Evidence for Preadaption to Sociality in the Solitary Spider, Steatoda Triangulosa (Araneae, Theridiidae)

Steatoda triangulosa is a solitary domestic spider. In the laboratory, newly hatched Steatoda triangulosa spiderlings attacked and fed on prey organisms as a group. Kullman (1972) recognized three characteristics necessary to classify a spider as social: tolerance. interattraction and cooperation. Laboratory studies were conducted to test the hypothesis that Steatoda triangulosa may be preadapted to sociality according to these criteria. The group response was demonstrated by plotting the position of caged spiderlings in relation to a prey item before and after feeding. The intensity of the response was inversely proportional to the distance of the spiderlings from the prey. In studies to investigate cooperative feeding, spiderlings responded in greater numbers to larger prey. When presented with three similar -sized prey simultaneously, spiderlings responded significantly more often to one prey item than to more than one. To investigate tolerance, groups of spiderlings were kept for 21 days under different prey densities, and under conditions of high and low relative humidities. Cannibalism was inversely proportional to prey density. Increasing humidity decreased the incidence of cannibalism in groups of starved spiderlings