SWARM SIZE AND EFFICIENCY. “Groups of robots using ant-inspired algorithms of decentralized control techniques foraged more efficiently and maintained higher levels of group energy than single robots. But the benefits of group living decreased in larger groups, most probably because of interference during foraging. Intriguingly, a similar relationship between group size and efficiency has been documented in social insects.”
http://www.nature.com/nature/journal/v406/n6799/full/406992a0.html