When animals cry, tear-drinking organisms hop up to the "bar" to quench their thirst, new research finds.
Tears are sort of like sports drinks, in that they contain various vitamins and minerals in a liquid solution. (They also contain mucus, antibiotics and oils, which is probably why entrepreneurs aren't bottling human tears for sale.)
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But, for tear-drinking species like butterflies and bees, tears are refreshing goodness. Aquatic ecologist Carlos de la Rosa and his team watched and photographed bees and butterflies drinking crocodile tears. A paper on the discovery is published in the latest issue of Ecology and the Environment.
The croc, a spectacled caiman, seemed not to mind. It was relaxing on the banks of the Río Puerto Viejo in northeastern Costa Rica when the drink fest happened.
"It was one of those natural history moments that you long to see up close," de la Rosa, director of the La Selva Biological Station for the Organization for Tropical Field Studies in San Pedro, Costa Rica, said in a press release. "But then the question becomes, what's going on in here? Why are these insects tapping into this resource?"
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He'd previously seen butterflies and moths in the Amazon feeding on the tears of turtles and other caimans. Other researchers have witnessed bees sipping tears.
A clue helping to explain why this happens comes from puddles.
Butterflies often flutter around mud puddles, sipping their mineral-laden water. Though bountiful in the ocean, salt is often a rare and valuable resource on land. We obviously get more than our fair share in salty foods, but butterflies and other insects need to look for other sources.
In fact, de la Rosa said that when minerals are rare in the soil, certain insects and other animals can acquire salt and minerals from sweat, urine and even blood. When given those options, tear sipping seems easier and more palatable!
Tear drinkers can target humans too. In parts of Thailand, where people spend a lot of time outdoors and where minerals can be rare in local soils, bees have been known to sip human tears. It's therefore not implausible that when our prehistoric ancestors stubbed their toes or got depressed, smaller species would come around to clean up their tears. Nature is a wonderful recycler.
As for de la Rosa, he was thrilled to capture tear drinking in the moment. Some of the best discoveries are unplanned and simply occur when a person is in the right place at the right time, but is also prepared.
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"I learned I have to carry a camera with me 24/7, because you never know what you're going to find when you're walking to the office or the dining hall," he said.
One day, for example, he spied a new species of dragonfly on his way to breakfast. The dragonfly had emerged from its larval form in the small pool of water caught in the cupped leaves of a bromeliad plant. De la Rosa did a double take. Dragonflies don't live on bromeliads. Or do they?
"Those are the kinds of things that, you know, you don't plan for them, you can't plan for them," he said, adding that there was only one known species of dragonfly in the world that lives in bromeliads and now there will be two.
"You just keep your eyes open and have curiosity, and when you see something that doesn't seem to fit, dig."
Photo: A Julia butterfly and a solitary bee sip tears from the eyes of spectacled caiman on Costa Rica's Puerto Viejo River. Credit: Carlos de la Rosa