Attack of the Tomato Killers

Beth discovered something lovely living on our single tomato plant on our patio yesterday. While checking out the 11 golf ball-sized tomatoes that we have growing, a little half-inch green caterpillar was poking it's head out of one of them. She got rid of that tomato immediately. Then, today she found another one. The little green caterpillars were young hornworms - either Tobacco Hornworm or Tomato Hornworm (it was hard to tell since they were so small). From a gardener's perspective, this is not a good sign since these things can get up to 4 inches long and do some serious damage to a tomato plant. From a naturalist's perspective, this is a pretty cool caterpillar.

A Hornworm is the larval stage of a sphinx moth (family Sphingidae) - Five-spotted Hawkmoth in the case of the Tomato Hornworm and the Carolina Sphinx Moth in the case of the Tobacco Hornworm. Sphinx moths are really cool since they fly like hummingbirds while feeding on nectar from flowers. The familiar Hummingbird Clearwing is also a member of the sphinx moth family.

Hornworms start out as eggs laid on the underside of the leaves of their host plants (tomatoes and tobaccos). They hatch and grow while eating the leaves, stems, and fruits of the plants. If the hornworm survives to be fully grown, it will burrow into the soil to pupate. The pupa (cocoon) might remain in the soil all winter to emerge as a moth the following spring, but if the weather conditions are right, the moth may emerge in as little as two weeks.

For a gardener, the best way to rid yourself of hornworms is to hand pick them from the plants, although they can camouflage extremely well. Fortunately, there is a natural parasite that helps control populations - the braconid wasp. These wasps lay their eggs on the hornworm and the larva feed on their insides. The larva eventually pupate and appear on the backs of the hornworms. You can see what a parasitized hornworm looks like here - yuck!

Here is a picture of our little hornworm buddy. Unfortunately, he will not survive to be a moth...