Colonies are small, with 100-200 workers and a single, singly-mated queen (Foitzik, Haberl, Gadau & Heinze 1997). If sufficient nest sites are available, a colony may fragment during spring and summer. Conversely, a shortage of nest sites can lead to the merging of unrelated colonies, generally with only one queen surviving the amalgamation (Foitzik & Heinze 1998). Although a newly-mated queen is capable of founding a colony on her own (Plateaux 1970), young mated queens may seek adoption by an established nest. In the latter case, the alien queen remains passive in the face of initial attack. Later she attacks the resident queen, workers and brood, and queen-queen aggression leads to the elimination of one of the queens (Stratz, Strehl & Heinze 2002). Workers can lay eggs which develop into males, but only start to do so if their colony loses its queen (Heinze, Puchinger & Hölldobler 1997).