Detailed observation of 60 individually labelled young workers of the ponerine ant Ectatomma tuberculatum during the first 45 days after emergence indicated that behavioural specializations appear progressively according to an individual's age. A comparison of control ants and isolated young workers, deprived of early social contact for a fixed interval at different post-emergence ages, revealed the existence of a sensitive period during which social stimuli affect the establishment of behaviour related to brood care. This sensitive period may involve two phases: a 'permissive' period, during the first 2 days of social contact, and a 'stabilization' period, during the subsequent 2 days. Inglés