Bagworm

Host Plants

The bagworm feeds on a wide variety of trees and shrubs, but is primarily a pest on coniferous and broadleaf hosts, including arborvitae, juniper, pine, spruce, apple, basswood, boxelder, elms, black locust, maple, sycamore, oaks, persimmon, poplars, and willows.

Regions impacted

North, South, and Central America.

Description

• The bagworm can be recognized by the bag the caterpillar or larvae forms and suspends from the plants on which it feeds. The bag is made of silk, twigs, and leaves, interwoven to disguise and strengthen the bag.
• The appearance of the bag can vary based on the materials used for construction; when fully complete, it may be 1-2 in. long (30 to 50 mm).
• Male bagworm moths are hairy and charcoal black, with translucent wings and a wingspread of about 1 inch (25 mm).
• Female adults are soft-bodied and grub-like, yellowish-white in color, with no functional legs, eyes, or antennae. Females are proverbial stay-at-home moms as they remain inside their bags throughout their lives.
• The female retains and mates in its caterpillar-like state within its bag. Neither the male nor the female adult feeds. The female lives a couple of weeks, while the male lives only one to two days.
• The eggs are smooth and cylindrical in shape and are laid in volume (500 – 1,000 eggs) inside the bag.
• Young larvae hatching from the eggs are small (approximately 2 mm long) with glossy black backs and a dull brown undersurface to their bodies. The fully grown larva is approximately 1 inch (25 mm) long and takes up to four months to develop, depending on temperature.

Life Cycle

• Bagworms have one generation per year and overwinter as eggs inside the bag the female constructed the prior fall.
• Eggs hatch in May or June as young larvae crawl out the bottom of their bag. They almost immediately begin to construct their own bag; some will spin long strands of silk to help them transport via wind to more preferred hosts.
• As the larvae grow over the eight to ten-week feeding period, they continue to enlarge their bags, eventually becoming large enough to enclose the entire insect.
• Larvae move around carrying their bag with them. The bag has an opening at the top, through which the head and several segments protrude when the larva is feeding, moving, or working on the bag.
• Larvae mature from August through September, anchoring their bag to a twig or branch with strands of silk. After securing and then closing the top of the bag, the larvae reverse position in the bag so that their heads face downward.
• They then pupate and remain in this life stage for about 4 weeks. During September and early October, the males leave their bags and fly to bags containing females, where mating occurs.
• Females remain within their bag, so mating occurs through the bag opening. Each mated female deposits a mass of eggs (500-1000 )in the empty pupal case within each bag. Adults die, and eggs overwinter within their mother’s bag.

Damage and Detection

• Bagworm larvae injure plants as they feed on needles and leaves. Initial damage on trees by young larvae have a modest impact; branch tips may appear brown and a bit sparse.
• As the larvae mature, their feeding damage becomes more apparent and serious, causing defoliation of varying degrees and even death. Evergreen species are particularly vulnerable because their leaves are not replenished as readily as those of deciduous trees.
• Bagworms can develop into localized infestations as larvae may move only a few yards or meters from their mother’s host plant resulting in high populations on some plants, including recurring infestation on the original host. Bagworm infestations generally go undetected until damage is complete, and the large bags become conspicuous.
• Early detection of an infestation requires careful examination of host plants for the presence of small bagworms attached to the leaves or needles.

Prevention and Control

Cultural control

• Handpicking bagworms and placing them in a bucket of soapy water or a sealed bag is an effective method when populations are manageable and, importantly, reachable.
• Handpicking is most effective from late fall to early spring before adults reproduce and new bagworm larvae disperse.
• Because they are so conspicuous, overwintering bags and the eggs they contain can be picked from small trees and shrubs and then destroyed.

Insecticides

• When bagworms are too numerous or otherwise hard to handpick, chemical insecticide control may be required.
• There are certain biological insecticides available as well. Penetration with insecticides, however, can be challenging due to the protective bag.
• These products should be applied from early to mid-June while the larvae are small.
• Be sure to follow all insecticide label directions.

Natural controls

• Predators of bagworms include mice and sparrows.
• To attract sparrows to your garden, plant blackberries and wild grasses. You may also attract them with sunflower seeds, cracked corn, oats, and buckwheat.