Previous foraging success influences web building in the spider Stegodyphus lineatus (Eresidae)

Stegodyphus lineatus (Eresidae) is a desert spider that builds an aerial capture web on bushes in the Negev desert in southern Israel. Web building for spiders is costly in energy, time, and risk of predation. Spiders should trade-off these costs with the benefits in terms of prey capture. We tested the hypothesis that the previous foraging success of the spider influences the effort invested in foraging. Specifically, we asked whether an increase in food intake causes spiders to reduce web renewal activity and web size. Alternatively, time constraints on foraging and development, resulting from a short growing season, could induce spiders to continue foraging even when supplemented with prey. The cost of web building was measured as time and mass loss. To build an average size web (about 150 cm²), we calculated that a spider requires 6 h and that spiders lose 3%-7% of their weight. In field experiments, spiders responded differently to food supplementation in 2 different years. In 1994, they improved their condition compared to individuals whose webs were removed to reduce foraging opportunities and compared to control spiders. In 1995, spiders tested earlier in the season than the previous year did not improve their condition in response to prey supplementation. Nonetheless, in both years, food-supplemented spiders built significantly smaller webs than food-deprived and control spiders. This result was confirmed in a laboratory experiment where prey intake was controlled. We conclude that for S. lineatus immediate foraging risks outweigh the potential time constraints on foraging.