Monarch caterpillars are beating each other up over food

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Monarch caterpillar snacking on leaf
Photo: Sarah8000 (Getty Images)

Dark stuff happens when you’re hangry. Best-case scenario, you snap at a loved one before you can get your hands on a Snickers. Worst-case scenario, you head-butt your peers into oblivion over a milkweed leaf. According to Science News, the latter is a relatively common smackdown strategy among monarch caterpillars as they grapple with a dwindling food supply. It’s rough out there on the larval scene.

According to Science News, researchers have witnessed roaming caterpillars head-butting and lunging at their caterpillar compatriots in an attempt to commandeer milkweed leaves. It’s apparently a tactic to score a beefier leaf in a time when climate change is killing off milkweed, the monarch caterpillars’ sole food source. Crawling from plant to plant takes energy, so if a caterpillar lands on a leaf that’s already, er, occupied, they might not get enough food to grow. Enter the larval smackdown. Science News also cites Elizabeth Brown, a biologist involved in the study. Brown explains that the victimized caterpillar often exhibits a “loser response,” which involves leaving the contested area entirely whether or not a stream of smack talk emerges from the caterpillars’ tiny mouths.

Turns out, other types of caterpillars have shown similar aggressive behavior. The big question: do aggressive caterpillars grow into aggressive butterflies? Is caterpillar aggression a troubling evolutionary trend? Can humankind expect a Hitchcockian butterfly onslaught in the next 10 to 20 years? The answers remain unclear—but I, for one, will be stocking up on butterfly nets. And milkweed.