Black widows (Latrodectus), on the other hand, can cause major havoc. "If there is one spider you have to worry about, this is the one," said Dr. Rangan. These bites can be fatal in small children or the frail elderly.
The bites are single needle-like puncture wounds. A quarter is dry bites that cause little harm, but 60% present with an erythematous macule, 30% with a "target" lesion, 5% with an erythema marginatum, and 5% with tiny distinct dual fang marks. "If you see a patch of sweat and a little red dot, it's virtually pathognomonic," said Dr. Rangan.
Symptoms begin 20 minutes to a few hours after the bite. Cramping moves quickly to the abdominal wall where it can resemble a wide range of other syndromes. Pain can be severe and may be accompanied by headache, diarrhea, diaphoresis, photophobia, dyspnea, nausea, vomiting, and agitation.
It's important to administer the antivenom quickly. In this case, it is equine-derived, so it can cause anaphylaxis in allergic patients. A skin test is available.
Antivenom may relieve symptoms quickly, but in the meantime, you can control pain with diazepam or morphine. Calcium gluconate and methocarbamol have been used in the past for black widow bites, but Dr. Rangan advised against them.
When it doubt, he urged, call Poison Control at 800-222-1222, a national hotline.
Dr. Rangan said he had nothing to disclose.