We don't get very many on our site - don't know why! If we did, I'd grow mine under a fleece or mesh cover.
But when we see the butterflies first flitting around, we know we already have the egg clusters - search around and crush them; ditto for caterpillars.
When the caterpillars are young, a dose of derris dust or liquid will do for them.
I don't know enough about the different caterpillars, but some appear to "feed on the surface", and there's one which burrows deep into the cabbage. Worth getting the little sods early before they're half way through!
All best, Gavin
PS Forgot something - they seem to be particularly partial to certain varieties. I love the taste of Golden Acre cabbage - almost buttery some years. Ah, but so do the butterflies! I quite happily plant an extra 4 or 5 Golden Acre - keeps them happy and diverted, and me happy too!
