The Spider's Guide to Preda­tor De­cep­tion

by Elio

We some­times make a sally into the high jinks of meta­zoans, per­haps to per­suade you that we are not pro­kar­yotic chau­vin­ists (not that you thought so, surely). This foray con­cerns a novel strat­egy that sheds light on an ap­par­ent para­dox: many prey, in­stead of mak­ing them­selves hard to see, seem to use tac­tics that make them easy for the preda­tors to spot. To wit, cer­tain fish, am­phibians, rep­tiles, and in­sects are strik­ingly col­ored or are oth­er­wise con­spic­u­ous, which poses a Dar­win­ian para­dox. The way out? Lure the preda­tor into at­tack­ing a de­coy! Here is a story of spi­ders that make spi­der de­coys. And the de­coys work.

C. mul­meinen­sis. (Right) de­coys of prey pel­lets and egg sacs. Sour­ces: Matt Walker, ed­i­tor, Earth News, LibyMax.ru

A spi­der called Cy­closa mul­meinen­sis uses egg sacs and the left­over car­casses of its prey to make con­structs that re­sem­ble its own body. These struc­tures are strung along one of the guy wires of the web, which has earned this species the la­bel Trash Line Spi­ders. Spi­der ex­perts Ling Tseng and I‑Min Tso of Tung­hai Uni­ver­sity in Tai­wan ob­served that par­a­sitic wasps at­tacked the de­coys more of­ten than the spi­ders. The au­thors quant­itated the cost and ben­e­fits of this be­hav­ior and con­cluded that "this con­spic­u­ous an­tipreda­tor dis­play would en­hance over­all sur­vival and was adap­tive for this vul­ner­a­ble prey." Thus, this stra­tegy of fool­ing the preda­tor rather than hid­ing from it seems to work. It may ex­plain in part why so many spi­ders dec­o­rate their webs, some­thing that has baf­fled arach­nidol­o­gists for a long time. Some­times in-your-face strate­gies work pretty well.