Written by Raymond Nakamura
Once upon a time (before the Internet), Raymond earned his doctorate studying the hydrodynamics of sand dollars. Nowadays he rents his brain at raymondsbrain.com for writing, cartooning, and thinking, when he is not washing the dishes, walking the dog, or helping his daughter with homework. Follow him on Twitter @raymondsbrain.


Butterflies and other insects sip tears of crocodiles and other reptiles to gain salts

Created date

Thursday, May 10, 2018 - 2:16pm

Ever Wonder About Crocodile Tears?

To shed crocodile tears, is to show insincere remorse. This expression comes from the fact that crocodiles actually cry when they consume their victims. I had never really thought about the biological significance of this expression until I visited a butterfly garden in Costa Rica. We learned that certain butterflies actually drink crocodile tears, which made me wonder about both the butterfly and the crocodile tears!

Crocodile Tears

Crocodiles do indeed shed tears. These tears contain proteins and minerals. The tears help keep the eye clean and lubricate the nictitating membrane, the translucent extra eyelid found in many animals. Kurt Vliet, a biologist in Florida, observed the incidence of crying among lunching caimans and alligators that had been trained to feed on land at an alligator farm. The study began in response to a query from a neurologist dealing with a rare human disorder known as "Crocodile Tears Syndrome" in which sufferers shed tears while eating because of facial nerve damage. Vliet didn’t actually study crocodiles because they are too agile and aggressive, but caimans and alligators are close relatives. He only looked at seven animals, but of these, five were noted as crying while eating. I'm not judging the fact that he decided to not risk his life to collect more data, but I do think the subject could still use some more research!

The cause of tears in crocodilians is unclear. Apparently they hiss a lot while eating and so something to do with sinuses might be activating the tear glands. But they also shed tears just from being on land for a while, whether or not they are eating. I wondered whether it would be possible for the tears to help with water balance, but I have not been able to find anything on this. In any case, remorse, sincere or otherwise, does not seem a likely cause for crocodile tears, though again, the subject could benefit from more study.

Butterfly Behaviour

The butterfly the guide mentioned was the Julia butterfly (Dryas iulia). This bright orange butterfly is popular in butterfly gardens because it is long-lived and active throughout the day. Female Julia butterflies drink nectar, but the males, also called Julia, frequent wet places like mud puddles to acquire salts and minerals, which tend to be in limited quantities in the tropics. The males pass on these nutrients to the female during mating. Mud-puddling has been observed in various species of insects and various hosts. I think the reason the guide mentioned that particular butterfly was because an ecologist named Carlos de la Rosa, whos is based in Costa Rica, captured a Julia butterfly and a bee on video sipping at the eye of a spectacled caiman and he wrote a short paper on it. How important and prevalent tear-sipping is among butterflies and other insects is still unknown.

Originally, I thought the Julia butterfly was really weird for living off the tears of crocodiles. But now I see that they are an example of many insects doing similar things and that crocodile tears are just one bottle from a whole liquour cabinet of fluids containing the desired salts and nutrients. It's not as pithy but it makes more sense. Maybe shedding crocodile tears should mean something more like, "providing context for a story that is more complicated than you might have thought."

If you have any such crocodile tears to shed, by all means do so!

Add comment