweden]], though there have not been any reported bite cases.
It prefers moderately dry and warm environments, but in Europe does not typically live in houses, largely due to competition from house spiders such as ''[[Tegenaria duellica]]'', which also occurs in the Pacific Northwest.<ref name = Crawford/> It is most commonly found in [[garden]]s, fields, hedges, and the like. It is quite rarely found in houses in Europe, where almost no envenomations have been reported, and the harmless if similar-looking ''[[Tegenaria domestica|T. domestica]]'' and ''[[Tegenaria saeva|T. saeva]]'' are far more common.
As a rule, and especially in the mild climate west of the [[Cascade Mountains|Cascades]], hobo spiders are perceived primarily as a problem in August or September, when the short-lived males are active.<ref name = Crawford/>
==Toxicity and aggressiveness==
The toxicity and aggression of the hobo spider are currently disputed by scientists. Its nickname "aggressive house spider" comes from a misinterpretation of the [[Latin]] name ''Agrestis'', which literally translates to "of the fields", but is mistranslated as "aggressive". If a hobo spider is tending an egg sac, it may become aggressive if it perceives the egg sac to be threatened. However, they generally do not bite unless forced to protect themselves, and in the majority of cases the hobo spider does not actually inject venom when it does bite<ref>[http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html]</ref>.
In the United States, the hobo spider has been considered to be a dangerous species based on a toxicology study on [[rabbit]]s where injected venom produced [[necrosis|necrotic]] [[lesion]]s <ref>Vest, D. K. (1987). Envenomation by ''Tegenaria agrestis'' (Walckenaer) spiders in rabbits. ''Toxicon'' 25(2):221-4.</ref>, although attempts to replicate the study have failed to produce necrotic lesions. Due to this one study, it has been proposed that in some parts of the U.S. nearly all bites imputed to the [[brown recluse spider]] are in reality the hobo spider's bite <ref>Vest, D. K. (1987). Necrotic arachnidism in the northwest United States and its probable relationship to ''Tegenaria agrestis'' (Walckenaer) spiders. ''Toxicon'' 25(2):175-84.</ref>. The [[Centers for Disease Control and Prevention|CDC]] used this same study again as the basis for a report claiming that the hobo spider bite causes necrosis in humans, despite the absence of any confirmed cases<ref>Centers for Disease Control and Prevention (CDC). Necrotic arachnidism-Pacific Northwest, 1988-1996. MMWR Morb Mortal Wkly Rep 1996;45:433-6.</ref>. In Canada, there are scientists who claim that no hobo spider bites lead to dermal necrosis<ref>Bennett, R. G. and R. S. Vetter. (2004). An approach to spider bites: erroneous attribution of dermonecrotic lesions to brown recluse and hobo spider bites in Canada. ''Canadian Fam. Physician'' 50: 1098-1101.</ref>. Hobo spiders are common in Europe, though bites are relatively unknown, and do not cause necrosis<ref>[http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html]</ref>. Nonetheless, it is believed by some that hobo spiders are dangerous to humans. The only documented case of a verified hobo spider bite leading to necrotic skin lesions involves a person who had a pre-existing medical condition that also leads to necrotic skin lesions<ref>Vetter, R. S. and G. K. Isbister. (2004). Do hobo spider bites cause dermonecrotic injuries? ''Annals of Emergency Medicine'' 44:605-607.</ref>.
Hobo spider bites are not known to be fatal to healthy humans. The necrosis in purported cases is similar to, but more mild than, that caused by the brown recluse spider, and in severe cases can take months to heal. Other reported symptoms include intense headaches, vision abnormalities, and/or general feelings of [[malaise]]. These symptoms are not confirmed for the hobo spider bite specifically due to lack of positive identification of the spider by an expert, and the [[Oregon Poison Center]] (affiliated with the [[Oregon Health & Science University]]) is attempting to gather definitive evidence regarding the validity of these reports as of September 2007<ref>{{cite news|url=http://www.portlandtribune.com/news/story.php?story_id=119032341162984200|
title=Spider bite? Drop the critter in the mail|work=[[Portland Tribune]]|date=2007-09-21|
author=Peter Korn|accessdate=2007-11-02}}</ref><ref>{{cite web|url=http://www.ohsu.edu/ohsuedu/newspub/releases/090507spider.cfm|title=OHSU Wants Your Spiders, Dead or Alive|date=2007-09-05|publisher=[[Oregon Health & Science University]]|accessdate=2007-11-02}}</ref>.
