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 A black widow hanging upside down in its web. The red hour glass marking is clearly visible on the abdomen. Courtesy of Wikimedia Commons.
The black widow (genus Lactrodectus) is famous for its potent venom. However, due to their small size the bites are rarely fatal. But since they are common and a large geographical distribution (they are found on all continents, although only in the southern parts of Europe and Asia), they are the spiders responsible for most human deaths world wide. Black widows build 3-dimensional cobwebs consisting of a sheet of silk, supporting threads and sticky threads extending to the substrate, where they catch passing insects.
Biologists from the University of Akron in Ohio starved individuals of the western black widow (Lactrodectus hesperus) and compared its web-building and prey catching behaviour with well-fed spiders in the laboratory.
They found that hungry spiders build web with a clear distinct sheet and many sticky threads whereas well-fed spiders build a more disorganised 3d web with many criss-crossing threads. The scientists, furthermore, showed that both hungry and fed spiders were better at catching crickets in webs build by hungry spiders.
So why do satiated spiders build less efficient webs? Probably because they require less prey, but also because the criss-crossing threads most likely provide much more defence from predators than the webs build by hungry spiders. Thus web structure in widow spiders seem to be a compromise between safety and food, where the internal state of the spider determines toward which parameter the web is optimised.
Source:
Zevenbergen, J. M., Schneider, N. K. and Blackledge, T. A. (2008). Fine dining or fortress? Functional shifts in spider web architecture by the western black widow Lactrodectus hesperus. Animal Behaviour 76, 823-829.
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