Arachnid Science: Article Reviews
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Vetter, R.S., G.B. Edwards, & L.F. James. 2004. Reports of envenomation by brown recluse spiders (Araneae: Sicariidae) outnumber verification of Loxosceles spiders in Florida. Journal of Medical Entomology 41: 593-597.
Talk about getting a bad rap! This article compiles facts from a number of sources that, when taken together, clearly lead to the conclusion that the number of envenomations attributed to Loxosceles reclusa (the brown recluse spider) in the state of Florida (USA) are dramatically overdiagnosed by medical personnel.
First, the authors established how prolific is the population of Loxosceles spiders in the state by studying the frequency and distribution of positively confirmed specimens for the last century. Since 1904, approximately 70 Loxosceles spiders have been found in 10 of the 67 counties in the state (dates and exact locations of these spiders provided). Over half of these spiders were from an infestation within a single home. Obviously, the Florida Loxosceles population is not abundant or widely distributed.
Three poison centers, all part of the Florida Poison Information Center Network, contributed data on the 844 calls they received during a six-year period (1997-2002) from individuals claiming to have been bitten by a brown recluse. The focus of this article is on the subset of 124 of those reports for which it was later confirmed that brown recluse envenomation was diagnosed by a medical professional. These 124 cases, most or all of which were likely misdiagnoses, occurred in 31 counties, only 6 of which have ever yielded a confirmed brown recluse spider in the last 100 years.
One of the authors, G.B. Edwards, has served as the arachnid curator of the Florida State Collection of Arthropods for 25 years and has inspected hundreds of submitted spiders that were purportedly brown recluses. According to Edwards, there has only been a single case in which someone claiming to have received a brown recluse bite presented the correct species for verification.
An extensive nationwide research project is ongoing to survey Loxosceles populations throughout the United States. The number of alleged brown recluse spiders submitted for identification in Florida were compared to submissions in four other states endemic to Loxosceles: Texas, Missouri, Kansas, and Oklahoma. None of the alleged brown recluses in the Florida sample were confirmed as such; instead, most were wolf, huntsman, or crevice spiders. In contrast, the majority (64%-88%) of the suspected recluses submitted in the comparison states were positively identified. That this species does not pose a critical threat to humans is underscored by the fact that many brown recluses are captured in homes and other buildings in these states without the occupants receiving bites.
The true source of many of the misdiagnosed necrotic skin symptoms mistakenly attributed to Loxosceles is difficult to ascertain. In many cases misdiagnosed skin lesions are actually not a spider bite of any sort! The actual cause of the lesion may be melanoma or microbe infection, or the lesion may be secondary to autoimmune disorders, hypertension, or diabetes.
The number of recluse bites diagnosed in Florida and these 124 cases in the present paper are but a fraction—is virtually impossible given the distribution of Loxosceles spiders within the state. Unfortunately, the tendency to mistakenly blame skin lesions on these spiders is not unique to Florida. For example, Vetter published a study in 2003 with other colleagues that showed similar patterns of overestimating brown recluse envenomations in Washington, Oregon, California, and Colorado. Loxosceles spiders are perceived to be more widespread and dangerous to humans than they really are. Beyond affecting the misdiagnosed patient, who may not get the prompt or appropriate treatment for the skin lesion, this tendency for the medical profession to overestimate the frequency of recluse bites affects public perception and encourages fearful or even extreme phobic reactions to brown recluses and other spiders.
This journal is published by the Entomological Society of America [http://www.entsoc.org].