Click on all the photos to enlarge.This Eastern Tiger Swallowtail caterpillar (Papilio glaucus) showed up on my garage door last evening. Normally when I see them they are very green but this little critter had already turned brown to blend in with the surrounding door. According to David Wagner in Caterpillars of Eastern North America, this is called countershading, “a strategy among caterpillars that helps them avoid detection by birds and other visual predators.” He goes on to say, “Countershading is achieved with graded lightening of the sides of the body: those portions of the body receiving the least amount of light, and that would normally appear darkened, end up resembling the dorsum (bottom).” You can certainly see that at work here. In fact the modeled color on the back and sides looks almost like the side of the garage door. When they are real young (early instar) they look like bird droppings. Just before pupating and making a chrysalis they turn this brown color.
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