In Brazil’s Pantanal wetlands, a Yacare caiman (Caiman yacare) pays no heed as an elegant Julia heliconian butterfly (Dryas iulia) alights on its toothy maw. What looks like a treacherous perch probably presents no great risk to the delicate insect. The caiman is likely just “gaping,” a common behavior in many reptiles—not unlike a dog panting—that enables them to regulate their internal body temperature. Besides, for this butterfly at this particular moment, one drive is significantly more powerful than wariness: the quest for life-sustaining salt.
Adult butterflies and moths use their elongated, tongue-like proboscis to suck up life-sustaining fluids. Energy-rich nectar is what most often comes to mind when we think of foraging butterflies and moths, but the insects also seek out sources of minerals and other nutrients critical to their reproductive success. In some environments—like the Pantanal, far from either South American coast—salt sources can be challenging to find. To supplement their diet, butterflies and moths native to these areas engage in a surprising behavior known as “tear-feeding,” or lachryphagy. Some go so far as to actively irritate their hosts’ eyes as a way of eliciting an extra tear or two.
Tear-feeding likely evolved from “puddling,” a behavior in which butterflies congregate around muddy pools to sip the mineral-rich water. Scientists think that by essentially puddling around the eyes of large reptiles and mammals, including humans, tear-feeding butterflies may find not only a critical source of sodium but extra protection from their own predators as they drink their fill.
Pantanal, Mato Groso, Brazil
Wim van den Heever
Wim van den Heever has been interested in both photography and nature for as long as he can remember. Raised in a family where photography was more a lifestyle than a hobby, he had many opportunities while growing up to visit Southern Africa's Game Parks. He now travels the world to capture images of extraordinary wildlife and natural phenomena, and hopes that his photos serve as a reminder not only of the beauty of nature itself, but also the threats it faces.
Katie Jewett is a Bay Area science writer, previously at the California Academy of Sciences and now at the Stanford Center for Ocean Solutions, where she loves learning something new about our planet every day. Previously, she spent winters in the Colorado Rockies and summers living and working on the water.