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.
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.