Asked October 4, 2013, 3:40 PM EDT

Bagworms have suddenly shown up on trees in yard. What is the best method to halt their invasion onto my trees?

Collin County Texas trees and shrubs insect issues horticulture

1 Response

Bagworm Common Name: Bagworm Scientific Name: Thyridopteryx ephemeraeformis (Haworth) Order: Lepidoptera Description: This insect is usually first detected by observing the bags produced by the larval (caterpillar) stages. Bags vary in size (up to 2 inches long and ½ inch wide) by growth stage (instar) of the larva and between species, and appearance varies with the bits and pieces of host plant leaves, twigs and bark fragments woven in to the silken bag in a shingle-like fashion. Caterpillars of a few other species construct bags or sacks (i.e, case bearing clothes moths, cigar case makers), however, only bagworms incorporate plant debris into the sacs. Life Cycle: Although bagworm species vary slightly in habits and life cycle, on evergreens the bagworm spends winter months in the egg stage within the sealed bag produced by females the previous fall. In the spring (late May, early June), tiny 1/25 inch long caterpillars hatch, lower themselves on silken strands to new foliage and construct a tiny conical bag which they carry upright as they move. As the caterpillar grows through four or more molts (instars), it enlarges its bag. Full grown caterpillars within bags are up to 1 inch long before pupating in August or September. Seven to 10 days later, the pupae of male moths wriggle out of the bottom of the bag before the male emerges, leaving the empty pupal skin behind. Adult males have short ½ inch-long clear wings, hairy black bodies and feathery antennae emerge. They fly and seek out a female to mate. Females do not develop into moths, but remain inside bags and resemble maggots, with no functional eyes, legs, mouthparts or antennae. After mating, females produce a large clutch (500 to 1,000) of eggs inside their bodies and die. Other bagworm species spend winter months as a partially-developed caterpillars that complete feeding and pupate in the spring. Adults emerge in the spring, although some emerge through October. Females produce a clutch of eggs in their bags before dropping to the ground to die. Feeding larvae of all stages occur during the spring and summer. Habitat and Food Source(s): Caterpillars have chewing mouthparts. A wide range of boadleaf and evergreen trees and shrubs serve as hosts for bagworm species, including arborvitae and other ornamental conifers, box elder, cedar, cypress, elm, fruit and nut trees, juniper, live oak, locust, maple, persimmon, pines, salt cedar, sumac, sycamore, wild cherry, willow and many other ornamental plants. Leaves may be damaged by having the outer layer of cells (epidermis) removed by small caterpillars or all tissues but major leaf veins removed by larger caterpillars. Infested plants develop more bagworms each year because female stages do not fly. They may become abundant enough in some years to completely defoliate their host plant. Nearby host plants can remain unaffected. Completely defoliated evergreen species such as arborvitae and juniper, can be killed. During leaf-feeding, the caterpillars emerge from the top of the bag and hang onto the host plant with their legs and sometimes with a silken thread. The bottom of the bag remains open to allow fecal material (frass) to pass out of the bag. During molts and pupation, caterpillars seal the bags. Dispersal of bagworms to new host plants occurs when young caterpillars hanging from silken threads are spread by wind or perhaps by birds. Bags can be removed from host plants by hand. During the winter months, bags contain remains of female moths and eggs produced by them. During the late spring and summer, bags will contain caterpillars that can be removed. Males are best reared from bags after caterpillars pupate. Males can also be attracted to lights. Pest Status: Caterpillar stages in bags feed on leaves and can defoliate shrubs and trees; medically harmless. Several species occur in the state. Management: Hand-pick bags in the winter to eliminate spring populations. If impractical, treat in early spring when the eggs are hatching and definitely before the new bags are less than 1/2 inch long with Bacillus thuringiensis or Spinosad.