WESTERN BLACK WIDOW

Scientific name

Latrodectus hesperus

Size

The average size of mature, female Western Black Widow spiders is approximately .5 inch, with a leg span of 1.5 to 2 inches. Mature, male Western Black Widow spiders are much smaller - approximately 1/3 the size of the female.

Description

Western Black Widow spiders are a glossy jet-black, with a bright-red hourglass marking on the underside of their abdomen. The hourglass of the Western Black Widow is typically complete, with the bottom half (farthest from the head) typically being slimmer and not as wide as the top half of the hourglass.

In addition to the typical hourglass marking on the underside of their abdomen, immature Black Widow spiders can vary greatly in the way they are marked on the top of their back. Typically they have red or white spots running down the middle of their back. Sometimes they will also have red and white markings patterned down the sides of the abdomen.

Distribution

The Western Black Widow is found throughout the western United States, being most common in the southwest states. Outside of the United States, the Western Black Widow is found in Southwestern Canada and in Mexico.
Map of US states the Western Black Widow is found in.
Map does not show area of true distribution, only the states in which there is a population.
Actual distribution in any highlighted state may be limited.

Notes

As with all widow spiders, only the female of the species is considered dangerous. The much smaller male is considered harmless. Western Black Widow spiders are nocturnal, which means they are active during the nighttime. They spend most of their time hanging "upside down" in their web, which often makes the hourglass marking immediately visible.

Western Black Widow spiders are typically not aggressive, and bite as a defensive measure when they are attacked or feel threatened. They will often retreat into hiding, but are more protective of their web when there are egg sacs present.

Western Black Widow
Photo used by permission:
© Jim Kalisch
Department of Entomology, University of Nebraska-Lincoln

Web

The web of the Western Black Widow does not resemble the typical spider's web, such as the garden spider's web, that is often associated with spiders. It instead resembles a cobweb, constructed of very strong white silk. The web will often be constructed under rocks or logs, or in large cracks and crevices, where it will be dark and the web will be protected from the weather. Webs will sometimes be constructed on lawn furniture, wood piles, sheds, barns, and in garages as well.

For more information on dangerously venomous spiders, please see the Venomous Links page.

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