Tom Turpin
Professor of
Purdue University


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Unusual caterpillar walks on the wild side

pinkish underside of Ilia underwing caterpillar
Ilia underwing caterpillar
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Last Monday morning a caterpillar was discovered crawling along the first-floor hallway outside my office. It was brown in color, a little over an inch in length and seemed to be in a hurry to get somewhere. At least it was until an alert graduate student imprisoned it in a petri dish.

Exactly how this particular caterpillar found its way into Smith Hall at Purdue University is a mystery. Truth be told, a caterpillar showing up in Smith Hall is a somewhat-regular occurrence. You see, Smith Hall is home to the Purdue Department of Entomology.

Any university academic unit with entomology in the name is likely to have a few caterpillars in residence. Such caterpillars are technically research animals. One common research caterpillar is the tomato hornworm. That well-known pest of our gardens has become an insect equivalent of the lab rat for research purposes.

Caterpillars in natural habitats and their laboratory counterparts need food. The laboratory caterpillars could be chowing down on plants or on some artificial food concoction especially blended to meet their nutritional needs. On occasion these pampered pet caterpillars will break out of their laboratory homes and make a run for it.

But this surprise visitor to Smith Hall was not truant from our hornworm rearing facility. For one thing it was the wrong color - the laboratory hornworms are a blue green. For another the caterpillar's behavior was unusual. When disturbed the brown caterpillar would flip over on its back and expose a pink-colored underside.

When the brown-turned-pink caterpillar was on its back it would thrash violently from end to end. What we had here was an insect displaying a flash-coloration behavior that is useful to ward off predators.

Here's how it works. A brown-colored insect would blend into the environment, such as the bark of a tree, and generally go unnoticed by potential predators. If discovered, the insect flashes - exposes a bright color pattern - that will startle the predator.

The pink-bellied caterpillar turned out to be the immature of a moth known as an underwing. The underwing moths get their name from the fact that the hind wings of some species are brightly colored, often with orange or red and black-and-white markings. The outer wings are generally dull colored and conceal the back wings when the insect is at rest. So, in this case, both the caterpillar and the adult moth exhibit flash coloration as a useful tool to ward off predators.

moth with pink underwings
Ilia underwing moth
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This particular insect has the scientific name Catocala ilia. Pieter Cramer, a Dutch merchant and entomologist, named the moth in 1776. The genus name Catocala is based on "kato," meaning behind, and "cala," the Greek word for beauty, in reference to the beautiful hind wings. The species name of iliais from the goddess of Roman legend of that name.

Apparently Cramer followed the lead of Linnaeus to name Catocala moths, also called the underwing moths, after specific women or females in general. So the ilia underwing that invaded Smith Hall is also known as the beloved underwing or the wife underwing. We also find Catocala moths known as the bride, the little bride, the newly wed, the darling, the nymph, the little nymph, the Delilah and the Desdemona underwings.

The Catocala moths are found throughout the world, but a high percentage of named species and some of the most beautiful come from North America. So it is not surprising that an ilia underwing caterpillar showed up "right here in River City." But why was it in the hall of a building? The best guess is that the caterpillar had hatched after spending the winter in the egg stage. It had fed on an oak tree and had descended to the ground to crawl into the soil and somehow wandered into the building.

So there it was minding its own business searching for a pupation site when the graduate student discovered it. The caterpillar tried to scare the student away using the old flash-the-bright-colors approach. It didn't work. But what can you expect when you decide to take a walk on the wild side?


Writer: Tom Turpin
Editor: Olivia Maddox