Spider Bite FAQ

Kyoto: Hiking from Kibune to Kurama

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The female black widow typically is coal black and has a prominent, spherical abdomen that may be as large as one-half inch (1.25 cm) in diameter. This appearance is so distinctive that finding the characteristic markings on the undersurface of the abdomen is rarely necessary. The typical markings consist of red or orange figures that usually resemble an hourglass, but may be round, broken into two figures, or have some other configuration. Markings of the same color but in varying patterns are sometimes present on the back, although only the undersurface markings are considered characteristic. In some southwestern states black widow spiders have irregular white patches on their abdomens. Different species of Latrodectus in other countries have a similar appearance.

The black widow weaves a coarse, crudely constructed web in dark corners, both indoors and out. Almost half the black widow bites reported in the medical literature in the first four decades of this century were inflicted on the male genitalia by spiders on the underside of outdoor toilet seats. However, this spider is timid and would rather run than attack an intruder.

Thirty to forty years ago five to ten deaths a year resulted from black widow spider bites, although they were limited almost entirely to small children or elderly individuals in poor health. Recognition and treatment of such bites has improved so much that deaths are rare within the United States. (Bites in children weighing thirty pounds or less would still have a mortality of about fifty percent if untreated.) In healthy adults, black widow spider bites cause painful muscle spasms and prostration for two to four days, but complete recovery essentially always follows. Antivenin treatment is not recommended for adults.

The bite may feel like a pin prick, may produce a mild burning, or may not be noticed at all. Small puncture wounds, slight redness, or no visible marks may be found at the site of the bite. Within about fifteen minutes painful muscle cramps develop at the point of the bite and rapidly spread to involve the entire body. The characteristic pattern of spread is by continuity. From a bite on the forearm the cramps would spread to the upper arm, to the shoulder, and over the chest to involve the rest of the body, including the legs. The abdominal muscles are characteristically rigid and hard, although the abdomen is not tender. Weakness and tremors are also present. A typical subject is anxious and restless. A feeble pulse and cold, clammy skin suggest shock; labored breathing, slurred speech, impaired coordination, mild stupor, and rare convulsions (in children) suggest disease involving the brain. Bitten individuals are often covered with perspiration; dizziness, nausea, and vomiting are common. If the spider or its bite have not been observed, the signs and symptoms maylead to an erroneous diagnosis of an acute abdominal emergency. Symptoms typically increase in severity for several hours, occasionally as long as twenty-four hours, and then gradually subside. After two or three days essentially all symptoms disappear, although a few minor residua may persist for weeks or months.

Treatment consists of efforts to relieve the painful muscle spasms and antivenin for small children. No treatment at all should be directed to the site of the bite, with the possible exception of applying an ice cube to relieve pain. Incision and suction is damaging and useless and should not be performed.

Essentially nothing can be done outside a hospital; small children must be hospitalized. Antivenin, produced in the United States by Merck Sharp & Dohme, and the drugs to control spasms are rarely available anywhere else. The antivenin is prepared in horses and should not be given to persons allergic to horse serum. It is usually not administered to healthy adults between the ages of sixteen and sixty, and only to individuals of small body size with severe symptoms who are twelve to fifteen years old. Instructions with the vial of antiserum should be followed.

Muscle spasms may be relieved by periodic injections of 10 cc of a ten percent calcium gluconate solution or 10 cc of methocarbamol, but these are rarely available outside a hospital. A tranquilizer (diazepam) may help relieve less severe muscle spasms; hot baths are occasionally helpful. Strong analgesics are helpful but rarely provide complete pain relief.