Bagworm

The bagworm, most commonly represented in North America by the evergreen bagworm Thyridopteryx ephemeraeformis, is the larval stage of a moth in the family Psychidae. This family is defined by its unusual larvae, which spin protective, camouflaged cases out of silk interwoven with bits of leaves, twigs, or bark from their host plant.

Bagworms are considered a garden and landscape pest because dense infestations can strip needles or leaves from ornamental conifers and shrubs, though the insect itself poses no direct threat and simply feeds as any caterpillar does. Adult male bagworm moths are small, dark, and fly briefly to find females, which remain wingless and grub-like inside their cases for their entire lives.

• Distinctive spindle-shaped case, 38–63 mm long, made of silk woven with small pieces of twigs, needles, or leaf fragments from the host plant.
• The case hangs from twigs and branches, often mistaken for a small pinecone or bit of plant debris.
• The caterpillar itself is dark brown with a mottled pattern, visible only when it extends its head and legs from the case opening to feed or move.
• Cases enlarge as the larva grows, always remaining camouflaged to match the surrounding foliage.
• Lookalike: easily confused with small pinecones, seed pods, or other plant debris due to its effective camouflage.

Found throughout much of North America, especially in the eastern and midwestern United States, on a wide variety of trees and shrubs but with a strong preference for conifers such as juniper, arborvitae, and cedar. Larvae are most active and feeding from late spring through summer, with cases becoming most visible in fall and winter after leaves drop.

The caterpillar feeds on the leaves or needles of its host plant while remaining largely concealed inside its self-made case, extending only its head and front legs to move and eat, dragging the case along. Because a single generation can defoliate sections of ornamental trees or shrubs when populations are high, the species is regarded as a garden and landscape pest. Adult males are small, dark, clear-winged moths that fly to locate females, which remain wingless, legless, and grub-like, never leaving their case even as adults.

Bagworms undergo complete metamorphosis. Eggs overwinter inside the mother's case and hatch in late spring into tiny larvae that immediately begin constructing their own protective case from silk and plant material, enlarging it as they grow through the summer. In late summer, larvae pupate within the case, and males emerge as flying moths to mate with the still-enclosed, wingless females, who then lay eggs inside their own case before dying; most regions see one generation per year.