Last December, passengers on a boat trip down Costa Rica‘s Puerto Viejo River were treated to a strange sight: a butterfly and a bee drinking the tears from a crocodile’s eyes.
The encounter between the insects, a Julia butterfly (Dryas iulia) and a bee (Centris sp.), and the spectacled caiman (Caiman crocodilus) lasted more than 15 minutes, as the reptile placidly permitted the insects to sip from its eyes as it basked on a log. (Also see “Crocodiles Really Shed Tears While Eating, Study Says.”)
Carlos de la Rosa, an aquatic ecologist and director of the La Selva Biological Station in San Pedro, Costa Rica, led the group and photographed the occurrence. He reported his observations in a peer-reviewed letter in the May edition of Frontiers in Ecology and the Environment.
The chance encounter yielded a remarkable photograph. It also raised questions about “tear-feeding,” a phenomenon otherwise known as lachryphagy, which has been well documented but remains poorly understood.
Why Feed on Tears?
A number of insect species including moths, butterflies, and bees are known to tear-feed, usually on mammals and in some cases even humans.
Tear-feeding on reptiles is less well documented, but in every case the insect seems to be in pursuit of nutrients and minerals—chiefly salt. (See more butterfly pictures.)
“Sodium and some of those other micronutrients are hard to find in nature,” said de la Rosa. “Butterflies and bees consume nectar, and nectar does not have a lot of salt. But they still need salt for egg production and for their metabolism.”
Watch a video of the incident in Costa Rica.
To scavenge the vital mineral, insects look for tears, sweat, feces, urine, and—among hematophagous insects like mosquitos—blood. Those that drink tears are referred to as “lacryphagous,” from lacrima, the Latin word for “tear.” (See “Mouse Tears Are Aphrodisiacs.”)
A similar, and better studied, insect behavior that seems to serve a similar purpose is called “mud-puddling.” Butterflies and other species that employ this strategy will congregate around and drink from puddles containing mineral deposits.
“You see the butterflies down on the [ground], and they drink water, usually to gain salt,” explained Jérôme Casas, an ecology professor at the University of Tours in France. “[The] salt [is] either used for biological purposes or it’s transmitted through the sperm as a gift to the female. So it’s really a valuable item.”
Benefits and Amenities
Whether tear-feeding behavior can be deemed symbiotic depends on your definition. Does symbiosis require mutualism, in which both animals benefit? Or merely a relationship between two organisms in which at least one benefits?
De la Rosa subscribes to the latter definition. While there’s no clear benefit to the animals providing the tears, he says, the behavior doesn’t seem to hurt them either. According to de la Rosa, some species are less bothered by tear-drinkers than others.
“From my few observations, the caimans don’t seem to be bothered at all by all this attention. The river turtles, however, are less tolerant to the bees buzzing close to their eyes. I’ve seen them shaking their heads at the bees and eventually even jumping back in the water.”
Casas speculates that crocodiles and turtles—along with large mammals like cows—are likely targeted by salt-seeking insects due to their placid nature. (See National Geographic’s pictures of alligators and crocodiles.)
“Crocodiles and turtles are very stationary,” he said. “When they sit somewhere, they sit for hours.”
De la Rosa estimates he’s seen the phenomenon at least four or five times in the past two years.
But, he says, it’s hard to quantify how common tear-feeding behavior really is, because it’s so ephemeral. And it would be harder still to reproduce such spontaneous interactions in a lab setting. Yet a wealth of photographic evidence suggests that the phenomenon could be fairly common.
In 2009, Casas and his colleague Olivier Dangles observed a bee drinking the tears of a yellow-spotted river turtle in Yasuní National Park, in the Ecuadorian Amazon. They documented their observations in Frontiers in Ecology and the Environment in 2012.
Casas says the phenomenon could help shed light on “the surprising world of insect-vertebrate interactions. We always think about mosquitos biting us, but there is way more than [that].”
A Closer Look
How important is such behavior to a given ecosystem?
“That’s one of the bigger questions,” said de la Rosa. “We don’t know how essential these relationships are to the survival of those species. It could be that it’s just an occasional, fortuitous, or opportunistic source of salt. Or it could be absolutely essential.”
To find the answer, de la Rosa and Casas both stressed the importance of traditional field research—without which such serendipitous observations wouldn’t be possible—in a world of increasingly computerized research methods.
“The scientific community has drifted very strongly toward high-tech types of studies [like] genomics,” said de la Rosa.
“And natural history itself, which is simple observations of events and phenomena in nature, has [been on the decline]. I’m all for technology, but it doesn’t replace the observations of phenomena in the field.”
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