Monarch caterpillars head-butt each other to fight for scarce food

When food and space get scarce, competition can bring out the worst in monarch caterpillars. In the laboratory, researchers watched as roaming caterpillars looking for a hard-to-find meal started head-butting and lunging at fellow caterpillars munching on a milkweed leaf. That aggressive behavior is apparently meant to disrupt the feeding insects and help the instigators […]