An anti-adhesive surface coating reduces adhesion during contact with cribellar threads in Pholcus phalangioides (Araneae, Pholcidae) but not in the web-owning spider Uloborus plumipes (Araneae, Uloboridae)

Cribellar threads are powerful tools for web spiders to catch and retain prey. Spiders encountering such threads, like cribellar web spiders or araneophagic spiders invading cribellar webs, should have a protective mechanism against the adhesion of these threads. We tested for an anti-adhesive surface coating in the web invader Pholcus phalangioides and the cribellate orb weaver Uloborus plumipes. We calculated an index of adhesion for differently treated legs of the two species in a cribellar U. plumipes capture thread, i.e. untreated legs, water-washed legs, and legs washed with the organic solvent n-hexane. The results show that legs of P. phalangioides stick significantly stronger when washed with n-hexane. Our interpretation is that P. phalangioides has an organic surface coating lowering the adhesive force of the cribellar thread. No such mechanism was found in U. plumipes.