On a humid afternoon a few years ago in the Peruvian Amazon, a flicker of motion caught Phil Torres' eye. A cherry-spot metalmark butterfly (Adelotypa annulifera) was drinking nectar from the tips of bamboo shoots.

As he watched, he realized something strange was going on. Normally butterflies only sip at nectar for a few seconds, minutes at most—but these butterflies were feeding for hours, Torres later discovered. 

Even more bizarre, ants that live on the bamboo and chase away other insects from their home ignored the butterflies. (See "Scientists Uncover Strange Secret Life of a Jungle Butterfly.")

Many animals steal food, but this is the first time that scientists have discovered adult butterflies swiping food from ants.

“It was really cool. I had never seen anything like it,” says Torres, co-author of a new study on the behavior in the Journal of the Lepidopterists' Society.

Biologists already knew that metalmark larvae produce a nutritious