Tom Turpin
Professor of
Purdue University







Caterpillars Sometimes Dress to Send a Message

In 1727, John Gay declared, "And what's a butterfly? At best he's but a caterpillar dressed." Gay put into words what humankind had for centuries recognized, that creeping caterpillars turned into winged butterflies. Through the miracle of insect metamorphosis, ugly caterpillars become beautiful butterflies.

It's a makeover story line suitable for the best, or worst depending on your perspective, of reality TV. It is a drama of nature that features greed, deception, murder and sibling rivalry. And it happens daily throughout the summer and fall in all kinds of environments.

Ugly might describe the unfolding drama, but it is probably unfair to categorize all caterpillars in such a way. After all, what is beauty or ugly is sometimes in the eyes of the beholder. I would suggest that caterpillars are not ugly, just very different from humans. On the other hand, not all butterflies are the paragon of beauty that some people associate with the name. But that is another story.

The metamorphosis of butterflies is what is described as complete. Complete metamorphosis means that the insect goes through four stages: egg, larva, pupa and adult. In complete metamorphosis, the larva does not look like the adult that it becomes. So the butterfly larva, called a caterpillar, does not look anything like the winged adult. Knowing the identity of a butterfly is no help in identifying the caterpillar.

So what do butterfly caterpillars look like, and where do you find them? Since butterfly caterpillars feed on plants, the best way to find caterpillars is to know the plants on which they feed and start looking there. For instance, the caterpillars of monarch butterflies will be found on milkweed plants.

Once a food plant is identified, it is helpful to look for signs indicating the presence of a caterpillar. These signs include holes in the leaves or the presence of insect manure. After all, what goes in must come out. Insect manure is called frass and can be seen accumulating on the ground or in the axils of the leaves of the food plant as the caterpillar goes about its daily life.

Some of the most conspicuous of the butterfly caterpillars belong to the swallowtails. Most of these caterpillars are smooth and brightly colored. The caterpillar of the black swallowtail can commonly be found in gardens, feeding on carrots, dill and parsley. The swallowtail caterpillars are generally green with black stripes and, sometimes, orange markings.

Caterpillars of the swallowtails, including the common black swallowtail, have a fleshy retractable organ above the head, which is used to release a pungent odor to help repel predators. When touched, the caterpillar will stick out the forked organ, much as a snake sticks out its tongue. A few of the swallowtail caterpillars have spots to resemble eyes of snakes. Most swallowtail caterpillars have white spots on their bodies when smaller to make them resemble bird droppings. They are just doing what it takes to not become a meal before having the chance to change into a butterfly.

The yellow and white butterflies are very common. Caterpillars of this group of butterflies are generally green in color. Such coloration is known as cryptic color and allows the caterpillar to blend in with its food plant. Caterpillars of the yellow butterflies generally have a white stripe along the side of the body. Some of these caterpillars have the habit of wiggling violently when disturbed. A few even drop from the plant on a fine thread of silk. Both activities help the insect avoid a predator.

Skipper butterfly caterpillars have smooth bodies with relatively large heads, which are more obvious than in most other caterpillars. Almost all of these caterpillars conceal themselves in leaves that are folded over.

The bushfoot, fritillary and checkerspot butterfly caterpillars have branching spines on their bodies. These spines help prevent caterpillars from becoming a meal for hungry insect predators.

The more one looks at caterpillars, the more it becomes obvious that they are dressed for success. And success is measured in living long enough to complete the caterpillar life cycle. So maybe for caterpillars, ugly is what ugly does!


Writer: Tom Turpin
Editor: Olivia Maddox