LOPEZ, Y.; MOORE, A.M.F.: Assessing the Weight that Black Widow Gumfoot Lines Can Pick Up
Like other theridiid spiders, the black widow (Latrodectus hesperus) constructs gumfoot lines at the bottom of its cobweb. Gumfoot lines are vertical strands of silk that are tautly attached to the surface and detach easily when an insect touches them. Sticky droplets on the gumfoot line pull the insect into the air. Provided the insect is small enough, gumfoot lines are effective traps. In this study, we determined how much weight can be picked up by gumfoot lines. 27 black widows were housed separately. They were given wooden frames to encourage construction of gumfoot lines of uniform 10 cm length. We constructed 20 weights, ranging from 1-20 mg, out of insulated copper wire. We rolled each weight into 100 different gumfoot lines. The gumfoot lines either (1) broke, without lifting the weight, (2) broke and lifted the weight or, (3) attached to the weight but did not break. As the weight increased the percentage of threads that broke without lifting the weight increased, as did the percentage of threads that attached to the weight but did not break. As the weight increased a smaller percentage of gumfoot lines picked up the weight. The 1 mg weight was picked up by 95% of the threads while the 20 mg weight was picked up by 3% of the threads. The percentage of threads that pick up the weight appears to decrease logarithmically (R2 = 0.93) as the weight increases. Thus, gumfoot lines seem to be an effective trap for insects of 10 mg and smaller. Tests of live insects are ongoing. (NSF DBI-9996072).
