In November 2017, ecologist Leandro Moraes of the National Institute of Amazonian Research in Manaus, Brazil, was in the middle of a research expedition in central Amazonia when he spotted something strange: a black-chinned antbird (Hypocnemoides melanopogon) resting on a branch with an erebid moth (Gorgone macarea) on the back of its neck. The moth was probing one of the bird’s eyes with its proboscis and appeared to be drinking from it. About 45 minutes later, Moraes came across a different moth drinking from the eye of another resting antbird.
Butterflies and bees also drink the eye secretions of other animals—butterflies are partial to basking crocodiles, whereas bees like turtle tears. But fast-moving birds are unlikely hosts for these insects. At night though, the metabolism of birds drops; that’s when nocturnal moths exploit their tears, Moraes speculates.
The moths probably acquire nutrients such as sodium and proteins from eye secretions of these birds, Moraes reports this week in Ecology. By sitting still on a resting bird’s back and using their long proboscis to reach its eyes, they avoid disturbing the bird, all the while maintaining a safe distance.