Summary: Inchworms, despite the name, are truthfully not worms at all. They are really caterpillars, which are moth larvae. When trying to identify a specific inchworm you need to consider worldwide the Geometridae moth species that some counts put as high as 35,000. .
The inchworm gets its name primarily because the average species grow to about 1 inch (2.54 cm). Inchworms are not hairy like most caterpillars and they have three pairs of legs at the front of their body and two or three pairs of legs near the back, but nothing in between. They have a very distinctive style of moving that involves standing up on their hind legs and lunging forward, then inching their hind end forward on their back legs.
Inchworms hatch from eggs on the underside of leaves and begin eating immediately. They are generally little more than walking appetites until they pupate and evolve into adult moths of the Geometridae family. One main characteristic of these moths is they hold their wings open and away from their bodies when at rest, whereas other moths fold their wings over their abdomen.
Inchworms are a pest in the garden for a variety of reasons. They prefer several different types of deciduous tree leaves including maple, apple, crabapple, mulberry, and others. Fruit trees are one of their favorite meals causing serious damage to trees when they congregate in a large enough numbers.
In addition to tree leaves, inchworms will eat the leaves of many garden vegetable plants which make them a bigger problem than when they attack tree leaves. It also makes people take an active interest in finding ways to control or eradicate them.
As a defense mechanism to protect itself many inchworms have the ability to spin a web similar to that of a spider. They drop from the leaves where they are eating and swing on a single silk thread until the danger is past. The thread eventually hardens and the inchworm is able to climb back up it to its food supply.
Certain varieties of inchworm like the Eastern Tent Caterpillar, are known to weave cocoons of silk around a collection of the worms to protect themselves from predators while they strip the leaves of a tree completely within the
cocoon. Many people call this a web, but that is not a correct term because the purpose of the structure is purely self preservation rather than any attempt to catch food. These inchworms are the most destructive because they always group together and, if enough are present, they can kill a tree completely in one season.
Characterizations of the inchworm make them likeable by some. In fact, there is a riding toy for children modeled on the shape and movement of the insect that is called Inch Worm. But, this insect pest can be a very serious problem for certain types of trees and shrubs, as well as some leafed crops such as beans, peas, and Brussels sprouts and there is no glamour or likeability factor when they are causing millions of dollars in damages.
So how do you get rid of these things? Well, they do have a few natural predators like birds, paper wasps and yellow jackets. One of the most common methods of limiting the number of inchworms in a given area involves allowing more wasps to survive there. Wasps like to feast on inchworms. Of course, for many people, wasps are not really a good idea for obvious reasons. The inchworm can also be managed using various chemicals or non-toxic “green” products. Try to find their main areas of infestation. If it is in a fruit tree, you may be able to spray the tree and nuke the entire infestation.