Common Name: Fall webworm
Scientific Name: Hyphantria cunea (Drury)
Description: Webs can cover leaves, clusters of leaves or leaves on whole branches, becoming several feet in diameter. They contain many hairy caterpillars that hatched from one egg mass. Some trees can have a high number of webs. Caterpillars grow to about 1 inch long, with black or reddish heads, pale yellow or greenish bodies marked with a broad mottled stripe containing two rows of black bumps (tubercles) down the back (one pair on each body segment) and yellowish patterns on the sides. They are covered with tufts of long whitish hairs. Adult moths are mostly white with dark spots on the wings.
Webs of fall webworms are often confused with other caterpillar-produced webbing in trees. Webs produced by eastern tent caterpillars, Malacosoma americanum (Fabricius) (Lepidoptera: Lasiocampidae) are constructed in crotches of trees, and caterpillars leave the nest to feed on leaves. Another web-producing caterpillar is the genista caterpillar, Uresiphita (=Tholeria) reversalis (Guenee) (Lepidoptera: Pyralidae), commonly found on Texas mountain laurel. Caterpillars of this and other web-producing species are less hairy and lack the double row
of black dots on the top of each body segment characteristic of the fall webworm. Fall webworms are also sometimes called “bagworms,” but this term is more accurately used for true bagworms (Lepidoptera: Psychidae).
Life Cycle: Winter is spent in the pupal stage in a silken cocoon in leaf litter or in cracks on rough bark. Adults emerge in spring after host plants have developed leaves and mate. On the underside of leaves female moths deposit eggs in masses that appear covered with hair. Caterpillars hatch and begin feeding on leaves, spinning silken webs enveloping their feeding sites. Caterpillars molt up to eleven times through growth stages (instars) before leaving the web to pupate. Two to four generations occur per year, depending on locality within Texas.
Habitat and Food Source(s): Caterpillars have chewing mouthparts. Adults have siphoning mouths. Caterpillars will feed on leaves of a large number of trees including hickory, mulberry, oak, pecan, poplar, redbud, sweetgum, willow and many other shade, ornamental, fruit and nut trees. Preferences for different host plant species appear to be regional and seasonal. They feed on tender parts of leaves, leaving the larger veins and midrib. Webworms can appear as early as April in south Texas and high numbers of webs can occur during any of the generations that occur through the summer. However, the last generation is generally the most damaging. Adults are attracted to lights.
Pest Status, Damage: Caterpillars produce loose webbing around leaves and branches in which they feed on leaves; produce unsightly “nests” and cause loss of leaves and some plant stress; hairs on larvae may cause skin irritation.
Literature: Johnson & Lyon 1988; Robinson & Hamman 1980.