When we see leaf-eating insects green, and bark-feeders mottled grey, the alpine ptarmigan white in winter, the red-grouse the colour of heather, and the black-grouse that of peaty earth, we must believe that these tints are of service to these birds and insects in preserving them from danger.

~Charles Darwin

Yesterday, while working in the yard, I stumbled across an unusual caterpillar just beneath the surface of my mulch pile. Two things about it jumped out at me – first, it was pretty large compared to most caterpillars so early in the year, and second, its colors were so striking. And then, to add another, when I picked it up, it jumped and thrashed from side to side.

Ilia Underwing larva (click photos to enlarge)

I remember seeing a picture of this species in my caterpillar bible (Caterpillars of Eastern North America, by David L. Wagner) but this was the first one I have encountered. After identifying it as an Ilia Underwing, Catocala ilia, I discovered it is actually one of the most common of the underwing moth species in the East. How have I missed seeing one all these years? Then I read that there is only one generation per year and mature caterpillars are most often seen in early spring. To be honest, over the years I admit to doing more of my caterpillar searches later in the season, when some of our more showy species reach their full size. Look what I have been missing! Sources say that the eggs are laid in the fall and hatch in early spring. The larvae feed primarily on oak leaves. Perhaps my find was burying down into the mulch getting ready to pupate.

Ilia Underwing larva showing a glimpse of the rosy underside

The dorsal surface can be gray or brown, or, as in this case, a mottled color that is a great mimic of a lichen-covered twig. One thing they have in common is a noticeable rosy color to their ventral surface (this guy did not like to be handled so here is just a glimpse of its rosy underside).

Ilia Underwing larva blending with a lichen-covered branch

I brought the larva inside with a couple oi twigs I found laying nearby and photographed it. When I nudged it onto a twig, it would thrash, and then crawl a short distance and assume the position. When on a bare twig, it clings tightly but is visible (perhaps the gray or brownish larva blend in better on bare twigs). But when it crawled onto the lichen-covered branch, I could see how this caterpillar can literally disappear before your eyes (or perhaps those of a hungry bird).

The color patterns and textures of this larva are a great lichen mimic

It is always a treat to discover something new and learn how it lives its life just outside my window…all I need to do is get outside and look to once again be in awe.