On Monday, I asked for a couple of reasons why this Io caterpillar is unusual, but I think I believe I was way too vague.

The answer I was looking for was: It will become a beautiful Io moth. Female and male Io moths are picture below.

Even so, Janet T. came through with quite an answer:

"Perhaps you were referring to the caterpillars' habit of traveling en mass with their siblings which all hatched out of the same egg mass. Or perhaps the fact that they start out their larval stage reddish brown, but after a few molts they are that beautiful bright green. Interesting facts, but perhaps there is something else about these caterpillars I may have missed?"

Sorry about that!  (Great answer, Janet!)

Wikimedia Photograph taken by Patrick Coin