Bagworms of Missouri

  • Published: Friday, June 11, 2021

Bagworms of Missouri
By Andy Luke, Field Specialist in Agronomy

Calls have been coming in to the Extension office recently about bagworms. The bagworm is an interesting pest that feeds predominantly on evergreen species such as junipers, cedars, pine and arborvitae, but will also feed on nearly any shade tree or shrub species. Host plants are usually partially defoliated, weakened and unsightly, with complete defoliation occasionally occurring.

It is easy to spot a bagworm infestation because of the noticeable silken bags often seen hanging from branches. The bags are carrot-shaped and resemble a Christmas tree ornament hanging from a limb.

From late May through mid-June, bagworm larvae will hatch and begin emerging from the bags. Each larva will begin producing its own protective bag almost immediately. The bags are created from the foliage that it feeds on, and as the larvae grow, their bag is enlarged. Bits of twigs and leaves are incorporated into the bag for strength and camouflage.

Once a host plant is defoliated, the larvae will crawl off with their bags attached and search for a new host. The migration occurs by walking, so the spread of bagworms is relatively slow. At any sign of danger, the bagworm can retreat into its bag for protection. By mid-August, the larvae are mature and will firmly attach their bag to a twig, close the open end and pupate within. During September, the adult males emerge and search for females, mating with them before dying. The females never leave their bags, but will lay between 500 and 1,000 eggs within their bag before dying. The eggs remain in the bag before emerging the following spring.

The easiest way to control bagworms is to hand pick them off and destroy them. Where hand-picking is not practical, several insecticides are effective if applied at the right growth stage. Right now, directly after the eggs are hatching, is the most effective time for insecticide applications. As the size of the larva and bag increases throughout the season, bagworm control becomes much more difficult. For a list of effective active ingredients, search for The Bagworm in Missouri guide sheet, or contact your local Extension office.

Writer: Andy Luke

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