They move along in a very distinctive style and they can destroy trees – those cute little inchworms! They have voracious appetites, like any insect in the caterpillar stage, and inchworms have a particular fondness for a wide range of trees. Inchworms feed on the leaves until only the bare skeleton of dry veining is left. In time, the entire tree is decimated, unsightly, and damaged in extreme cases.

Inchworms go by many names, including cankerworms, spanworms, and measuring worms. They are sometimes mistakenly identified as loopers, which is incorrect as these fall into the Noctuidae group. Their familiar crawling style – the middle arches as the rear end catches up – is attributed to their lack of legs in the midsection. Inchworms can be any one of a number of species that are members of the Geometridae moth family.

Common species include fall and spring cankerworms and the winter, or gypsy, moth. Caterpillars can emerge at varying times of year after pupating underground. The adult females are beetle-like and wingless and must crawl up tree trunks. Eager males hover in a cloud for breeding. The eggs are laid among the leaves and the trouble begins.

Any deciduous tree is susceptible to inchworm damage. The list includes:
-apple
-ash
-basswood
-blueberry
-crabapple
-hickory
-maple
-oak.

Inchworms are partial to fruiting species across North America and in Europe may also attack evergreens such as spruce. The caterpillars crawl into the budding portions and begin chewing. Once the leaves open, signs of holes and a lacework pattern appears. When inchworms are alarmed, they develop a single strand of silk and drop from the leaf. The string hardens and they can climb upward and continue their meal until the leaves are stripped. Inchworms sometimes infest vegetation beneath the tree, however. If caught in the wind, the caterpillars can travel in a process called “ballooning.”

Several treatment methods are available, including a decision to do nothing if the inchworm sightings are minimal. Parasitic wasps and flies are one preventative that is also safe for the environment. Chemical insecticides such as Malathion and Sevin can be effective in the caterpillar stage. Read labels carefully and follow directions.

Danger from inchworm feeding is not always severe and does not occur every year. Mature, healthy trees that receive less than 25% damage, even two years or seasons in a row, should recover with little effort. On the other hand, one or two severe defoliations may kill part or all of the branching systems, leaving the tree stressed. Watering can help in recovery from inchworm attacks.

Originally posted 2007-05-28 08:37:15.