Butterflies and bees have found an unlikely source of nutrients in the tears of crocodiles lazing on the banks of the Río Puerto Viejo in northeastern Costa Rica.

Aquatic ecologist Carlos de la Rosa spotted the phenomenon while passing the crocodiles on a boat travelling along the river.

De la Rosa photographed the insects drinking the tears of a spectacled caiman, with the insects fluttering around the predator as it basked in the sunshine.

Published in the journal Frontiers in Ecology and the Environment, de la Rosa, from the La Selva Biological Station for the Organisation for Tropical Field Studies in San Pedro, Costa Rica, said the sighting raised questions about why insects have chosen to find nutrient in this unusual place.

He notes that salt is often a rare and valuable resource on land, and that it is common to see butterflies sipping from mineral-rich mud puddles.

However, when minerals are rare in soil, animals can turn to less conventional places to find their nutrients, including sweat, tears, urine and blood.

Previously, butterflies and moths have been spotted in the Amazon feeding on the tears of turtles. However, this behaviour has only recently been observed and little research has been done in the area.

"I did a Google search for images and I found out that it is quite common! A lot of people have recorded butterflies, and some bees, doing this," he said.

Mr de la Rosa lives in the lowland rainforest, where just recently he spotted a new species of dragonfly on his way to breakfast.

"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."

"Those are the kinds of things that, you know, you don't plan for them, you can't plan for them. You just keep your eyes open and have curiosity, and when you see something that doesn't seem to fit, dig."