Division of labour and specification of castes in the red imported fire ant Solenopsis invicta buren

Division of labour in Solenopsis invicta follows a familiar pattern: younger, smaller ants tend toward brood care while older, larger ants tend toward foraging. However, long-term observations of marked individuals reveal that length of nursing and foraging ‘careers’ and the age of transition between these activities vary considerably between and within size groups, and are related to length of life. Experiments with entire colonies show that larger ants are more likely than smaller ants to forage for insect prey. There are two main worker castes, ‘nurses’ and ‘foragers’, whose members span a wide age-size range, and a large ‘reserve’ subcaste, heterogeneous in age, size, and behaviour: reserves may nurse, forage, store liquid food, or relay food from nurses to foragers. The proportion of ants engaged in foraging decreases with colony size because many ants in large colonies are not exposed to recruitment signals.