Controlling Caterpillars as Garden Insect Pests

Some butterfly and moth caterpillars can be serious garden insect pests. Get tips for controlling these garden bugs.

We usually think of butterflies as creatures of beauty as they flit about our gardens, feeding and pollinating on the flowers. While this is the case most of the time, there are a few species you may not want to see in your backyard. Butterfly caterpillars feed on a wide variety of plants, and most species are not harmful to the vegetation they eat. However, a few are serious pests to plants and trees.

All in all, there aren’t that many “pest” butterflies. Two species that come to mind are the cabbage white and giant swallowtail. The cabbage white (or cabbage butterfly) was introduced into North America from Europe around 1860. Since that time, it has spread over most of the country and has become a serious pest to crops in the cabbage family. In home gardens, these medium-sized white butterflies can ruin a crop of broccoli or cauliflower in a few short weeks. So what can we do to protect our plants?

Pesticides are an option, but if you’re striving to go green and avoid harming many other beneficial species, you might consider some alternatives. In maintaining beautiful yards, we have a tendency to want to spray for pests that occasionally wreak havoc on our plants. However, there are natural chemicals and methods of control that won’t harm the environment. When we use chemicals to control pests, we often kill beneficial insects as well.

Garden InsectsJill Staake
Citrus farmers find the “orange dog” caterpillar to be a pest, but many welcome the Giant Swallowtail butterflies they become.

The other beautiful flying flower that can be a pest to citrus crops is the giant swallowtail, or “orange dog,” as farmers often refer to it. This North American species ranges from southern New England to southern Florida and west to Texas, Mexico and southern California. Orchard growers consider it a pest in many locations because its caterpillars can defoliate young trees, destroying flowers and fruit. This weakens the tree and slows its growth.

First, as with many pest species, picking caterpillars off the plants by hand will help. In the case of the cabbage white, planting thyme, oregano or hyssop near your cabbage-family plants will help repel the butterfly altogether.

Moth caterpillars are probably the bigger problem when it comes to garden insect pests. The spongy moth was introduced into Massachusetts in 1866 from Europe, and it has caused billions of dollars in damage to eastern forests, killing thousands of trees.

The eastern tent caterpillar, native to North America, is a common sight in early spring to people throughout the East. This pesky crawler defoliates cherry, crabapple, apple and other fruit trees from its highly visible web nests. Although most trees recover from this early defoliation, the silk nests are eyesores. Interestingly, birds won’t eat these hairy caterpillars because they can’t digest the sharp-pointed hairs that penetrate their stomach lining. To control outbreaks of eastern tent caterpillars, check your small cherry and other fruit trees in late fall or winter, and remove and destroy any egg masses you find.

Fall webworms are similar to the eastern tent caterpillar. They appear in fall, and the large nests of larvae are located at the ends of branches, usually enclosing leaves. This species is native to North America, and it feeds on more than 85 different species of trees. To control these moths, you should encourage predators and parasites that live in your garden, as they will eat them.

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