Black widow spider

Latrodectus spp.

Black widow spiders are found throughout the world and are commonly associated with urban habitats or agricultural areas.   In California, we have two species of black widow spider.

When thinking about black widows, most people picture the females—they are shiny black with long legs and a red (or sometimes white or yellow) marking, resembling an hourglass, on the underside of the abdomen.  Male black widows are half the size of the females and are usually dark brown with varying colors of stripes/dots and do not have the hourglass mark.

Although supposedly named for their habit of eating their mates, very rarely does the female eat the male after mating.  This may happen if she mistakes the male for a prey item, or if there is a shortage of food.

The black widow spider is notorious for its neurotoxic venom.  Females, being larger than males, are more potentially dangerous.  As with many venomous animals, brightly colored markings serve as a warning to predators.  Females purposely hang upside down so their hourglass marking is visible.  Eating a black widow is usually not deadly for a small predator (birds, lizards, etc), but the sickness that follows the encounter is enough for the animal to remember that the bright marking means “do not eat.”

Worldwide, less than one percent of people who are bitten die from black widow venom.  The initial bite of a black widow may feel like a pin prick.  Afterwards, a victim may experience pain in the vicinity of the bite followed by muscle aches, severe abdominal pain, vomiting, muscular cramping, sweating, fever, and headache.  There is usually no swelling of the bite area, but a small lesion may form.  If you have been bitten by a black widow spider, seek medical attention.

Female black widows rarely leave their web unless disturbed.  To avoid being bit, be cautious when picking up or moving objects around sheds, woodpiles, or garages— usually a spider will only bite people in defense when its web is disturbed.

Black widows are voracious consumers of insects, especially flies and crickets, and are an important part of the environment around us.