San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide
Adult female Agelenopsis aperta, copyright Jim Berrian
Adult male

Steatoda grossa
False Black Widow

THERIDIIDAE

Description

Females measure 5.9-10.5mm in length. The carapace is black and unmarked. The abdomen is purplish brown with light marks; a semicircular band of light marking is formed on the anterior edge of the abdomen with three medial light marks behind. There also may be light marks found laterally. Males are smaller, measuring 4.1-7.20mm in length; the body is thinner and more elongate than the female's, but the color pattern is similar.

Adult female Agelenopsis aperta, copyright Jim Berrian
Adult female
Range and Habitat

In the United States, False Black Widows occur in southern coastal states and west coast states ranging south into Baja California, Mexico. In San Diego County they are found in lower coastal habitats. These spiders are common around dwellings and gardens as well as under rocks and wood.

Natural History

False Black Widows may live to six years old. The name, "false widow," is used because at first glance these spiders look like black widows; they build widow-like webs, and live and habitats typical of black widows.

Related and Similar Species

The black widow, Latrodectus, is similar in shape and dark color but the red hourglass abdominal mark is lacking in Steatoda.

References

Kaston, B.J. 1978. How to know the spiders, 3rd Ed., 272pp.

Levi, H.W. 1957. The spider genera Crustulina and Steatoda in North America, Central America, and the West Indies (Araneae, Theridiidae). Bull. Mus. Comp. Zool. 117(3):367-424.

Text by Jim Berrian. Photo © Jim Berrian.

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