Claim: There are different species of spiders.

Latrodectus is a genus of spiders in the family Theridiidae , most of which are commonly known as widow spiders . The genus contains 31 recognized species distributed worldwide , including the North American black widows -LRB- L. mactans , L. hesperus , and L. variolus -RRB- , the button spiders of Africa , and the Australian redback spider . 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 after 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 .