|exerpts from -
A CALL FOR PARSIMONY IN SPIDER BITE DIAGNOSES
by: Richard S. Vetter and P. Kirk Visscher
Department of Entomology, University of California, Riverside, CA 92521 USA
Although some spiders listed in the report can have deleterious effects, not all bites lead to serious symptoms, and most may in fact be unremarkable. Typically, spiders bite only in defense, only once, and the bite is rarely felt. Multiple "bites" or an initially painful bite would exonerate most spiders as probable culprits. There are many arthropods which actively seek to bite humans, and these seem more logical candidates for suspicion 115.
In one study of 600 suspected "spider bite cases" in southern California, 80% were caused by other arthropods, mostly ticks and reduviid bugs 115,116. Loxosceles spiders have been erroneously blamed for a variety of necrotic wounds of unknown origin, which have often turned out to have other etiological agents (Table 1). It has been estimated that 60% of "alleged brown recluse bites" occur in areas where no Loxosceles spiders are known to exist 116. There are many causative agents of necrotic wounds, many not arthropod in nature, which can be or have been confused for recluse spider bites 74,116,118-120. A call for greater parsimony in spider bite diagnoses has been made more than once 74,88,116,117,121 and excellent guidelines for "verified", "probable" and "possible" spider bite diagnoses have been put forth118.
Table 1. Conditions which can cause necrotic
wounds, have been misdiagnosed as or could be confused with "brown recluse
spider bite" (from 73,115-117,120)
Other causes of necrotic wounds are undoubtedly
yet to be discovered. Some may turn out to be due to other spiders. In
the late 1800's, some biologists scoffed at the idea that a tiny black
widow spider could cause death 50,122, it wasn't until 1957 that the brown
recluse spider was proven to be a cause of necrotic lesions in the USA
123, and the hobo spider was implicated in the last 10 years. Even the
extremely poisonous Sydney funnelweb spider was not proven to be dangerous
until 1927 124. These observations argue that
accurate information from physicians can be invaluable in sleuthing out
the causes of now-mysterious lesions, but the search for these causes is
not helped by facile and unsupported diagnoses of "brown recluse bites".