This behavior by the fluttering insects was so unusual that scientists had to invent a new word to describe it.

by Annie Roth via The New York Times

Butterflies seem gentle as they flutter from plant to plant. But some may be more murderous than you imagine. Naturalists recently witnessed several species of milkweed butterfly harassing, subduing and subsequently feeding on milkweed caterpillars, presumably to get their fill of toxic alkaloids inside the larvae.

This behavior was described in an article published Wednesday in the journal Ecology. The authors of the paper say they are unaware of similar behavior being documented among other butterflies, or any insects for that matter, that are so closely related. Although butterflies had previously been observed feeding on grasshoppers that harbor toxic alkaloids, no one had ever documented adult butterflies stealing such compounds from their own kin.

Scientists did not have a word to describe this toxic behavior, so the study’s authors came up with one: kleptopharmacophagy.

The discovery was made in December 2019 when two friends traveled to the Tangkoko Batuangus Nature Reserve on the northern part of Indonesia’s Sulawesi island. Yi-Kai Tea, a graduate student studying ichthyology at the University of Sydney and the Australian Museum Research Institute, and Jonathan Wei Soong, a naturalist from Singapore, share a passion for macro-photography and butterflies and had decided to spend their holiday photographing the reserve’s stunning array of fluttering insects.

Mr. Tea and Mr. Soong spent hours photographing the insects. It wasn’t until the end of the day, when they were going over their pictures, that the two men realized they had documented strange and sinister behavior.

After making the initial observation, Mr. Tea and Mr. Soong spent the next two days at the site doing their best to document the gruesome gorging in greater detail.

“We thought it was really cool,” Mr. Soong said, adding that he finds milkweed butterflies “kind of metal.”

Mr. Soong and Mr. Tea spent hours watching seven different species of milkweed butterfly, including Blanchard’s ghost and the ismare tiger butterfly, scratching caterpillars, both dead and alive, so violently with mighty claws on their feet that the caterpillars’ internal juices oozed out. They said the behavior can’t be described as predatory because many caterpillars survive the encounters.

Read the full article here (including photos of the behavior).

Photos above: Blanchard’s ghosts, Idea blanchardii by mehd and ismare tiger, Danaus fulvus by gancw1