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

Stegodyphus lineatus (Eresidae) is a desert spider that builds an aerial ca pture web on bushes in the Negev desert in southern Israel. Web building fo r 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 increas e in food intake causes spiders to reduce web renewal activity and web size . Alternatively, time constraints on foraging and development, resulting fr om a short growing season, could induce spiders to continue foraging even w hen supplemented with prey. The cost of web building was measured as time a nd mass loss. To build an average size web (about 150 cm(2)), 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 i n 2 different years. In 1994, they improved their condition compared to ind ividuals whose webs were removed to reduce foraging opportunities and compa red to control spiders. In 1995, spiders tested earlier in the season than the previous year did not improve their condition in response to prey suppl ementation. Nonetheless, in both years, food-supplemented spiders built sig nificantly 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 pot ential time constraints on foraging.