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....
