Food consumption rates and competition in a communally feeding social spider, Stegodyphus dumicola (Eresidae)

A major factor which affects an animal's consumption rate is competition fo r food items. Competition usually results in a drop in consumption rate; ho wever, this may be counteracted if the animals can exploit the foraging eff orts of others, as could occur in social spiders when feeding on the same p rey item. Spiders digest prey extra-orally and might utilize the enzymes or digesta produced by other individuals feeding from the same prey item. We investigated prey consumption in the social spider Stegodyphus dumicola to determine if the rate of consumption of individual spiders changed in the p resence of competitors. We found that when one spider fed on small prey, fo od consumption rate decreased with feeding duration. When the prey was larg er in relation to the spider there was an initial delay in consumption. The re was no apparent advantage for a second spider to feed on a prey item alr eady being consumed: the second spider fed for less time and gained less ma ss. These results indicate that social spiders compete during the process o f food ingestion and the presence of another spider reduces the value of th e prey item to a subsequent forager.