Credit: S. DOBATA

Proc. R. Soc. B doi:10.1098/rspb.2008.1215 (2008)

The ant Pristomyrmex punctatus has no queens — female workers reproduce asexually. But that doesn't mean that everyone is equal. Some nests harbour 'cheaters' that shirk their duties and concentrate on reproduction.

Shigeto Dobata of the University of Tokyo and his colleagues found that there are two morphologically distinct types of P. punctatus worker. One does the work; the other, which is larger (pictured, right) and has more ovarioles, does hardly anything except lay eggs.

Genetic tests showed that cheaters, although closely related to their nest-mates, are genetically distinct. They also revealed the same cheater lineage in more than one nest, suggesting that it can spread between colonies, and leading the researchers to describe the cheats as a transmissible 'social cancer' that has evolved to exploit the cooperative behaviour of the majority.