On a sugarcane leaf in northern India, a Pyrilla planthopper nymph hosts unwelcome guests: Atop its back a large pompom-like caterpillar of the moth Epiricania melanoleuca parasitically sucks the planthopper's body fluids; smaller, younger larvae of the same caterpillar species feed near the planthopper's head and above its hind leg. These caterpillars do not kill their hosts but weaken them to the point that they can't reproduce. That's good news for the cane industry: Pyrilla suck out cane sap and damage crops. In Uttar Pradesh, India, Epiricania melanoleuca caterpillars have been deliberately introduced into cane fields—an effective biological control against planthopper pests.