Although not necessarily harmful in smaller, controlled numbers, infestations of inchworms can cause severe damage to trees, shrubs, and many varieties of vegetable plants. Methods of removal can include traditional chemical insecticides or more natural types of pest control.
Inchworms go by many different names, including cankerworms, spanworms, loopers, and measuring worms. They generally reach one inch in length and are smooth and hairless. The presence of inch worms can be identified by shaking plants lightly to detect the presence of the worm and larvae, or through careful examination of the branches. Infected plants will have noticeable tiny and irregularly shaped holes between the veins.
Small numbers of inch worms are not destructive to the natural habitat, since many trees and plant life can survive minimal inchworm feeding. When the number of inchworms grows, they can become a destructive pest, often damaging vegetable crops. The inchworm can be particularly destructive once an infestation is present because female moths lay their eggs in both fall and spring cycles.
The type of foliage the inchworm feeds upon will depend on its species. Some prefer trees and shrubs. These inchworms cause damage on apple trees, oaks, and sweet gums. Other species of inchworm prefer vegetable gardens, and will feast upon almost any vegetable you plant, including tomatoes, celery, beans, potatoes, cabbage, and radishes.
The best type of prevention of an inchworm infestation is making sure your lawn or garden is hospital to the inchworm's natural predators. Ground beetles, birds, Trichogramma wasps, yellow jackets, and paper wasps all prey upon the inchworm.
Treatment with chemical insecticides is not recommended and is generally seen as unnecessary. However, if the infestation is large enough to present significant damage, the landowner may opt to use insecticides. The least damaging insecticides include horticultural oils that can be applied to trees, and Bacillus thuringiensis for vegetable gardens. Oils will smother the worms, and Bacillus thuringiensis will cause the body of the worms to rot, while being harmless to humans. These methods may not work once the inchworm is larger than 1/2 inch. In this case, chemical insecticides may be needed to control the infestation.