An organic coating keeps orb-weaving spiders (Araneae, Araneoidea, Araneidae) from sticking to their own capture threads

More than 95% of orb-weaving spider species ensure prey capture success by producing viscous threads equipped with gluey droplets. However, this trap may bear serious risks for the web-inhabiting spider as well. The obvious question, how a spider avoids getting stuck in its own capture spiral, has gained little scientific attention up till now. In 1905, the French naturalist Jean-Henry Fabre concluded from anecdotal observation that orb-weaving spiders protect themselves by a fatty surface coating. Here, we test this hypothesis by indirectly measuring the force necessary to detach an autotomized spiders leg from the capture spiral of its own web (here called index of adhesion, IOA). Three groups of legs, each of the species Araneus diadematus Clerck, 1757 and Larinioides sclopetarius (Clerck, 1757), were tested. One was left untreated, one was washed with distilled water (H2O), and one was washed with the organic solvent carbon disulphide (CS2). In both species, we found a weak IOA between the spider leg and the gluey capture spiral in untreated and water-washed legs without significant differences between the two. The IOA approximately doubled, when spider legs had been washed with carbon disulphide prior to measurement, that is, the CS2-washed legs stuck significantly more strongly than the untreated and water-washed legs. These results provide indirect evidence for a protective anti-adhesive organic coating on the spiders body surface and so support Fabres hypothesis.