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Spider Bites


A spider bite is the puncture wound produced by the bite of a spider - an arachnid related to ticks and mites.

Fewer than 100 of the some 30,000 species of spiders are known to bite. Two of them, the black widow spider and the brown recluse spider, found in the U.S., are poisonous.

Lactrodectism is the clinical syndrome that follows envenomation by the black widow spider.

Arachnidism is the name given to systemic symptoms resulting from the bite of any member of the class, Arachnida, which includes spiders, scorpions, ticks and mites.


Spider bites are rare but can be very serious. The female black widow spider accounts for most of them. This spider is glossy black with a body of approximately one-half inch in diameter, a leg span of about two inches, and a characteristic red hourglass mark on the abdomen.

The black widow spider is found in woodpiles, sheds, basements, or outdoor privies. The old-fashioned outdoor privy, a favorite nesting site, gained the black widow its greatest notoriety. At one time, buttocks and genitals were the most common sites of envenomation. Since the advent of indoor plumbing, bites to the extremities are more common and tend to occur when the spider is accidentally squeezed against the body.

In temperate climates most bites occur in the warmer months; bites occur year-round in tropical areas. Men are more likely to be bitten than women, perhaps because of the greater likelihood of contact in outdoor settings.

Brown recluse spiders (loxosceles reclusa) cause painful bites and serious local reactions, but are not nearly as dangerous as black widows. Brown recluse spiders are slightly smaller than black widows; they have a white "violin" pattern on their backs. This type of spider is very reclusive and most people are not even aware that they have been bitten.

Initially, there may be an itch and a small puncture from the spider bite but within a few hours local skin reactions may appear, including minor pain, swelling, and discoloration around the bite where the venom was injected. This requires a trip to the doctor or emergency room.


The bite is often painless and the first sign may be cramping abdominal pain. The abdomen becomes hard and boardlike as the waves of pain become severe. Breathing is difficult and accompanied by grunting. There may be nausea, vomiting, headaches, sweating, twitching, shaking, and tingling sensations of the hand. The bite itself may not be prominent and may be overshadowed by the systemic reaction.


The toxin of most species causes only local pain, redness and swelling. That of the more venomous black widow causes generalized muscular pains and spasms, and rigidity.

Black widow bites

For black widow spider bites, pain may be relieved with parenteral narcotics or muscle relaxants (e.g., methocarbamol - Robaxin, and diazepam - Valium). Calcium gluconate 10 percent given intravenously may relieve pain and muscular rigidity. Antivenin is rarely indicated, usually only for the very young or elderly patients who do not respond to initial measures.

Specific antivenin (Antivenin Lactrodectus Mactans) is derived from horse serum. Black widow spider bite therapy requires only a single 2.5ml vial of Lactrodectus antivenin. Assessment of horse serum sensitivity is essential prior to antivenin use.

Brown recluse bites

Because bites occasionally progress to extensive local necrosis, some authorities recommend early excision of the bite site, whereas others prefer oral corticosteroids. Interest has also focused on the use of dapsone and colchicine.


Is it a spider bite?

Is it a black widow bite?

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Can you prescribe medication to relieve the pain and relax the muscles?

Is antivenin therapy necessary?

What are the risks and side effects?

What can be done to prevent further bites?