The wood‐feeding cockroach Cryptocercus is usually believed to live in aggregations. Field observations, however, gave evidence for the existence of distinct family groups living in different gallery systems. This study investigates intraspecific behavioural interactions with respect to the social structure. The interactions among family members were observed in artificial burrows in the laboratory. Individuals from different families were brought together experimentally and the resulting alarm and fighting behaviour was studied. The importance of Cryptocercus for the evolution of termite sociality is discussed.