The Q&A Archives: Little Green Caterpillars: Good Or Bad?

Question: I have a small backyard flower/vegtable garden which I keep pesticide free. In early fall I noticed several green caterpillars with a yellow stripe on the tops of my carrots. I was wondering if these bugs are harmful or helpful. If they are harmful is there anyway to get rid of them naturally?

Answer: There are quite a few green caterpillars. A couple are vegetable pests: cabbageworm or cabbage looper, small (about 1 to 1 1/2 inches long, slim) green caterpillars with white stripes running the length of their back. They make a little "loop" with their bodies as they crawl. Another is tomato hornworm or tobacco hornworm, which is about 2-3 inches long, fat, with white stripes and a "horn" that projects from the rear.

If you catch them early, handpicking them is an easy and effective control. Look under leaves and all around the plant. You can often spot their dark, pellet-shaped droppings which can help you locate them. If they are out of control, you can use Bacillus thurengiensis or Bt. It is a biological control--a bacteria that kills only caterpillars and is safe to other insects, humans and animals. However, it will also kill beneficial caterpillars such as the larvae of butterflies and moths. I'm not sure from your description what you saw. For example, the larvae of a luna moth is also green with slight yellow stripes. Try to capture one of the caterpillars and identify it. The public library should have a variety of references. You can also monitor the damage and see if it is something you can live with. Good luck!

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