San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide

Latrodectus hesperus
Black Widow Spider

THERIDIIDAE

Description

Also called the "hourglass" or "shoe-button" spider, a name derived from the crimson markings on the underside of the abdomen.

The adult female has a unique shiny black and bulbous abdomen and may reach a length of 1-1/4 inches. The smaller, 1/4-inch-long male is brown with red and white markings, including the abdominal hourglass design.

This spider produces a neurotoxic venom 15 times more virulent than an equal amount of rattlesnake poison. Despite this distinction, only one death every five years in the United States can be attributed to this spider because few people are bitten and little venom is injected with each bite.

Range and Habitat

The Black Widow spider is common throughout the southern United States. Webs can be found in undisturbed, recessed areas including woodpiles, garages, fence rows, debris and abandoned animal burrows.

Natural History

In the summer, after mating and perhaps, but not always, making a meal of the male, the female will begin constructing a number of egg sacs, each containing 50 to 250 eggs. The whitish spiderlings hatch within a few months. They begin feeding and gradually develop into adults in one to two years; some females live as long as three years.

The black widow conceals itself in a funnel-shaped retreat connected to an irregular mesh of coarse silk close to the ground where it entangles prey: cockroaches, earwigs and crickets.

If not for their potent venom, black widows probably would be considered beneficial because they help control a number of insect pests. However, this is not the case.

[Photo of a Black Widow spider.]
Adult female Latrodectus hesperus, copyright Jim Berrian
Adult female


The best method to protect yourself from accidental contact with these spiders is to wear gloves when cleaning cluttered yards or storage areas. Keep in mind that where there is a web, a spider may not be far away. Individual black widows should be caught and disposed of carefully.

David Faulkner, Research Associate, Entomology Department

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