A nighttime hike through the Brazilian Amazon can bring any number of bizarre finds. But that didn’t blunt Leandro Moraes’s shock last November when he found a fist-sized moth sticking its tongue into a sleeping bird’s eyeball.
Moraes, a herpetologist for the National Institute of Amazonian Research, had been combing the banks of the Solimões River in northwestern Brazil for amphibians and reptiles when he shined his light on a Black-chinned Antbird. As it dozed on a low branch, Moraes noticed a big, brown moth, which he identified as Gorgone macarea, a type of tiger moth, clinging to its neck. From its perch the insect snaked its proboscis into the bird’s shut eyelid, seemingly to lap up any leaking tears.
Later that night around 1 a.m., Moraes came across another Black-chinned Antbird being probed by the same kind of tiger moth. Neither tear donor seemed bothered by the intrusion; they stayed still and kept on snoozing, Moraes writes in his report, published in The Scientific Naturalist last week. He’s one of the few people to document moth-on-bird “lachryphagy,” with previous accounts from Madagascar (2007) and Colombia (2015).
Now, before you start judging, consider the moth’s needs for a moment. The insects have fleeting adult lifespans that revolve around finding a mate, winning over that mate, and, at long last, mating to produce dozens of wriggly little angels. To up the chances of fulfilling their one earthly purpose, many species of male moths and butterflies engage in a behavior known as puddling: They drink copious amounts of salty liquids to create a nugget of NaCl called a nuptial gift. This engagement ring of sorts is stored beside the sperm so that when it comes time to sex it up, the female can snack on the salt—or save it for the future offspring.
In general, puddling takes place in natural or roadside pools. But some tropical moths and butterflies get their salty fix from mammal and reptile tears. Remember the caiman photographed with a Frida butterfly crown, or the thirst-trap turtles filmed along the Amazon?
Birds, on the other hand, are rarely observed as targets, maybe because a bulk of the activity happens at night and is overlooked. Or it could be that their tears are only harvested when other sources are scarce. In his write-up, Moraes mentions that tiger moths usually draw salt from sediment-filled floodwaters. When those waters recede, they need to find other places to puddle.
Antbirds, with their large eyes and gentle disposition, offer an easy, briny snack. Their tears might also hold essential proteins like albumin, which certain tiger moths are able to digest. It’s unlikely that the bird is getting anything in exchange, and so far all the witnesses have said the interaction seems harmless.
So, how widespread is this eye-juicing behavior? That’s still not clear, though previous accounts have involved different species of moths and birds. In Madagascar, for example, the culprit was an owlet moth that used its barbed tongue to hook onto a Common Newtonia’s cornea. (Owlet moths are smaller than tiger moths, which means their proboscis reach is limited and they have to sit on the host’s head.) In Colombia it was another tiger moth vamp-ing on a Ringed Kingfisher.
Just proves that birds really are the salt of the Earth.