Kibale fly-primate associations. Widespread fly-primate associations: larger monkey groups harbor higher fly densities

Flies are implicated in carrying and mechanically transmitting many primate pathogens. We investigated how fly associations vary across six monkey species (Cercopithecus ascanius, Cercopithecus mitis, Colobus guereza, Lophocebus albigena, Papio anubis, and Piliocolobus tephrosceles) and whether monkey group size impacts fly densities. Fly densities were generally higher inside groups than outside them, and larger groups harbored more flies. This pattern was strongest for colobine monkeys, who had smaller home ranges than the other primates studied here, suggesting that day range patterns may influence fly-primate associations. Fly associations increase with group sizes and could thus represent a cost to sociality.