Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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Do Caterpillars Know Where They Are ?

I found a patch of bur marigolds (named for their tick-like seeds that stick to pants, and are not actually true marigolds but in the composite or aster family in the genus Bidens ) in our marsh and was enjoying the beautiful yellow flowers when I noticed a dark caterpillar on one of the flowers (see photo).

Now this pug caterpillar, which is the larvae of a geometrid moth in the genus Eupithecia, feeds on many different plants and often the flowers of composites such as the bur marigold. The surprising thing about this is that the caterpillar is clearly designed to be cryptic and camouflaged in brownish vegetation, but is extremely obvious and likely subject to predation by birds with this yellow flower as a background. Indeed I noticed it because it contrasted with the background. So what is this caterpillar doing- does it have a death wish?

This raises the question whether caterpillars have any idea of what color they are and what type of background will protect them from predation. Or do they just mindlessly seek out their characteristic food plant for which they are best suited. However this pug caterpillar has a problem since it feeds on a wide variety of leaves and some flowers. The interesting thing is that there is an indication that these caterpillars change color depending on their food, and thus come to resemble their background in time. This would be a very sophisticated response to their wide taste in food, but it does not answer how they manage to survive long enough to adapt their coloration to their chosen background. One way would be to feed at night and hide under the flower during the daytime.

So watch out for caterpillars that do not seem to match their background. I suspect this is a rare occurrence.

Bill Dunson
Galax, VA & Englewood, FL