@utdavid It could be cabbage loopers or cabbage worms. Someone with a vegetable garden may have an answer tomorrow. You might have to look after dark to see if you can ID the muncher so you can decide what to use to get rid of them. You may only need to pick them off, drop them in a small can, and drown them in some soapy water.
I'd guess these are caterpillars of the Cabbage Butterfly. Did you notice any white butterflies around? I didn't know it, but there are apparently two varieties of white cabbage butterflies -a large one and a smaller one - and the site shows photos of the caterpillars of both as well as of the butterflies. It indicates the smaller one is the more damaging of the two. Link: http://www.downgardenservices....
