Capuchin monkeys often rub their bodies with a certain type of millipede  Laboratory tests show that secretions from the bodies of these millipedes are rich in two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate capuchins
Some scientists hypothesize that the monkeys rub their bodies with the millipedes because doing so helps protect them from mosquitoes
The capuchins rarely rub their bodies with the millipedes except during the rainy season, when mosquito populations are at their peak.