Proc. Natl Acad. Sci. USA 106, 17452–17456 (2009)

Many insect species organize themselves into social classes with distinct roles, such as reproductive queens and sterile workers. How this 'eusociality' evolved is an open question.

Barbara Thorne at the University of Maryland, College Park, and her colleagues staged encounters between 25 pairs of colonies of dampwood termites (Zootermopsis nevadensis). During encounters, at least one colony in each pair lost its king or queen and the pairs merged.

The team found that worker termites developed into reproductive ones in 17 of the 25 merged colonies and that interbreeding occurred in 14 colonies. This shows that, in dampwood termites, which are similar to ancestral termites, workers can become breeders and inherit a colony and its resources, providing them with an incentive to stay with their colony and cooperate with non-relatives — a key aspect of eusociality.