There is one species of spider.
Latrodectus is a genus of spiders in the family Theridiidae , most of which are commonly known as widow spiders . Spider . They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms . In all except the most primitive group , the Mesothelae , spiders have the most centralized nervous systems of all arthropods , as all their ganglia are fused into one mass in the cephalothorax . A minority of species are social , building communal webs that may house anywhere from a few to 50,000 individuals .