COSTS AND BENEFITS OF GROUP LIVING FOR PHOLCID SPIDERLINGS - LOSING FOOD, SAVING SILK

Holocnemus pluchei (Scopoli) spiderlings may either live alone or share webs with larger conspecifics. Three lines of evidence indicate that group-living spiderlings capture less food than do solitary spiderlings: (1) in field surveys, spiderlings in group webs were seen feeding less often than those living alone; (2) spiderlings in group webs had relatively smaller abdomens than did solitary individuals, indicating that recent foraging success had been poorer; and (3) when prey were introduced into group webs, the largest spider in the web that detected the prey won the prey approximately 77% of the time. In spite of this cost, spiderlings were found in groups more often than expected by chance. This observation may be explained by the high energy cost of constructing solitary webs, as demonstrated by (1) bomb calorimetry and (2) a web-removal experiment, which showed that spiders forced repeatedly to rebuild webs grew more slowly and were smaller than controls. The main benefit of group living is likely to be the reduction of the cost of web building when spiderlings take advantage of webs built by larger conspecifics. © 1991 The Association for the Study of Animal Behaviour.