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Pest Information

Fall Webworm

Fall Webworm

  • Latin Name: Hyphantria cunea
  • Common Name: Fall Webworm
  • Other Names: N/A

Pest Details

Fall Webworm
Fall Webworm
Fall Webworm

Origin:

This species is native to North America, but in the 1940’s was accidentally introduced to Europe, eventually spreading throughout Europe and east into much of northeastern Asia. In North America it is found throughout the U.S., much of Canada, and south into Mexico.

Biology:

The moth overwinters as a pupa within a silk cocoon that is hidden under loose edges of bark. The adult moth emerges in the spring with warm weather, usually as early as March in southern regions and May in northern regions. Females then deposit a mass of up to 1,500 eggs on the underside of a leaf on the host tree, covering the eggs with hairs from her abdomen. The larvae undergo as many as 11 molts before maturity and spin small webs around themselves as they feed. In heavy infestations these webs from all the larvae may ultimately enclose an entire tree. When mature the larvae often leave the host tree and wander over the ground and other surfaces nearby, often pupating on surfaces around the tree during warm season generations. They feed on a wide variety of deciduous trees including ash, hickory, oak, maple, poplar, willow, walnut, and others. In cooler regions there may be 1 generation per year but up to 4 generations in warm southern areas where the adult moths may be active year-round. When disturbed the larvae on a tree participate in unison in a defensive movement where they rapidly jerk the front of their body around.

Identification:

The adult moth is either pure white or white and heavily speckled with black spots arranged as broken rows running across the forewings. The wingspan is under 2 inches across. The larva is typical of this family, with a densely hairy body. Two races of this moth occur, with the larvae of one race white to yellowish white with a pair of black tubercles on each segment on top and a black head. The second, the red headed race, is tan with orange tubercles.

Characteristicts Important to Control:

The use of chemical sprays is often necessary to kill the larvae, including both synthetic insecticides as well as natural materials such as Bacillus thuringiensis. Sprays should be directed onto the larvae and their silk web nests, with only a light application needed rather than attempting to remove the webbing with a strong spray. Light infestations will rarely cause harm to a tree and spraying may not be called for.

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