Evergreen Bagworm

Thyridopteryx ephemeraeformis — the evergreen bagworm — is one of the most extraordinary case-bearing caterpillars in North America and one of about 1,300 species in family Psychidae (the bagworm moths — characterized by the diagnostic case-bearing larvae). The species is widespread across the eastern and central US from southern New England south through the eastern US to northern Florida and west to Texas. The species' biology is unlike most Lepidoptera. LARVAE construct distinctive 'BAGS' or 'CASES' of silk and host plant material that they DRAG WITH THEM throughout the larval period: each larva spins a tubular silk bag (typical mature bag size 3-5 cm long) and DECORATES the bag with small cuttings of EVERGREEN NEEDLES OR LEAVES from the host plant (the bag becomes camouflaged against the host plant background through the attached plant material). The larva remains inside the bag throughout development, extending only the head and front legs out of the front of the bag to feed on host plant tissue and to walk by dragging the bag along. The bag is enlarged as the larva grows — the larva continually adds silk and plant cuttings to the bag throughout the larval period. The bag-bearing larvae are major economic PESTS of evergreen ornamental plants — heavy infestations cover Eastern red cedar (Juniperus virginiana), arborvitae (Thuja), juniper, and other evergreens with hundreds-to-thousands of dangling bag cases that defoliate the host plants and disfigure ornamental landscape plantings. The species is the focus of major NA ornamental nursery and landscape pest management programs. The species' MOST EXTRAORDINARY biology comes in the ADULT STAGE. Adult ovigerous FEMALES NEVER LEAVE THE BAG — at maturity, the female pupates inside the bag, and emerges from the pupa inside the bag as a WINGLESS, LEGLESS, EYELESS, almost grub-like adult that remains permanently inside the bag for her entire reproductive life. The female has lost essentially all adult Lepidoptera features (wings, legs, eyes, mouthparts, antennae) — she is reduced to a soft sac-like body that produces eggs and pheromones. Adult MALES are completely different — winged, legged, eyed, with the typical adult moth body plan; males emerge from their bags and FLY in search of pheromone-emitting females in their bags, mate with the female THROUGH THE BAG OPENING (males extend the abdomen into the bag for copulation), then die within hours. The female-never-leaves-bag biology is one of the most-cited examples of EXTREME SEXUAL DIMORPHISM in modern Lepidoptera. Females lay 500-1000 eggs INSIDE THE BAG, where the eggs overwinter and hatch the following spring as tiny first-instar 'crawlers' that emerge from the bag, disperse on silk threads (BALLOONING, similar to spider dispersal), and locate new host plants where they begin constructing their own bags. The species is harmless to humans but is a major economic pest of NA ornamental landscaping.