The term inchworm refers to the larval stage of moths belonging to the Geometridae family. Inchworms are not worms, so to speak. They are caterpillars, and there are approximately 1,200 known species living in North America. They are considered pests in agricultural areas as well as backyard gardens due to their destructive eating habits.

Geometridae on plant in the wild
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Inchworm Habitat

Inchworms do not get their name from their size. Most inchworm species are only about 1 cm in length. Instead, they are so-called due to the way they move. Inchworms have three pairs of legs in the front and two in the back, which create their characteristic "inching" movement as they move forward.

Common Natural Habitats

Inchworms generally live in areas with dense tree populations. Depending on the species, inchworms will enjoy spending time in apple or other fruit groves, or oak or elm forests. However, any deciduous trees are fair game to these caterpillars. Vegetable gardens, especially where celery, cabbage or radishes are being grown, are also on the menu. Both commercial farmers and home gardeners alike battle inchworms due to the broad inchworm diet.

Other common natural habitats for inchworms include linden trees, sweetgum, conifer trees, broccoli, kale, parsley, peas, potatoes, cauliflower, brussels sprouts, lettuce, beans, tomatoes and other garden crops.

Inchworm Distribution and Range

Inchworms can be found throughout North America and Europe. They travel from place to place through a method known as ballooning. This technique involves the formation of a single strand of silk that the worm produces as a way to escape predation. When an inchworm is threatened, it produces a tiny, single strand of silk, which it attaches to a leaf or branch. It drops down off the tree to escape a predator. In certain circumstances, the wind catches the strand of silk and blows the worm to another location.

Methods for Controlling the Inchworm Life Cycle

Because many inchworms have developed a tolerance to pesticides and are prolific breeders, they live in every agricultural area, though they are particularly prevalent in areas that grow fruit such as Florida and California.

Inchworms cause thousands of dollars in devastating damage to fruit crops every year. They chew the leaves and make it impossible for the plants to gain nutrients from the sun through photosynthesis. They also weaken the plants' overall health, resulting in smaller and weaker plants. If the plants do bear fruit, the inchworms eat those as well. Even minor cosmetic damage to a fruit can deal a devastating blow to a farmer's bottom line.

Instead of conventional pesticides, biological measures such as introducing predatory wasps and infectious fungi have been implemented in many cases to keep them in check. Other products to try include neem oil and diatomaceous earth. Picking them off plants by hand may be practical in very small home gardens, but it must be done on a daily basis in order to be effective. Green inchworms can also be difficult to see given their color against the plant leaves, not to mention their small size.

Active Seasons for Inchworm Populations

Inchworms of various species can be found active in either spring or fall. The entire inchworm life cycle, from egg to mature moth, is spent on the trunks of trees or on vegetable plants. Adult females lack the ability to fly and will remain on the same tree in which they pupate. The males do have the ability to fly and will move from tree to tree or plant to plant in search of females.

Inchworms spend around two to four weeks in the destructive larval stage before they transform into the adult moths. But because they reproduce so rapidly, there are always plenty of inchworms to fight in the garden.