2008 February 9

Back in April, while planting some more rhubarb[1], I found this about an inch underground. It had evidently overwintered as a nearly-adult caterpillar


It was still dormant, and wouldn’t unroll for anything. In retrospect, I should have gotten a picture of its back, because it looks like there is a row of black dashes running along the back in this picture, but it is hard to tell for sure with only a side view.

About a month later, while weeding in the same area, I found this one, curled up and hiding in the ground the same way:


This one was not dormant, it was just resting. After a bit it started to uncoil


and crawl off, giving a chance to get some good pictures of its back.


As near as I can find out, these are two different species of cutworm. The green one was tenatively identified by the folks at bug guide as being maybe Noctua pronuba, which has characteristic black dashes along its back. It turns out that this caterpillar changes color as it grows, with the young ones being grass-green, while the ones that are old enough to pupate on their next molt are more brown. As is all too common, this species was accidentally introduced from Europe, and has become very common in North America.

The second one is kind of lacking in diagnostic features, and it’s hard to pin it down any more narrowly than to say it is probably one of the more nondescript types of Owlet Moths, family Noctuidae. It turns out that while some of the moths in this family have very distinctive caterpillars, a lot more just have caterpillars that are these unexceptional greyish-brown eating machines, like this one. Even so, it probably could be identified by someone who was sufficiently expert.

Not that the ID of either of these matters much for practical purposes, given where they were and what they were probably doing. “Cutworms” like these have a habit that is very annoying in gardens: they tend to lurk just under the surface of the soil, and eat off plants at the base. They are murder on seedlings, because they often don’t eat the whole plant, just moving on to cut off another to die, and another, and another . . . In significant numbers they are serious pests in a garden. The species (like these) that overwinter as partially-grown caterpillars are a particular problem, because they come out of hibernation and start chowing down on the seedlings that you just planted in your garden in the spring. And, because they lurk underground, they are shielded from pesticides pretty well, so chemical control is not very useful. Some of the things that can be done are to till the soil either very late in the fall or very early in the spring, which either buries them too deep to emerge, or exposes them to the elements and to birds that like to eat them.

[1] I love rhubarb. Not only is it tasty, but it is one of the few plants that actually grows decently around here – it is originally from the colder parts of Russia, after all, and cold doesn’t really bother it. And I particularly like the fact that it is ready to harvest at a time when there really isn’t anything else available in the garden. And, luckily, it isn’t eaten by cutworms to any great extent.

2 Responses
  1. February 19, 2008

    We protect against cutworms by buying a big package of plastic cups and cutting the bottoms out. Then we plant the tomato plants into these pushed deep in the ground, sticking up about an inch. It isn’t perfect, but it saves about 90% of the plants.

  2. February 20, 2008

    That sounds like a good idea, thanks!

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