Variety in a Caterpillar’s Diet Could Spell Its Doom

There's an old saying: "You are what you eat." For caterpillars, taking on the characteristics of their food can be an issue of life or death.

A new study, published today in Proceedings of the National Academy of Sciences, shows that caterpillars who nosh on just one or two plant species—dietary specialists—are better able to hide from hungry birds than caterpillars who eat a variety of plants—dietary generalists.

Researchers from the University of California–Irvine and Wesleyan University sampled the eating habits of 41 forest caterpillar species in central Connecticut. The answer was in the leaves, so to speak: Specialists are more likely to blend in with their plant of choice than the unlucky generalists, whose ranging diets make consistent camouflage impossible. Avians then spot generalist larvae more easily—bad news for the bugs, but good news for damaged plants, which benefit from birds eating their unwanted pests.

Michael Singer of Wesleyan University, one of the study's lead authors, said these new insights could help explain why tropical forests tend to have so many specialists, especially among insects and other small organisms. "Tropical forests have a whole lot of predator diversity," he said. "Lots of different birds, ants, other predators." Pressure from all these predators could push their vulnerable prey to evolve into specialists, who design defenses around their diets or habitats of choice.

It's a complex ecology that might just boil down to the choice on how to chow down.