Cabbage White Caterpillars and Butterflies

2015 December 26

Sandy planted some broccoli in one of our raised beds in the spring of 2015, and by the end of June we started seeing a combination of tiny caterpillars eating tiny holes in the leaves,

bigger, green caterpillars eating big holes in the leaves,

and a selection of chrysalises, some of which were brown,

and some of which were green.

I knew what these were right from the start, of course. They were Cabbage Whites, Pieris rapae, a very common pest of cabbage, broccoli, brussels sprouts, kohlrabi, kale, and collard greens. All of which are technically the same species, so it’s hardly a surprise that the same caterpillar eats them all[1]. Rosie raised some of the caterpillars up to adulthood[2], so here are what the adults look like:

Cabbage Whites are an accidental importation from Europe, with their first appearance in North America being in Quebec around 1860. Since suitable foodplants for them are widespread, they spread rapidly across most of North America, and are now some of the most common butterflies in the country. Anybody who grows cabbage or other brassicas in the garden will see a lot of them.

While they did eat quite a lot of the broccoli leaves, that wasn’t the main problem (the plants grew fine regardless). The bigger issue was that they tended to crawl up into the broccoli heads (along with many, many earwigs). So whenever Sandy harvested the broccoli, she had to shake the heads vigorously to knock out all the caterpillars and earwigs. There were typically five or six caterpillars per head, and maybe 20-30 earwigs most of the time. It was kind of appalling, actually. And has a disturbing implication for the broccoli that you buy in the store: what on earth are they doing to it to get the bugs out? Given what an earwig heaven broccoli heads are, just how noxious are the pesticides that are being used to keep them out in the commercial farms?

[1] It’s actually rather startling what a high proportion of our common vegetables are just various mutants derived from Brassica oleracea, along with its close relatives Brassica rapa (turnips, napa cabbage), Brassica nigra (mustard), and various crosses among the three species (rutabagas, canola, various mustard varieties). When we get the Territorial Seed Co. catalog every year, they list the genus and species name of everything, and about half the catalog is one or another of the Brassicas.

[2] By “raised some to adulthood”, I mean “A whole bunch”. I didn’t actually count all of them, but at one point Rosie had at least twenty caterpillars, most of which matured (although a bunch of them were parasitized by what looked like the same tachinid flies that have been attacking the local giant silk moths). She liked catching the butterflies out of the cage, holding them in her hands for a while, and then taking them outside to let them go.

2 Responses
  1. Katbird permalink
    December 26, 2015

    Earwigs are predators on caterpillars….

  2. Katbird permalink
    December 26, 2015

    Forgot to click on updates.

Comments are closed.