== Bite treatment ==
{{POV-section|date=December 2007}}
{{main|Spider bite}}
In case of being bitten by a Hobo spider, it is best to capture it immediately. One way of doing this is by dropping a drinking glass over the spider, sliding a card or a sheet of stiff paper under the glass, then flipping it over and securing the top. It is especially important to remember that if a bite mark was noticed before an encounter with this spider, this is not evidence that the spider was responsible; this is the most common source of false reports, which - most significantly - have often led to misdiagnosis and mistreatment, with potentially life-threatening consequences.<ref>Vetter, R. S. (2000). Myth: Idiopathic wounds are often due to brown recluse or other spider bites throughout the United States. ''[[Western Journal of Medicine]]'' 173:357-358</ref> Spider bite is often confused with other clinical conditions, and it is common but inappropriate to identify skin lesions of unknown origin as "spider bites".<ref name = Crawford/> If, after a known bite, major discomfort is experienced and medical assistance is required, then a spider expert may be needed to confirm the identity of the spider. Though such experts are not often (if at all) on hospital staff, this step would best determine the course of treatment.
Treatments for more minor bites should be as for any puncture wound. The wound should first be encouraged to bleed to wash out any foreign material and debris. (Many wounds will not bleed because they are so small in diameter that they seal immediately.) Then a topical antiseptic such as buffered iodine (a typical brand name product would be [[Isodine]]) should be applied on the off chance that the bite introduced a virus or microbe beneath the skin level and that the antiseptic will penetrate to that depth. Spider bites should never be scratched, and should be observed for a couple of days so that medical attention can be sought if signs of infection appear.<ref name = Crawford/><ref>Wilkerson, James A., M.D. (1967). ''Medicine for Mountaineering'', Seattle. p. 50</ref> Never take [[aspirin]] or use heat packs or cold packs in cases of hobo envenomation, as these may increase or intensify tissue damage or even cause [[hemorrhage]].<ref name = Crawford/>
==Avoiding bites==
The best protection against hobo spiders in one's home is probably the presence of other spiders, such as ''Tegenaria duellica'' (formerly ''Tegenaria gigantea'') that will compete with them for territory and food and often kill them in confrontations.<ref name = Crawford/> Killing all spiders by using insecticides can result in the proliferation of a single species when its competition disappears, and since spiders consume many household pest insects, eliminating spiders can have serious consequences.<ref name = Crawford/> Chemical control of spiders is not recommended and should be considered only as a last resort.[http://www.nature.nps.gov/biology/ipm/manual/ipmmanual.pdf]
Normal care should be exercised when disturbing webs or moving long-unused boxes. Spiders do not perceive humans as prey, and the only reason they have for biting is self-defense. If it becomes necessary to remove a spider's funnel web, it is prudent to do so by gently sweeping it away with a broom. If a spider is in or on a box, it will usually leave as quickly as possible when the box is disturbed.<ref name = Crawford/>[http://www.cepis.ops-oms.org/bvsapud/i/fulltext/spiders/spiders.pdf]
==Notes==
<references/>
==References==
* [http://www.lclark.edu/~biology/Binford/Toxicon2001.pdf Binford, J. G. (2001). "An analysis of geographic and intersexual chemical variation in venoms of the spider ''Tegenaria agrestis'' (Agelenidae). ''Toxicon'' 39:955-968]
* Bolzern, A. & Hänggi, A. (2006). Phylogeny of ''Tegenaria'' (Araneae, Agelenidae), with special focus on the human-biting ''Tegenaria agrestis''-complex: a revision using morphological and molecular data.
==External links==
{{commons|Tegenaria agrestis}}
* [http://spiders.ucr.edu/dermatol.html Website maintained by the University of California at Riverside with information concerning these spiders]
* [http://hobospider.org/ Website maintained by the family of the (now-deceased) author of the rabbit toxicology study]
* [http://www.msnbc.msn.com/id/16160932/ An example of a necrotic wound blamed on the HS without evidence] and [http://seattlepi.nwsource.com/local/295595_hobos12.html a rebuttal from a different newsfeed of the preceding article]
{{Araneae}}
[[Category:Tegenaria]]
[[Category:Spiders of North America]]
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