Posted for Emma Marris

Black widow spiders, Latrodectus Hesperus, weave two different types of web, depending on whether they are ravenously licking their fangs in anticipation of hapless prey or curling up with a full belly.

University of Akron researchers, working with hundreds of hungry and full black widows, showed that the starving spiders wove webs of “sticky gumfooted threads” in more or less a single dimension. The stickiness ensnares insects. Satiated spiders wove “nonsticky, tangle-based webs” in which to chill out and avoid predation. They controlled for the possibility that the “fed” spiders were larger by starving big ones and feeding little ones. See the paper and the University of Akron’s story on it.

Black widow webs aren’t your classic Charlote’s Web web—those are woven by orb-weaving spiders. The black widow is a cobweb spider.

This isn’t the first study on web design and spider hunger. In 2000, Takeshi Watanabe of Kyoto University looked at an orb-weaving spider called Octonoba sybotides and found that “The spider appears to increase the tension of the radial threads so that it can sense smaller prey better when hungry.”

Octonoba sybotides weaves webs with aesthetic little flourishes that give them quite a bit of style. These flourishes are called “stabilimenta” because they were once proposed to be stabilizing elements in web design. See some examples of spiral, zigzag and wiggedy egg shape.

Todd Blackledge, the researcher behind the black widow study, has looked at these stabilimenta too. They seem to be irresistible to spider scientists. “They have been a really classic problem in arachnology,” says Blackledge. His theory is that are defensive (the might camouflage the spider or startle or warn off potential predators), but others still like the idea they attract prey. The debate rages on.

Meanwhile, in the familiar “they are more afraid of you than you are of them” mode of all scientists studying creepy things, Blackledge tells The Great Beyond that his black widow subjects were “amazingly docile”. Tell that to Spider Man.

” Western black widow cobwebs consist of up to four regions of silk. The spider manoeuvres on a sheet of silk (SH) that is supported by an array of threads (ST). Sticky gumfooted threads (GF) run from the sheet to the substrate and are coated with glue near their base. Spiders typically hide in a retreat during the day and move out onto the sheet when actively hunting at night. (a) Starved spiders spin webs that contain all four components. (b) Satiated spiders spin webs that typically contain more supporting threads and lack both sticky gumfooted threads and defined sheets of silk.” – from the research paper (doi:10.1016/j.anbehav.2008.05.008).

Photo: University of Akron