A question from a reader:
If I want large white butterfly caterpillars in my garden AND I want my kale, is that like trying to have my cake and eat it? I suppose they don’t eat anything else, do they? I have sent you a photograph.
I am afraid that kale is the thing that large white caterpillars (pieris brassicae) like best of all. They do eat other things but not with quite so much relish: nasturtiums and the wild mustards are your best bet. Hedge mustard, field mustard (known around here as charlock) and garlic mustard are fairly easy to find. Whether it’s going to be fairly easy, or even possible, to translocate large white caterpillars to them is another question entirely.
 Hedge mustard (Sisymbrium officinale);  charlock or field mustard (Sinapis arvensis);  garlic mustard (Alliaria petiolata)
The female large white lays her eggs in small clutches so the newly hatched caterpillars will be in an easy-to-find group; you could try picking their whole leaf and moving them to a suitable bed of garlic mustard in a nearby hedge or somewhere in the park. It might work. Next year, try growing a row of diversionary nasturtiums in your cabbage patch or plant a few sacrificial extra cauliflower plants just for the large white caterpillars. Kale is delicious but butterflies are extraordinarily beautiful insects.
 Large white eggs and newly hatched caterpillars on brassica;  Late instar caterpillars on nasturtiums