Why Are Insects Deceptive?
In my last post, I talked about mimicry in hickory horned devil caterpillars and I’ve talked about it before. It’s an interesting issue in looking at insect ecology, behavior and evolution. When you start looking for it, you see it everywhere.
Why are luna caterpillars bright green and ribbed? They are mimicking the green, ribbed surface of the leaves they live among, since the leaves are everywhere and don’t attract attention. Birds and other predators don’t eat leaves.
It’s essentially camouflage, and it can be remarkably specific. Remember an earlier discussion I posted in which I talked about how regal moths and their relatives were tropical invaders who breed only in the late summer rainy season? Well, if you think about it, this explains some of the unusual coloration of some of these moths – coloration which, when they come to the light on your front porch, certainly seems to stand out.
Take for example, one of the regal moth’s cousins, the large, bright yellow, imperial moth:
This moth, seen by itself, certainly seems to be showing off rather than hiding… but that’s only because we’re seeing it out of context from the woods in which it lives, during August, the season when it is flying. At that time in the late summer in the south, a number of trees prematurely begin to shed leaves. A common forest tree that does this is the tulip tree. Here is a picture of a tulip tree, taken in the season when these moths are flying:
… and here is a picture of a fallen tulip tree leaf. Notice the resemblance to the color pattern of the imperial moth?
Here are some other members of the subfamily Ceratocampinae, all also late summer flying, all also dead leaf mimics:
Why do they mimic dead leaves instead of the more common green leaves? Remember that dead leaves fall and flit around on the breeze and moths fly. It’s a better match.
Remember my post about the second instar caterpillars (and many others) looking like bird poop? That too is taking advantage of a common piece of the specific environment the caterpillar lives in and using camouflage to blend in with it. Similarly, a lot of caterpillars are also twig mimics:
Why are bugs so deceptive? I’ll talk about this more in a later post, but the short answer is first that, among animals, arthropods are small (their size is limited by the way they absorb oxygen into their bodies) and thus tend to be prey to larger animals (birds, lizards, amphibians, etc.), which means that predator avoidance is a big survival issue. Secondly (and more importantly, really) because they are biologically equipped to take great advantage of the adaptive capabilities of evolution – they produce large numbers of offspring which get heavily “selected” by the struggle for survival – 500 hundred eggs may result in two surviving, breeding adults (if they are lucky); they also breed frequently, producing from one to several generations every year. In short, their genes have a lot of opportunities to try experimental combinations, and, when they hit on some new design that shows some promise, they get to make a lot of drafts to get it right. When you live like this, you can develop some amazing adaptations to fit your environment.
Wagner, David L. 2005. Caterpillars of
Eastern North America. Princeton University Press, Princeton.