What genus contains black widow spiders?

The genus that contains black widow spiders is Latrodectus.

Latrodectus is a widespread genus in the cobweb-spider family Theridiidae. Its members are informally called widow spiders, and the group includes several species known as black widows, plus brown widows, redbacks, button spiders, and the New Zealand katipō. The genus was established by Charles Athanase Walckenaer in 1805.

North American black widows include the southern species Latrodectus mactans, the western black widow L. hesperus, and the northern black widow L. variolus. Females are often dark and may have a red or orange hourglass marking on the underside of the abdomen, although the pattern varies and is not a perfect identification rule.

Latrodectus venom contains latrotoxin, a neurotoxin that can cause latrodectism, including muscle pain, cramps, sweating, and spasms. Despite their reputation, bites rarely cause death, and the spiders are generally reluctant to bite unless threatened. The genus contains roughly three dozen recognized species, so “black widow” describes several species rather than one single animal.