In the jungles of Ivory Coast, monkeys and chimps forage for food, sleep in trees and travel in groups. Not far behind follow primatologists, like Jan Gogarten, a postdoctoral researcher at the Robert Koch Institute in Germany.

Dr. Gogarten was spending a lot of time in the jungle tracking mangabey monkeys when his attention was drawn to another constant presence there.

“We had these flies always around,” he said. Dr. Gogarten wondered whether the clouds of these flies could travel long distances along with the primates, and whether they were carrying disease.

[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.]

Now he and his colleagues have reported, last month in the journal Molecular Ecology, that some flies stayed with a group of mangabeys in Tai National Park for up to 12 days and across significant distances. Some of these flies also tested positive for a bacterium responsible for many gruesome monkey and chimp deaths over the last few decades in the park.