It’s hard to hate the caterpillar. Maybe because there’s something Alice In Wonderland about it or because it’s such an odd word. Maybe because it is often hairy and not slimy like slugs or creepy like earwigs or because of its alien-like (or are aliens like caterpillars?) life-cycle; they go from the egg to larva (the caterpillar) to pupa (chrysalis) to the butterfly (which delights us all) and carry on like that ad infinitum. David Attenborough told us in July that butterflies were having their worst year since the 70s ( http://www.guardian.co.uk/environment/2012/jul/12/david-attenborough-butterfly-count ), though apparently not these cabbage butterflies (see the happy collection of their caterpillars below).
Caterpillars can do a lot of damage to leafy plants and organically-inclined gardeners have a constant battle with wanting to save our precious brassicas (kill the caterpillar!) and wanting to save the planet (don’t kill the caterpillar!). The one in the picture above (soon to be/previously a cabbage butterfly) has decided, with its friends or relatives, to vary its diet and feast on nasturtiums. Caterpillars can get through a lot of leaves, and that inhibits the plants’ ability to photosynthesise. It also means there is less leaf for you to eat.
I’m willing to sacrifice the nasturtiums (they are strangling my herbs anyway) and even the kale (who needs kale in summer?) but not my red cabbage. So what do I do? What I should have done, the organic gardener’s first resort, is to check the leaves more often so that I could spot and squish the eggs. I could also have killed the caterpillars at this stage and then composted them. I was too squeamish for that. The last resort would be to spray with a microbial pesticide which contains living micro organisms (such as bacillus thuringiensis Bt) which will kill the caterpillar through its gut. It is safe for other insects, so less damaging environmentally than usual pesticides. But I’m not going to do that. My airy fairy idea is that this caterpillar population explosion will provide delicious and nutritious food for birds and beetles and that a balance between the caterpillar’s role as pest and and as food will come.