Recluse spiders--also known as violin spiders or fiddleback spiders, owing to the distinctive violin-shaped marking on their backs just behind the eyes--are one of the few species of spiders known to cause medically significant bites. While all recluse spider bites are painful, sometimes exceedingly so, most will resolve on their own within about a week. In a minority of cases, more severe complications can occur, up to and including coma and death, though this is extremely rare.
Recluse spiders belong to the genus Loxosceles, and are endemic to North and South America. In the U.S., they are found in widespread regions of the South, Midwest and Southwest. In South America, where they are known simply as brown spiders, they can be found mostly in Chile and Brazil. As their name suggests, they prefer to live a solitary existence tucked away in dark, quiet places.
Unfortunately for humans, our homes provide a plethora of perfect hiding spots, and for this reason recluse spiders are primarily found indoors, most often in cupboards, inside and behind furniture (including beds) and in attics and basements. They are not aggressive and unless disturbed they will not go looking for trouble. Trouble finds them, however, usually when some unsuspecting human rolls over onto them while sleeping or puts on a piece of clothing in which the spider happens to be hiding. This is when the spider, suddenly facing the possibility of being crushed to death, will bite.
Immediate and Short-Term Effects of a Recluse Bite
There is usually no pain associated with a recluse bite at first; if there is, this will most often consist of a mild burning sensation. Over the next two to eight hours, however, the pain will intensify, sometimes to an excruciating degree. At the site of the bite an area of redness several centimeters across will usually develop, sometimes with a central area of paleness. Twenty-four hours out, a fluid-filled blister typically forms, surrounded by an area of inflammation. A measles-like rash may also appear on the surrounding skin. This may co-occur with a systemic flu-like syndrome involving fever, nausea/vomiting, muscle pain and malaise. In most cases, the effects of the recluse bite end there, and will resolve on their own in about a week.
Long-Term Complications of a Recluse Bite
A subset of bites, however, will become necrotic, meaning the affected tissue dies and begins to decompose, which then predisposes the victim to a number of secondary complications, the most dangerous of which is superimposed bacterial infection, which can enter the bloodstream through the damaged vasculature, spread throughout the body and result in coma or death. This, of course, is an extreme outcome, and exceedingly rare, particularly in areas having ready access to medical care.
Necrosis of a lesion, a process that occurs over the course of several days, will usually be heralded by a change of color at the center of the original lesion to a dusky blue or deep red, which may subsequently become numb as the nerve endings in the area die. A scab will then form that will ultimately break down into an ulcerated hole in the skin that will continue to grow over the first 10 days or so, usually to a size no bigger than 1 or 2 cm in diameter. A lesion this size will typically heal on its own over the next several weeks, frequently without scarring. Larger lesions, however, may take much longer to heal, and rare cases have been so large as to require surgical excision of necrotic tissue and skin grafting.