27 September 2006

Eastern tiger swallowtail

eastern swallow  tail caterpillar

This is the 4th instar of the eastern tiger swallowtail (Papilio glaucus). I photographed it one recent evening in the woods after a late afternoon rain. It was climbing up the wet trunk of a young beech (I turned the picture sideways for your viewing pleasure).

According to Wagner (Caterpillars of Eastern North America, Princeton Field Guides, 2005), the graded lightening of the sides of this caterpillar's body from the top to the bottom is an example of countershading. This makes the parts that would receive less light appear about as light as the top receiving more light, thus rendering the caterpillar more uniform in color and, consequently, more difficult to be detected by visual predators, such as birds.

And, of course, this is what the adults look like.

eastern swallow  tail

3 comments:

clare said...

The grading of the colour is very interesting - but is there also an explanation for the yellow and grey spot on the side (is it meant to look like and eye, for instance - though this would not make much sense, really, would it?)

AYDIN ÖRSTAN said...

I don't know the function of that spot.

clare said...

Looking at the butterfly it seems a little like a hint at what is to come - a repeating motif along the edge of each wing.