Inchworms often are recognizable by their signature movement as they crawl along a tree branch, but these worms -- which are actually caterpillars -- are more than just fun to watch in the summer. They're the larval stage of moths of the Geometridae family. They spend their caterpillar stage eating and growing so they can pupate and metamorphose into moths.
The easiest way to identify inchworms is by their movement. Inchworms, also called cankerworms, bend their smooth bodies upward in the middle, bringing their hind prolegs up to meet their front true legs -- the legs that will remain in adult moth form -- then pushing their front legs forward to extend their bodies again. It looks almost as if the worms are measuring the tree branch as they walk.
Measuring Inchworm Size
Although they aren't measuring their living spaces, you can almost measure yours using the caterpillars. Most inchworms grow to be about an inch long, so their name is pretty accurate. They start out tiny -- barely bigger than the eggs they hatched from. They spend about three months growing to their final length before they're mature enough to pupate.
Inchworms appear in a variety of colors, including green and brown. Several shades of green exist, and the brown ranges from a reddish tone to nearly black. Many of the brown inchworms sport light stripes that run lengthwise down their sides. These caterpillars produce white silk, which they use to start hanging down from branches as they mature. When it's time to pupate, they let themselves down from the tree branches until they touch the ground, where they burrow down a few inches and spin silk cocoons around themselves.
Seeing the Damage
Even if you don't see the caterpillars right away, you might notice the damage to your trees. They inhabit a number of trees including maple, oak, hickory, apple and elm. They start by leaving tiny holes in the leaves, giving them almost a lace look. Inchworms eat voraciously, but their small size keeps them from doing serious damage to the trees. Some years support more inchworms than others, but they rarely do permanent damage to the trees.
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