While many varieties of inchworm go by the name “caterpillar,” the term “inchworm” applies to a larvae of the moth family Geometridae, which, according to Ask the Exterminator, contains up to 35,000 species. The Columbia Encyclopedia describes inchworms, also known as cankerworms, as black, brown or green creatures, so named because of their size, that often display lumps or uneven projections as a twig-like camouflage. This harmless-looking insect does considerable damage to trees and vegetables.
Inchworms have fewer legs than most varieties of caterpillar, claiming the normal three pairs at the front end but as few as two pairs of appendages known as prolegs toward the rear. As a result, they have a distinctive way of propelling themselves forward. According to the Columbia Encyclopedia, an inchworm will grip the surface with its forelegs and push its rear portion forward, causing the middle part of its body to elevate, then push its front portion forward while using the prolegs to grip the surface.
Ask the Exterminator states that the inchworm begins its life by hatching from an egg attached to the underside of a leaf. According to the Texas A&M Agricultural Extension Service, inchworms feed continuously for up to one month before making their way to the ground, where they spend a season pupating or transforming into moths. This process may occur from fall to early spring or from spring to late fall.
Inchworms have voracious appetites as they take in the energy required for them to reach the pupal stage and mature into moths, according to Ask the Exterminator. The larvae begin eating the nearest leaf from the instant they hatch. Inchworms display a preference for the leaves of apple, crabapple, mulberry, maple and other fruit trees. They also eat leaves from garden vegetables, making them a pest to farmers and gardeners alike.
Some species of inchworm gather together in trees and spin a large protective cocoon over the entire group, giving the assembled inchworms free reign to feed on the tree’s leaves without intervention from predators. These inchworms can also spin a kind or rudimentary web to escape from threats, dismounting from a leaf and hanging from a silken thread until danger passes and then climbing back up to continue their meal.
While the inchworm may present a harmless enough appearance, it can wreak havoc on vegetation in farms or gardens, according to Ask the Exterminator. The “group-cocoon” varieties such as the eastern tent caterpillar can destroy a tree within a single growing season. Inchworms can also devastate crops of beans, Brussels sprouts and peas unless growers introduce some measure of population control. Allowing more wasps into these areas adds a natural inchworm predator to the environment, while non-poisonous pesticides can also reduce the infestation.