Insects go to the caiman eyelids for a tearful meal

We say “crocodile tears” to imply someone’s emotion is fake. But for insects, salty tears can have genuine value, and are even worth approaching a reptile to reap.

In December 2013, Dr Carlos de la Rosa and colleagues spotted a spectacled caiman (Caiman crocodilus) basking beside the Puerto Viejo River in Costa Rica. On closer inspection, the reptile had a Julia butterfly near one eye and a bee at the other, and the insects appeared to be "drinking" the caiman's tears.

“There are observations of similar behaviours for the Amazon basin and other South American locations,” says de la Rosa, who directs the nearby La Selva Biological Station. “[But] being a simple observation of a fairly rare event, the record is important, especially for Costa Rica. I am now more aware of these interactions, and have observed them again, on river turtles here.”

The insects are probably sucking up valuable nutrients from the tears. “While sodium is an essential element for the metabolism and reproduction of these insects, there are also proteins, enzymes and micronutrients that could also play a role in the fitness of the insects tapping this resource.”

What's in it for the caiman is less obvious. This one seemed very tolerant of the butterfly and bee, according to De la Rosa, who reported the observation in Frontiers in Ecology and the Environment. "However, I've seen these bees approach river turtles, and the turtles are not as tolerant or pleased, shaking their heads and even jumping back. We don't know what if any benefits are received by the caimans."