Cabbage head troubles

My first attempt at growing cabbage has turned out to be quite a success. The heads are already forming and they look gorgeous.

But when I went to take a peek at them yesterday, my heart almost broke into two. Two heads were infested and nibbled. There were thousands of tiny green eggs inside. I'm not sure what bug they belong to but I doused the heads with plenty of water and then smeared minced garlic all over to prevent future infestation. Not sure if this will work though.