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Spider Bites

Over 100,000 species of spiders are found worldwide. Nearly all possess poison glands, but most are harmless to humans All spiders are carnivorous and secure live prey either by hunting or trapping spider bites, stings. Trappers (eg, black widows) spin webs to trap prey, which they envelop in a

In the United States, the most common medically significant spider bites are from widow spiders ( Latrodectus mactans ) and brown recluse spiders (Loxosceles reclusa). Less common but significant spider bites are reported from tarantulas (Theraphosa), running spiders (Chiracanthium species), wolf spiders (Lycosa), black jumping spiders (Phidippus), and hobo spiders (Tegenaria agrestis ) .

Physicians need to be able to recognize the signs and symptoms of medically significant venomous spider bites, because an inaccurate or missed diagnosis may lead to significant morbidity and mortality. Since the spider responsible for the bite is often not seen or recovered for identification, knowledge of physical descriptions as well as

Widow spider

Widow spiders are found throughout temperate and tropical areas of the world. Classic black widow females are much larger than males. As they age, brightly colored immature females become globular and shiny black, with the well-known red hourglass mark on the ventral surface (figure 1). Females are trappers and inhabit sites such as


Symptoms of latrodectism (the clinical syndrome resulting from the bite of widow spiders) are caused by a potent neurotoxin that disrupts subcellular organelles in presynaptic nerve terminals. This results in an excess of various neurotransmitters in the synaptic junctions, causing catecholamine release at adrenergic nerve endings and


Treatment goals are pain relief and reversal of neurotoxin action. Intravenous calcium gluconate has been widely used for pain relief. However, because relief is often short-lived and repeated injections are required, investigators have

Brown recluse spider

Brown recluse spiders have been reported throughout the United States, although they are most heavily concentrated in the South, where the climate is mild. The body shape is typically slender and often bears a violin-shaped marking on the dorsum, thus the common names "fiddle-back spider" and "violin spider". The female may be twice the length


Treatment regimens vary, but supportive treatment with rest, local application of ice, immobilization, and elevation is adequate for most mild to 

Early surgical excision of the wound has been suggested in severe bites, although it is controversial. Corrective surgery with skin grafting after eschar formation has 

Dapsone, which inhibits polymorphonuclear leukocytes (a major component of skin necrosis), has been shown to be effective in treatment of cutaneous loxoscelism. Patients are given 50 to 100 mg orally twice a day until 


Tarantulas are the largest spiders, and more than 30 species inhabit the United States, primarily in the Southwest. These nocturnal hunters seek mainly beetles and grasshoppers. Sexual dimorphism is subtle and is 

Running spider

Running spiders are small (7 to 10 mm) and range in color from olive green to pale yellow or brown. Only three of the 160 reported species inhabit the continental United States, but all three are widely distributed and have been

Wolf spider

Wolf spiders reside in grassy areas throughout most of the United States. These medium-sized (3.5-cm) spiders have elongated, cylindrical bodies. It was once thought that they hunted in packs and ran down their prey. On the

Black jumping spider

About 50 to 60 species of black jumping spiders are found in North America. They have short legs and bodies, which are typically brightly colored with white stripes and bands on the ventral aspect. These spiders can jump 40 or

Hobo spider

Fast-moving hobo spiders, also known as aggressive house spiders, are large and brown with gray markings. These spiders are distributed throughout much of the Northwest and are rarely found above ground or basement level. Their webs are usually located in dark, moist areas, such as woodpiles, crawl spaces, and along foundations.

These common biters are easily provoked and aggressive when crowded, especially from midsummer through fall, when the male wanders in search of a mate. Diagnosis of the bite can be difficult because, as with most spider bites, the culprit is rarely seen or recovered. In addition, the ulcerating bite of hobo spiders is similar to that of