Luna Moth Caterpillars (Actias luna) are such a bright lime-green they almost appear translucent. We found about a dozen caterpillars on a couple of sweet gum saplings growing along side the road just up from the house.
From a distance, the Luna Moth caterpillar does an excellent job of looking like a leaf. The weak subspiracular stripe on abdomen and yellow lines that cross the larva's back near the back end of each segment look like leaf veins. We'd probably walked passed these caterpillars many times before noticing them. I actually found the caterpillars by first noticing the eaten leaves on the sapling. I then started looking for the caterpillar that had done the damage.
The larger caterpillar is in its fifth and final instar. I'm not sure about the smaller. Even if the eggs are laid at the same time and they hatch at about the same time, caterpillars often pass through their instars at different rates. (Note: The anal proleg edged in yellow is one of the identifying characteristics of a Luna Moth caterpillar.)
Luna Moth caterpillar demonstrating the coordination between its six true legs and mouth. It's dining on sweet gum in this case. Hickory, walnut, persimmon, and birch are also common host trees. The caterpillar must eat enough now to sustain it through the adult stage of its life cycle because adult Luna Moths are incapable of eating.
For more information on Luna Moths, please see:
BugGuide Species Page.
BugGuide photos of all five caterpillar instars.
Butterflies and Moths of North America.
Animal Diversity Web.
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