Bagworms are insects known for the distinctive, camouflaged bags they construct and carry. These unique shelters, made from silk and bits of plant material, house the creature as it undergoes a transformation through several stages.
The Bagworm Life Cycle
The bagworm life cycle begins with eggs, which overwinter inside the female’s silk bag. In late May to early June, tiny larvae, or caterpillars, hatch. These newly hatched larvae, about 1/25 of an inch long, begin constructing small, conical bags.
As they feed on foliage, the larvae enlarge their bags by weaving in pieces of leaves, twigs, or other debris from their host plant. The bagworm carries this protective case, extending only its head and legs to feed and move. This larval stage, where the insect lives inside its portable bag, is the “bagworm” most commonly observed.
By late summer, the mature larva stops feeding, attaches its bag to a twig or branch, and seals it shut to pupate. This pupal stage is when the insect undergoes metamorphosis into its adult form.
Characteristics of the Adult Bagworm Moth
The transformation inside the pupal case results in adult bagworm moths, which differ significantly between males and females. Adult male bagworms emerge from their bags as winged moths, black and furry with feathery antennae and mostly clear wings. These males are capable of flight, their primary purpose being to locate females for reproduction. They have underdeveloped mouthparts and do not feed, living only for a few days.
In contrast, the adult female bagworm never develops wings and remains inside her bag. She is maggot-like in appearance, soft-bodied, and yellowish-white, lacking functional eyes, legs, or antennae. After mating, the female lays a large clutch of eggs, between 500 and 1,000, inside her bag before she dies. The bag then protects the eggs over winter until the next spring.
Bagworms and Your Landscape
The presence of bagworms in a landscape is noticeable due to their distinctive, spindle-shaped bags hanging from branches. These bags, which can grow up to 2.5 inches long, are often camouflaged with bits of the host plant, sometimes resembling small pinecones.
While adult moths focus on reproduction, the larval stage causes damage to plants. Bagworm larvae feed on the foliage of a wide variety of trees and shrubs, including evergreens like arborvitae, juniper, and spruce, as well as many deciduous trees. Young larvae create small holes, while older larvae can cause significant defoliation. This feeding activity occurs throughout the spring and summer. Heavy infestations can weaken plants and, in the case of evergreens, complete defoliation can lead to the plant’s death because they do not regrow lost foliage.