Latrodectism is the illness caused by the bite of Latrodectus spiders (the black widow spider and related species). Pain, muscle rigidity, vomiting, and sweating are the hallmarks of latrodectism. Contrary to popular conception, latrodectism is very rarely fatal to people. Domestic cats have been known to die with convulsion and paralysis.
There are several spider species all named black widow: southern black widow spider (L. mactans), the European black widow(L. tredecimguttatus), Western black widow spider (L. hesperus), Northern black widow spider (L. variolus). Other Latrodectus that cause latrodectism are the Australian redback spider (L. hasselti), and the katipo spider (L. katipo). Several other members ofLatrodectus genus are not commonly associated with latrodectism including the cosmopolitan brown widow (L. geometricus).
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http://www.aafp.org/afp/2007/0315/p869.html common spider bites james h. diaz, m.d., dr.p.h., m.p.h.t.m. and kim edward leblanc, m.d., ph.d., louisiana state university school of medicine, new orleans, louisiana am fam physician. 2007 mar 15;75(6):869-873.