In most cases, the females are dark-coloured and can be readily identified by reddish markings on the central underside (ventral) abdomen, which are often hourglass-shaped.

These small spiders have an unusually potent venom containing the neurotoxin latrotoxin, which causes the condition latrodectism, both named after the genus.

[9][10] The prevalence of sexual cannibalism, a behaviour in which the female eats the male after mating, has inspired the common name "widow spiders".

Black widow spiders prefer to nest near the ground in dark and undisturbed areas, usually in small holes produced by animals, or around construction openings or woodpiles.

As with other web-weavers, these spiders have very poor eyesight and depend on vibrations reaching them through their webs to find trapped prey or warn them of larger threats.

The blue mud dauber species, Chalybion californicum, is a wasp that, in western North America, is the primary predator of black widow spiders.

[1][25] Arachnologist Herbert Walter Levi revised the genus in 1959, studying the female sexual organs and noting their similarity across described species.

Cambridge questioned Dahl's separating species on what he considered minor anatomical details, and the latter dismissed the former as an "ignoramus".

[26] The most prevalent species occurring in eastern Asia and Australia is commonly called the redback (Latrodectus hasselti).

[29] In 1933, a University of Alabama medical faculty, Allan Blair conducted an experiment on himself to document the symptoms of a black widow bite, and to test whether someone can build immunity after being bitten.

[30] The effects of the bite were so painful and harsh that Blair failed to complete the experiment and did not follow through with being bitten a second time.

In the United States, no deaths due to black widows have been reported to the American Association of Poison Control Centers since 1983.