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 for food items. Competition usually results in a drop in consumption rate; however, this may be counteracted if the animals can exploit the foraging efforts of others, as could occur in social spiders when feeding on the same prey 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 presence of competitors. We found that when one spider fed on small prey, food consumption rate decreased with feeding duration. When the prey was larger in relation to the spider there was an initial delay in consumption. There was no apparent advantage for a second spider to feed on a prey item already being consumed: the second spider fed for less time and gained less mass. These results indicate that social spiders compete during the process of food ingestion and the presence of another spider reduces the value of the prey item to a subsequent forager.