Latrodectus is a genus of spider in the big spider family Theridiidae, most of which are commonly known as widow spiders. The genus contains 33 recognized species distributed worldwide, including the North American black widows (L. mactans, L. hesperus, and L. variolus), the button spiders of Africa, and the Australian redback. Species vary widely in size. In most cases the females are dark-colored and readily identifiable by reddish hourglass-shaped markings on the abdomen.
The venomous bite of these spiders is considered particularly dangerous because of the neurotoxin latrotoxin, which causes the condition latrodectism, both named for the genus. The female black widow has unusually large venom glands and its bite can be particularly harmful to humans. However, despite the genus' notoriety, Latrodectus bites are rarely fatal. Only female bites are dangerous to humans. However, there is no way of telling whether an individual is male or female until diagnosed.