Am. J. Primatol. doi:10.1002/ajp.20601 (2008)

Many researchers would expect parasitic infection rates to increase as groups of animals get bigger and more hosts are available. Contrary to this, researchers reveal that as groups of red colobus monkeys (Procolobus rufomitratus) get larger, they have fewer parasites.

Tamaini Snaith at McGill University in Montreal, Canada, and her colleagues made the discovery while studying the monkeys in Uganda. They tested faeces for parasites and monitored group dynamics. The researchers noticed that large groups tended to spread out more than smaller ones, and suggest that this could lower infection rates.

They add that although the monkeys may be spreading out in response to the parasites, feeding competition could also be driving the spread, making the parasite reduction a happy accident.