The bagworms belong to the superfamily Tineoidea, which is a basal lineage of the Ditrysia (as is Gelechioidea, which includes case-bearers). The family is relatively small, with about 1,350 species, who are found almost everywhere.
Despite their name, which comes from the worm-like form of the larvae, these insects aren’t worms but moths.
The bagworms live their entire life cycle inside the safety of their bag, which they construct using silk and interwoven bits of foliage. These bags are created when the larvae attache bits of plant debris, such as leaves, twigs, and bark, to their bodies using a silk-like thread they produce. As they grow bigger, the bag gets bigger too.
The eggs of a female moth hatch in late spring or early summer.
Only the adult male moth leaves the protection of its bag when ready to mate while female moth doesn’t leave her bag.
Bagworms usually infest evergreen and deciduous trees and the bags they construct sometimes resemble a cone so people may overlook them at first glance.
Their favorite host plants are cedar, arborvitae, juniper, and false cypress, but in the absence of these preferred hosts, bagworm will eat the foliage of just about any tree: fir, spruce, pine, hemlock, sweetgum, sycamore, honey locust, and black locust.
Although they seem harmless, bagworms actually cause significant damage to the trees. The issue is that they hide until the infestation is severe.
As they feed on the leaves of the tree, it makes it more difficult for the tree to photosynthesize and produce the nutrients needed for growth and survival.
At the same time, they make the tree weaker, and with that, more prone to diseases, attacks from other pests, and environmental stressors. If not treated for bagworms, the tree can eventually die.