Black Widow Spiders: The Truth About the Bite and the Cannibal Myth

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In 1933 Alan Blair, a medical faculty member at the University of Alabama, held a black widow against his skin for ten seconds to document the bite and test whether repeated bites could build immunity. The pain, the rigid abdomen, and the soaring blood pressure were so severe that he refused a second bite and abandoned the experiment. The culprit is latrotoxin, a neurotoxin that forces nerve endings to dump their chemical messengers all at once, producing days of cramps, sweating, and a racing heart. The condition is called latrodectism, after the genus Latrodectus.

This episode sets the fear against the evidence. Only mature females can harm people, about 2,500 bites are reported to U.S. poison control centers each year, and no death has been recorded in the country since 1983. Antivenom mainly relieves pain, and one randomized trial found that standard pain medication did about as well. The conversation also takes apart the legend behind the name, describes how a nearly blind spider hunts by vibration and digests its prey outside its body, and recounts a taxonomic feud in which one scientist called another an ignoramus.

• Many bites are dry, with no venom injected, because venom is costly to make and a human is not prey.
• The idea that females always eat their mates came largely from caged laboratory spiders. In the wild, males read chemical cues in a female's silk to learn whether she has recently fed.
• Silk from the western black widow has a tensile strength of about 1,000 megapascals, comparable to steel wire of the same thickness and far stronger by weight.
• The genus was established in 1805, thrown into confusion by rival revisions in 1902, and sorted out in 1959 by Herbert Walter Levi, who studied female reproductive organs instead of color patterns.
• Science recognizes 35 widow species on every continent except Antarctica. They bite only when pressed against skin, and a blue mud dauber wasp hunts them.