Hobo spider: Difference between revisions
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==Toxicity and aggressiveness== |
==Toxicity and aggressiveness== |
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Hobo Spider bites often cause what is referred to by scientists as "The Bruce Banner Effect". This "effect" often causes skin to turn green, unexplained anger and frustration, and in some serious cases, muscle swelling and a dire need to rip buildings to shreds. |
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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.<ref>[http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html]</ref> 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://whatcom.wsu.edu/ag/homehort/pest/hobo.html]</ref> |
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.<ref>[http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html]</ref> 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://whatcom.wsu.edu/ag/homehort/pest/hobo.html]</ref> |
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Revision as of 07:06, 27 October 2009
| Hobo spider | |
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| Hobo spider | |
| Scientific classification | |
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| Species: | T. agrestis
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| Binomial name | |
| Tegenaria agrestis {Walckenaer, 1802}
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| Distribution in North America in green (native European distribution not shown) | |
The hobo spider (Tegenaria agrestis) is a member of the genus of spiders 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.
Toxicity and aggressiveness
Hobo Spider bites often cause what is referred to by scientists as "The Bruce Banner Effect". This "effect" often causes skin to turn green, unexplained anger and frustration, and in some serious cases, muscle swelling and a dire need to rip buildings to shreds.
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.[1] 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.[2]
In the United States, the hobo spider has been considered to be a dangerous species based on a toxicology study on rabbits where lesions appeared after spiders were induced to bite the rabbits,[3] although attempts to replicate the study (by injecting venom to ensure envenomation) have failed to produce necrotic lesions, and there is even question as to whether the lesions observed in the original study were necrotic.[4] This laboratory study has led to the proposal 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.[5] The CDC and other U.S. government agencies (e.g. [3]) have also used this same study as the basis for a report claiming that the hobo spider bite causes necrosis in humans,[6] despite the absence of any confirmed cases. In Canada, there are scientists who claim that no hobo spider bites lead to dermal necrosis.[7] Hobo spiders are common in Europe, though bites are relatively unknown, and there are no confirmed reports of them causing necrosis despite hundreds of years of coexistence there. [citation needed] 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 (phlebitis) that can also cause the appearance of skin lesions.[4]
Hobo spider bites are not known to be fatal to healthy humans. The necrosis in purported cases is similar to, but milder 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.[8][9]
Diagnosis and identification
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 a specimen. Though such experts are not often (if at all) on hospital staff, this step would best determine the course of treatment. It is especially important to remember that if a bite mark was noticed before an encounter with a 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.[10] Spider bite is often confused with other clinical conditions (such as allergic rashes or bites of other insects: mosquitoes, flies, etc.) and it is common but inappropriate to identify skin lesions of unknown origin as "spider bites", as is the case with most reports of hobo spider bites.[11]
Avoiding bites
The best protection against hobo spiders in one's home is probably the presence of other spiders, such as the giant house spider (Tegenaria duellica; formerly Tegenaria gigantea) that will compete with them for territory and food and often kill them in confrontations.[11] 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.[11] Chemical control of spiders is not recommended and should be considered only as a last resort.[12]
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.[11]
Notes
- ^ http://www.washington.edu/burkemuseum/spidermyth/myths/hobo.html
- ^ [1]
- ^ Vest, D. K. (1987). Envenomation by Tegenaria agrestis (Walckenaer) spiders in rabbits. Toxicon 25(2):221-4.
- ^ a b Vetter, R. S. and G. K. Isbister. (2004). Do hobo spider bites cause dermonecrotic injuries? Annals of Emergency Medicine 44:605-607.
- ^ 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.
- ^ [2] Centers for Disease Control and Prevention (CDC). Necrotic arachnidism-Pacific Northwest, 1988-1996. MMWR Morb Mortal Wkly Rep 1996;45:433-6.
- ^ 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.
- ^ Peter Korn (2007-09-21). "Spider bite? Drop the critter in the mail". Portland Tribune. Retrieved 2007-11-02.
- ^ "OHSU Wants Your Spiders, Dead or Alive". Oregon Health & Science University. 2007-09-05. Retrieved 2007-11-02.
- ^ 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
- ^ a b c d Crawford, R. & Vest, D.K. (1988) The Hobo Spider and other European House Spiders. Burke Museum Educational Bulletin No. 1.
- ^ http://www.nature.nps.gov/biology/ipm/manual/ipmmanual.pdf
References
- 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
- Website maintained by the University of California at Riverside with information concerning these spiders
- Website maintained by the family of the author of the rabbit toxicology study
- An example of a necrotic wound blamed on the HS without evidence and a rebuttal from a different newsfeed of the preceding article