Figure 1

Aggression in queenless worker groups. The number of aggressive behaviors (sum of humming, darting and attack events) during 60 minutes performed or received by callow workers that were kept for 4 days. Observations were performed during days 3-4 after group establishment. Each group is composed of full sisters originating from a different colony (except for one, n = 15 groups, 14 colonies). Data are presented as means ± SE.