The recluse spiders, genus Loxosceles, belong to a unique family of arachnids known as the Sicariidae, or six-eyed sicariid spiders. The sicariids have six (rather than the typical eight) eyes, arranged in a horseshoe pattern in three clusters of two eyes each. The family consists not only of the recluse spiders, but also of the six-eyed crab spiders, genus Sicarius, of Central and South America, and South Africa. Recluse spiders were the first spider group to be recognized as a causative agent of the disease state now known as necrotic arachnidism, and this condition, when caused by a recluse spider, is properly termed loxoscelism. Loxoscelism was first recognized in 1872 when Chilean physicians linked a peculiar skin lesion known as the "gangrenous spot of Chile" to bites by the Chilean recluse spider, Loxosceles laeta. The brown recluse, L. reclusa, became the first U.S. spider associated with necrotic arachnidism in 1957, when it was linked to severe bites in the midwest. All recluse spiders, as well as the six-eyed crab spiders, are now considered venomous to humans.
At least 56 species of recluse spiders have been described, 54 from the Americas, one from the Mediterranean region, and one from South Africa: Many of these species have only recently been recognized, and thus, most people are not familiar with them. In natural habitats recluse spiders live beneath rocks and fallen debris: In areas inhabited by humans, they take up residence inside houses and other buildings, and may be found in attics, barns, cellars and storm shelters; They can often be found hiding in the folds of clothing, shoes, or underneath boxes in storage rooms. Most species have a mild temperment, and bite only when accidentally pressed against skin, but others, such as the Chilean recluse, are less even tempered.
In the United States there are eleven indigenous (native) species of recluse spider, and two species introduced from other countries. The most noted of these is the brown recluse spider, Loxosceles reclusa (photograph), the latin name of which translates "slant-legged recluse". The brown recluse is found in the midwest and parts of the south; it ranges (see map ) from southern Wisconsin east to Ohio, and south to extreme northern Florida and central Texas. The adult brown recluse has a body length of 10-12 mm. This species is also frequently called the "fiddleback" or "violin" spider, due the violin-like marking on the dorsal cephalothorax. The apparent presence of a violin-like marking on the cephalothorax or elsewhere is not sufficient to identify a spider as belonging to the recluse group. Many other spiders have markings which somewhat resemble "violins".
The other ten recluse species which are indigenous to the United States look very much like reclusa and can be positively distinguished only by an expert. Other U.S. indigenous and introduced recluse spiders are:
Recluse spider bites can produce the same type of local effects as those described for the hobo spider in Hobo Spider Poisoning, with the development of a slow healing necrotic lesion. The systemic effects of brown recluse spider bite (which occur in a small percentage of cases) differ somewhat from those of the hobo; chills, fever, nausea, muscle pain, and other flu-like symptoms can develop. In severe cases convulsions may occur, as well as abnormalites in the clotting ability of the blood. Hemolysis, or damage to red blood cell walls resulting in leakage of the red, oxygen carrying protein hemoglobin occurs in some cases; this can result in the death of the victim when the discarded red blood cell casts are filtered through the kidneys, causing renal failure. Bites by the recluse spiders should (for the moment) be treated in the same fashion as has been outlined for the hobo spider. Management of the local lesion, and the use of corticosteroids in systemic poisoning, are the key elements in treatment of bites by recluse spiders. Systemic poisoning from the various members of the genus Loxosceles may vary from species to species. Little is known about the venom and bite of the lesser known species of recluse spiders.
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