Imagine if you were a bird looking for some lunch. A caterpillar would do perfectly, so you poke around under leaves. Suddenly you see two large eyes. Will you eat it … or will it eat you? Caterpillars that have markings that look like snakes will startle bird predators, so they are often avoided—and not eaten. Sometimes it’s not the caterpillar, but the chrysalis that it makes when transforming into a butterfly, that wears the disguise. Such is the case for the species Dynastar darius darius of Trinidad, whose chrysalis form looks like the head of a pit viper snake. It even rocks back and forth, as if the snake is lunging forward.
A lot of caterpillars and pupae have false eye color patterns and snake-shaped heads (check this one out). Biologists identified hundreds of caterpillar species with false eyes and faces in a tropical forest in Costa Rica. Besides snakes, false faces may also look like lizards, birds and mammals. The markings do not look exactly like any particular species of animal, but when quickly seen, they look enough like predators to cause fear.
While they can look quite convincing, false eyes did not evolve from real caterpillar eyes. They evolved from circular structures on the caterpillar, like breathing holes, called spiracles. False eyes can be on the head or rear end of caterpillars, and on the front end of pupae.
Caterpillars hidden in a rolled leaf will poke their scary “face” toward the opening in the leaf when disturbed. Sometimes, false eyes are hidden in body folds, and pop out when the caterpillar reacts to being touched.
Since there are so many different types of caterpillars and pupae that use this scare tactic successfully, scientists believe that birds must be reacting on instinct when they move away from one of these caterpillars. For the bird, it’s better to err on the side of caution and avoid things that look like predators, even if it means mistakenly turning down a delicious meal now and then.