If you can see the green caterpillar then most likely it's the cabbage looper. Sometimes called an inchworm. I just flick them off into a coffee can with some detergent and water. You can use BT which kills them by being systemic. That means it is actually inside the plant and the plant is now deadly to the worm. I've never used it since it MUST have some effect on the rest of the world. I'm probably being a bit paranoid there. Try the detergent first. The damage to your plant, going by the picture, isn't severe as yet. By the way, those cute little white butterflies we see all summer are the culprit. Some people spray a little cheap vanilla extract on the plants and it seems to confuse the butterfly (moth). They go everywhere and apparently recognize your brassicas by aroma. Makes sense. Then they lay their eggs and along comes the hungry caterpillar. Hope all this helps somewhat. Best wishes with your plants.

Likely caterpillars of one kind or another. Don't know which specific ones are busy at your place, but the key is to look closely at top & underside of leaves. At my place, the current bad guys on the cabbage family crops are these: 1. imported white butterfly (cats are up to 1 inch long, velvety green color helps them bled into the leaf. 2. diamondback moth -- very small cats, about 1/4 inch, also small pupal cases webbed to the leaf. These cats make "windows" (eat cells on surface, only) also holes.

I was going to ask if you had deer in the area but you already mentioned it a couple of entries ago. When I looked at how neatly all of the leaves of your broccoli were nipped off the first thing I thought of was deer. We live way out in the sticks, so to speak, and have a lot of deer. This evening I saw 6 does out nipping off the tops of my wildflowers. This spring a doe and her yearling fawn managed to break through a weak spot in the 8' fence we have a around the garden. All of my broccoli and brussels sprouts were nipped off as cleanly as yours appear to have been. I'm betting your local deer are the culprits. The cages you built should take care of the problem nicely. Good luck with your next crop of broccoli. Actually, if you haven't pulled the damaged plants yet they may recover. Mine did and I'm harvesting wonderful plate sized heads of broccoli now. Gail

You have to be able to identify the culprit in order to treat or prevent. If you can post clear, detailed photos of the damaged plants, we might be able to narrow it down for you.