Any caterpillar that creates silken-looking webs are all commonly referred to as ‘The Bagworm’. There are three distinctly different area Bagworms in Northern Illinois: the true Bagworm, the Eastern Tent Caterpillar, and the Fall Webworm.

BAGWORM

The Bagworm (shown here) first arrived North of Highway I-80 in 2006. It is undoubtedly the most damaging of these three insects. The Bagworm attacks a wide variety of trees and shrubs; most notably Colorado Blue and Green Spruce, Locust, Maple and Arborvite. We have also found them on other trees and plants too numerous to mention. Each of the cone shaped pods contain one egg-laying female which will produce 500 to 1,000 offspring the following year. Calculate that year after year, and you can see why this insect spreads so rapidly.

Pods up to 2” long are made of interwoven bits of foliage from the host plant, tied together with a silk threading. In spring and early summer the female Bagworm drags the bag around its host plant to feed. In late August, it attaches the bag to a twig. Male Bagworms, now in their moth stage, gravitate to the bags to mate. The female inside lays her eggs and dies off. The following spring, the 500 to 1,000 newly hatched caterpillars crawl out and immediately begin feeding, starting the process all over again. Infestations of these insects, left untreated, will kill their host plant in fairly short order. On deciduous plants they leave a highly weakened and unsightly plant in their wake.

Hand-picking the individual pods off of low-growing plants will control ‘some’ of the problem. We say ‘some’ because many will be missed. Tree spraying, systemic trunk injection or soil drenching of approved insecticides at the proper time works much more thoroughly.

These are the caterpillars most of us are familiar with. They create large, silken nests either in the crotches of limbs or on the ends of branches. Nests that can be safely reached on the ends of branches can be cut off and burned, or sealed in a plastic bag and disposed. The bags should be cut off just prior to dark, as most of the caterpillars will be back inside the nest for the night.

Nests in the crotches will require pressurized spraying applications, as cutting is not an option.

Untreated, these insects can completely devour an entire tree or very large sections of it. As with all insect and fungus situations, proper timing and product selection are of the utmost importance.