Deciding where to settle: conspecific attraction and web site selection in the orb-web spider Nephilengys cruentata

Abstract

Although there is some evidence that web-building spiders are more likely to select habitats where conspecifics are present, the mechanisms underlying the attraction to conspecifics remain poorly understood. One hypothesis is that the presence of conspecifics is an indirect signal of good habitat quality. Alternatively, the presence of other webs could improve the structural suitability of the site for the construction of new webs, by increasing the number of anchorage points necessary for web support. We tested these hypotheses in the orb-weaving spider Nephilengys cruentata in a seminatural field situation. We released females inside individual enclosures and recorded where they settled. The enclosures were provided with either (1) small and flat cotton-like fragments of newly built webs from conspecifics or (2) artificial threads attached to their walls, providing additional structural support for the construction of the web. Spiders were significantly more likely to settle inside those cages containing silk from conspecifics than in vacant control enclosures, and the silk was not used for the construction of the web. The presence of artificial threads, in turn, did not increase their probability of settlement. Our results indicate that conspecific attraction in N.cruentata is not only a by-product of direct benefits that existing webs may provide, but can also follow from the use of silk as an indirect predictor of habitat quality.