Field Guide to Venomous and Medically Important Invertebrates ...

Black widow spiders and their relatives (Latrodectus spp.) are among the most dangerous spiders
to humans. Although timid and reclusive in behavior, they can inflict painful and potentially
deadly bites when provoked or accidentally contacted. These spiders often are shiny black in
appearance and approximately one inch or less in body length. Most widow spiders have the
ventral (bottom) side of the abdomen is variously marked with red spots or other shapes, and
some species may also have similar markings on the dorsum (top side). The red hourglass
marking of the southern black widow, Latrodectus mactans, in North America, and the red
dorsal spot of the redback, Latrodectus hasselti, in the Austro-Asian region are perhaps the most
well known of such markings among these spiders. Approximatley 40 species of ―black
widows‖ occur worldwide. Medically important species occur in the Middle East, Europe,
Madagascar, Africa, Asia, Australia, and throughout the Western Hemisphere. Geographically
unique common names applied to the black widows include shoe-button spider (South Africa),
katipo (New Zealand), redback (Australia), and malmignatte and karakurt (Europe). Other
species of Latrodectus of concern that are not black in color include the brown widow (tropical
areas worldwide; common in the southern United States), red widow (central and southern
Florida, Africa), and northern widow (northern Florida to Canada).
Figure 2. Southern black widow (Latrodectus mactans), North America. Photo: Texas Parks &
Wildlife Department.
Figure 3. Web of southern black widow (Latrodectus mactans) showing irregular pattern of silk
threads. Photo: David Bowles & Mark Pomerinke.
Figure 4. Red back (Latrodectus hassleti), Australia. Photo: source unknown.
Figure 5. Brazilian black widow (Latrodectus curacaviensis), South America. Photo: source
unknown.