Some garden worms hide well in plain sight

August 12, 2018

Your tomato plants were doing just fine. Then one day you notice that a couple of big tomato branches are missing almost all their leaves. What happened?

Look closely at those branches. You’ll probably find a huge camouflaged worm that has a horn-like tail.

It’s a tomato hornworm or the closely related tobacco hornworm. Each can grow up to 4 inches long and destroy a lot of foliage. For a creature so big, I find it amazing that it can hide so well in plain sight.

In a home garden, the amount of damage to tomato plants and related crops like peppers and potatoes seldom demands control of the worms. By the time you notice a hornworm, it is probably about finished eating anyway and will soon drop to the ground, dig down a few inches, and pupate. If you let it complete its life cycle, there’s a reward: from the pupa will emerge a large sphinx or hawk moth. Active in the twilight, the moths resemble hummingbirds and are fun to watch as they dart from flower to flower feeding on nectar.

If you want to get rid of any hornworms that are devouring the foliage of your tomato plants or maybe taking an occasional bite out of the fruits, these worms are easy to handpick into a bucket of soapy water: they’re big, slow moving, and seldom present in large numbers. Just take a good look at the hornworms before you destroy them: If you see a cluster of white projections on the back of a worm, leave that worm alone. The projections are the larvae of small wasps which are already parasitizing that hornworm. They will not only kill it but will also be able to complete their life cycle and multiply, helping to control future populations of hornworms in your garden.

The same tiny parasitic wasps that help control hornworms are also enemies of the annoying tomato fruitworm. That’s the worm sometimes found inside a ripe tomato, along with some poop and decay. Needless to say, the damaged fruit isn’t edible. This worm isn’t too picky about what it eats. If it’s dining on corn, it’s called the corn earworm. And if it’s damaging cotton, it’s called the cotton bollworm. Smaller than the hornworm, the tomato fruitworm is 2 inches long or less.

To attract the tiny wasps that parasitize both kinds of worms, I plant some of the wasps’ favorite flowers right with the vegetables. Cosmos, marigolds, and sweet alyssum are a few flowering annuals that are easy to grow from seed and look pretty, while also ensuring that the wasps have plenty of nectar nearby.

The population of parasitic wasps increases even more when gardeners refrain from using pesticides whenever possible and, as a last resort, use only the least toxic products.

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