I found a link that explained that since the oak leaves have so few nutrients the caterpillars digestive tract utilizes the available nutrients ....blah, blah, blah...I got bored and stopped reading. There is some reason for the poop - oops, the frass - to be shaped that way and it has to do with the caterpillars getting their vitamins and minerals.
Either that or caterpillars have a well-developed sense of humor; are up in the oak branches laughing at the humans below who are looking confused.
