Some Moths Come to Drink Tears

A moth lands on the neck of a sleeping bird. It walks toward the head, uncoils a narrow proboscis and slips the tip beneath a closed eyelid. Then it drinks.

This is not a miniature horror invented for a nature documentary. It is lachryphagy: feeding on tears. A scattered assortment of moths has been observed taking eye secretions from animals including cattle, horses, deer, elephants, crocodilians and, in a particularly intimate variation, sleeping birds.

The behavior sounds extravagantly strange until tears are treated as chemistry rather than emotion. Adult moths live mostly on liquids, but sugary flower nectar and fruit juice do not provide everything an insect needs. Tears offer water, salts and small amounts of protein. Sodium is especially valuable to plant-eating animals because plants generally contain relatively little of it.

This is the same nutritional problem behind the more familiar sight of butterflies gathering on mud, dung or sweaty skin. Biologists call that behavior puddling. A tear-drinking moth has found a livelier mineral spring, one that blinks.

There is no single tear-drinking branch of the moth family tree. A 2013 review of moths and butterflies that consume blood, sweat and tears found the habits distributed among several lineages. The equipment varies with the method. Some species sip fluid already exposed around an eye; others use a probing proboscis whose ridges, hooks or movements may irritate the tissue and encourage more tears.

That distinction matters. A drinking straw is passive. A tear-feeding proboscis can be both straw and tiny rake. A major review of butterfly and moth mouthparts notes that the probing movements of some species increase tear flow and can cause pain when the host is human. The meal may manufacture a little more of itself.

The most startling specialists belong to the African genus Hemiceratoides. In western Madagascar, researchers observed H. hieroglyphica visiting two species of sleeping birds. The moth sat on the bird's neck and reached forward, inserting a sharply tipped, armored proboscis between the protective membranes of the closed eye. The original report, published in 2007, was the first scientific description of a moth exploiting tears from the closed eyes of sleeping birds.

The birds did not always remain serene. They shook their heads, scratched and tried to dislodge the insects. Yet the moths returned, sometimes staying at an eye for more than half an hour. The researchers argued that this was not a thirsty insect making an accidental stop: the visits were repeated, directed and supported by specialized anatomy.

For years, the behavior looked like one of Madagascar's evolutionary peculiarities. The island has no native elephants or hoofed mammals, the large and relatively tolerant hosts commonly visited by eye-frequenting moths elsewhere. Perhaps, researchers proposed, local moths had turned to birds because the usual mammalian faces were missing.

Then a sleeping bird in Tanzania complicated the story. Video showed another Hemiceratoides moth bothering a common whitethroat on the African mainland, where large mammals are hardly absent. A 2024 taxonomic study used that footage, museum specimens, anatomy and DNA to revise the genus and describe two new species. The authors concluded that bird tear-drinking may be a basic feature of the group rather than an island workaround.

The specialization is written into the moth's face. Hemiceratoides species have unusual modifications at the tip of the proboscis. In at least one species, males also carry long, fang-like mouthpart structures that researchers suspect help with feeding. What the fangs actually do, and whether females drink tears too, remain open questions.

So does the precise value of the meal. Salts are an obvious prize, but tears contain more than salt water. Earlier work found white blood cells being digested in the guts of some eye-frequenting moths, suggesting that protein can matter as well. The 2024 researchers asked whether the barbs of Hemiceratoides might irritate the conjunctiva to release more fluid. They did not claim to know.

That restraint is useful because spectacular animal behavior attracts tidy explanations faster than evidence. Even the word "tear" encourages a sentimental mistake. The moth is not drinking sadness. It is exploiting a physiological fluid, and the host is not volunteering it. Scientists have raised the possibility that eye-visiting moths could move microbes between animals, but the disease risk remains much less settled than the feeding itself.

Nor is every moth near an eye necessarily drinking. Researchers distinguish true lachryphagy from the broader habit of frequenting eyes. Proof can require close observation, specimens and mouthparts adapted to the task. A single eerie photograph may capture contact without revealing what, if anything, entered the insect.

Still, the confirmed cases are intimate enough. An eye must stay wet to work, which means the body continually maintains a thin exposed resource at its surface. Most creatures experience that film as protection. A tear-drinking moth experiences it as habitat: a saline margin where one animal's maintenance becomes another animal's meal.