Last month we explored some of the complexities related to a familiar example of mimicry between two of our butterfly species (viceroys and monarchs). It turns out that Vermont is loaded with amazing examples of mimicry. We just don't notice most of them. But then, that's the whole point.    

 

The photo from a friend in Maine.

This morning, a friend in Maine sent me a photo of a caterpillar he found on an oak leaf. The photo shows a blotchy brown, tan, and green, inch-long critter with a spiny projection a few segments behind the head. After digging a bit, I found that it's the larva of a dullish moth called a white-streaked prominent.  The larva eats oak leaves, mostly, and has a pretty neat skill set.   

 

The little bugger chews off some of the edge of an oak leaf and then, when it's not eating, squeezes its body into the damage it has done to the leaf. A photo of this in a book shows a damaged leaf of brown and green with a couple of veins sticking out. Surprise! One half of the image is a damaged leaf, and the other half is a leaf-damaging caterpillar. For me, at least, it is not possible to say where the plant ends and the animal begins.

What is all this craziness about? Caterpillars have two very different kinds of predators up here: well-sighted birds, and wasps that locate their prey by odor. The caterpillars' coloration, vein-like projection, and hiding-in-plain-site behavior is aimed at the birds. The bug feeds at night when the birds are sleeping. During the day, the birds hunt for something that is motionless and nearly invisible. (This assumes that birds see what we do.)

Lace-capped caterpillar, aka white-streaked prominent moth (Oligocentria lignicolor). Photo by swampthings.blogspot.com

We are left with the other important caterpillar predator, the wasps. I'm not talking here about hornets, which act like birds and just carry the unlucky insect home to the brood. Instead, I refer to parasitoid wasps, which few of us ever see. These are usually smallish wasps that search for caterpillars, and, when they find them, lay eggs either on or inside the worm. The wasp larvae hatch and eat their way to adulthood inside the caterpillar. They may or may not kill it, but they consume enough of its tissue so the caterpillar cannot pupate and become an adult. I once found a tomato hornworm with little silk barrels on its back. You guessed it: wasp pupae. "Thanks for lunch!" If you saw any of them, the three Alien movies stole this theme.

There are no visual cues here. The wasps sniff out their prey. Could chemical mimicry be going on? Could this pressure drive a caterpillar to smell vaguely floral or even have multiple, confusing odors?   I don't know, but I do know that some plants that are damaged by feeding caterpillars release a chemical that attracts wasps!

What will they "think" of next?