Cheeky butterflies steal precious chemicals from young congeners

Researchers have not seen it before, but have already coined a catchy term for it: kleptopharmacophagy.

Butterflies seem like such lovely, fluttering creatures. But a new study has shown that some can also be quite homicidal. For the first time, researchers have spotted monarch butterflies feeding on live caterpillars — the young of their own kind.

A caterpillar is – as you probably know – the larva of a butterfly. Their menu consists mainly of poisonous plants. The chemicals that build up in their bodies as a result are used by the caterpillars for self-defense. While this “poison” doesn’t seem to affect the caterpillar that much, the chemicals can be very distasteful and even harmful to predators such as birds. Later, when the caterpillar has transformed into a butterfly, the poisons eaten together are reflected in the bright, warning colors on the wings.

Chemicals

But that’s not all. These chemicals also help male butterflies produce pheromones (sex odorants). During courtship, these act as a kind of ‘wedding gift’ for the females. Some of the chemicals are in their bodies, although male butterflies sometimes replenish their supplies by extracting it from plants. But in the forests of the Indonesian province of North Sulawesi, it seems that butterflies get these chemicals in a different, rather cruel way.

To steal

Instead of getting the chemicals from plants, male butterflies seem to have a macabre fondness for caterpillars. In their quest for the ultimate love drug, they harass living, dead and dying caterpillars belonging to the same subfamily. Then the cheeky butterflies steal the precious chemicals from these young congeners.

Cheeky monarch butterflies that prey on caterpillars. Image: Tea et. already.

Normally, the butterflies scratch open a chemical-containing plant with their sharp claws and then suck out the sap with their long, curled tongues. But now it appears that some butterflies also ‘scrat open’ live caterpillars. “Caterpillars are essentially just living leaves; they contain the same chemicals that the butterflies are looking for,” explains researcher Yi-Kai Tea. “Adult butterflies can therefore see them as an alternative source.”

Witness

The researcher witnessed this cannibalistic, “vampire” behavior while investigating North Sulawesi with his team. To his great surprise, he saw butterflies scratching leaves as well as living and dead caterpillars, and then sucking out the juices. “The caterpillars were still twisting their bodies in what seemed like a futile last-ditch effort to scare the butterflies,” Tea recalls. “This is the first time we’ve seen this behavior. We’ve called it kleptopharmacophagy, which means ‘theft of chemicals for consumption’.”

While monarch butterflies are known to sometimes literally go over corpses to obtain precious chemicals (for example, they also suck it out of the carcasses of other insects), this is the first time researchers have discovered they’re even targeting congeners. And their own larvae. “These simple observations raise questions about the ecology of these well-known butterflies,” Tea says. “For example, which exact connections are these butterflies particularly interested in? And are butterflies in other parts of the world also guilty of the same behavior?” The researcher hopes that future research will clarify things.