article

The brown recluse spider is a venomous spider, Loxosceles reclusa, of the family Sicariidae (formerly of the family Loxoscelidae). It is usually between 1/4 and 3/4 inch (6.4-19.1mm) but may grow larger. It is brown and usually has markings on the dorsal side of its thorax, with a black line coming from it that looks like a violin with the neck of the violin pointing to the rear of the spider resulting in the nickname "fiddleback spider" or "violin spider". Coloring varies from light tan to brown and the violin marking may not be visible. Since the "violin pattern" is not diagnostic, it is far more important, for purposes of identification, to examine the eyes. Contrary to most spiders, which have 8 eyes, recluse spiders have 6 eyes arranged in pairs (dyads) with one median pair and 2 lateral pairs. Only a few other spiders have 3 pairs of eyes arranged this way (e.g., scytodids), and recluses can be distinguished from these as recluse abdomens have no coloration pattern nor do their legs, which also lack spines.

The brown recluse spider is native to the United States from the southern Midwest south to the Gulf of Mexico (*). The native range lies roughly south of a line from southeastern Nebraska through southern Iowa, Illinois, and Indiana to southwestern Ohio. In the southern states, it is native from central Texas to western Georgia. They are generally not found west of the Rocky Mountains.

Recluse spiders, which also include Mediterranean recluse spider (Loxosceles rufescens), build irregular webs that frequently include a shelter consisting of disorderly threads. Unlike most web weavers, they leave these webs at night to hunt. People get bitten when they unintentionally squeeze them in clothing and bedding.

These spiders frequently build their webs in woodpiles and sheds, closets, garages, and other places that are dry and generally undisturbed.

A venomous bite

As indicated by its name, this spider is not aggressive and usually bites only when pressed against human skin, such as when putting on an article of clothing. Actual brown recluse bites are rare and few. The initial bite frequently cannot be felt. Most bites are minor with no necrosis, but a small number produce severe dermonecrotic lesions or even systemic conditions (viscerocutaneous loxoscelism) with occasional fatalities. (For a comparison of the toxicity of several kinds of spider bites, see the list of spiders having medically significant venom.)

The serious bites form a necrotising ulcer that destroys soft tissue and may take months and very rarely years to heal, leaving deep scars. The damaged tissue will become gangrenous and eventually slough away. Initially there may be no pain from a bite, but over time the wound may grow to as large as 10 inches (25 cm) in extreme cases. Bites may take up to seven hours to cause visible damage; more serious systemic effects may occur before this time, as venom of any kind spreads throughout the body in minutes. Deaths (1.5% of all cases) have been reported for the related South American species L. laeta and L. intermedia.

First aid involves the application of an ice pack to control inflammation, the application of aloe vera to soothe and help control the pain, and prompt medical care. If it can be easily captured, the spider should be brought with the patient in a clear, tightly closed container so it may be identified. However, by the time the bite is noticed any spider found nearby is not likely to be the culprit.

Misdiagnoses

It is estimated that 80% of reported brown recluse bites may be misdiagnoses. The misdiagnosis of a wound as a brown recluse bite could delay proper treatment of serious diseases (*). There is now a test for brown recluse venom that can determine if a wound is a brown recluse bite.

There are some 30 documented conditions (including pyoderma gangrenosum or bacterial infections by Staphylococcus and Streptococcus) that produce wounds that have been initially misdiagnosed as recluse bites by medical professionals (*); many of these conditions are far more common and more likely to be the source of mysterious necrotic wounds, even in areas where recluses actually occur. Therefore, the existence of a necrotic wound does not automatically indicate that a spider bite was the cause.

Reported cases of bites occur primarily in Texas, Kansas, Missouri, and Oklahoma. There have been many reports of brown recluse bites in California (and elsewhere outside the range of the brown recluse); however the brown recluse is not found in California (*) (though a few related species may be found there, none of which have been shown to bite humans). Many arachnologists believe that many bites attributed to the brown recluse in the West Coast are not spider bites at all, or possibly instead the bites of other spider species (such as the hobo spider, which has been reported to produce similar symptoms, and is found in the northwestern United States and southern British Columbia in Canada).

Lookalikes

Often, a spider of a different species may be mistaken for a brown recluse spider. Misidentification of spiders as brown recluses is not uncommon even in the medical community, as few doctors receive formal training in spider identification; as noted above, the only reliable diagnostic is the structure of the eyes, which typically requires the use of a stereo microscope. Many mistaken spiders are generally harmless, and only share the characteristics of brown color and eight legs, or a pattern on the cephalothorax.

Spiders commonly mistaken for brown recluses:

External links

Sicariidae | Dangerous spiders

Loxosceles reclusa

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Brown recluse spider".

Home Page • arts • business • computers • games • health • hospitals • home • kids & teens • news • physicians • recreation• reference • regional • science • shopping • society • sports • world