Accidents caused by the bite of spiders of the genus Latrodectus have been known since olden times (22), being rather frequent in the United States, Chile, Colombia, Guatemala, Mexico, Uruguay and Argentina (Latrodectus mactans); Australia and New Zealand (Latrodectus hasseltii); Italy, Spain and Russia (Latrodectus tredecimguttatus); South Africa (Latrodectus indistinctus) and Madagascar (Latrodectus menavodi). In Argentina we have recorded hundreds of cases (Latrodectus mactans).
Eight species of this genus have been described: Latrodectus pallidus (Cambridge, 1872); L. hystrix (Simon, 1889); L. tredecimguttatus (Rossi, 1770); L. geometricus (Koch, 1841); L. foliatus (Mello Leitao, 1940); L. concinnus (Cambridge, 1905); L. indistinctus (Cambridge, 1905) and L. mactans (Fabricius, 1775). L. pallidus, L. hystrix, L. geometricus and L. mactans ought to be considered as fundamental species (11). The 12,000 spiders used in our investigations belonged to the species L. mactans (Gerschman and Schiapelli). We also experimented with L. geometricus.