Researchers have found a variety of commensal relationships between different species of animals - some stranger than others. One of the most surprising ones is certain animals' practice of drinking other animals' tears. A new study, published last week in Ecology and also reported in Science Magazine features a rare documentation of a moth drinking the tears of a sleeping bird.
The video was filmed by the ecologist Leandro Moraes of the National Institute of Amazonian Research in Manaus, Brazil, in November 2017. Moraes was on a research expedition in the heart of the Amazon when he noticed a strange phenomenon: a black-chinned antbird (Hypocnemoides melanopogon) resting on a branch with a erebid moth (Gorgone macarea) attached to the back of its neck. The moth sent an antenna into the eye of the sleeping bird and can be seen drinking from it. Three quarters of an hour later, Moraes found another moth drinking from the eye of another sleeping bird.
Researchers know that different species of insects often drink the tears of larger animals. According to one theory, salt water provides minerals and proteins that are not present in running water. To this day, researchers have found that butterflies tend to drink crocodile tears as they rest in the sun by the river. Some bees are known for drinking the tears of turtles. In both cases, however, the tears belong to slow moving animals that do not see the insect as a source of food. That's why the new discovery is surprising: fast-moving birds do not seem to be the ideal candidates for thirsty moths. But as Moraes discovered, the cautious moths take advantage of the birds' slumber to carefully drink their tears using their proboscis and from a safe distance.