Fall webworm: what the agencies record

This page describes what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. The fall webworm (Hyphantria cunea) is native to North America, and none of the three pages read lists it as regulated or notifiable. Each section names its source, all read on October 8, 2026. The parent page, insect pests of trees, compares it with the other pests on the list.

Names

Natural Resources Canada, called NRCan, gives the scientific name Hyphantria cunea (Drury) and the French name chenille a tente estivale. It places the insect in the order Lepidoptera, the moths and butterflies. Penn State Extension and Clemson Extension use the common name fall webworm.

What the sources say to look for

NRCan says the insect is easily detected by numerous silk webs on crown branches in summer. The larvae feed on foliage throughout their development and enlarge the web as they grow, so that it can sometimes enclose the entire tree. Penn State says the large, conspicuous webs contain caterpillars, dead partially eaten leaves and droppings, and that the web is built over the end of a branch rather than at the crotches where the eastern tent caterpillar builds. It says webs may surround 2 to 3 feet of branch and that remains of nests may persist through winter.

Clemson says that young larvae feed on one side of the leaf, which it calls skeletonizing, larger larvae eat all but the leaf veins, and that both kinds of leaf are found inside the web. It says the caterpillars have fine hairs that can be irritating to some people. Penn State describes the caterpillars as usually greenish with a broad dusky stripe along the back and a yellow stripe along the side, and the adults as ranging from pure white to white with black spots.

Hosts

The three sources give different counts. NRCan says the insect attacks over 100 species of trees on the continent, and its main host list includes apple, balsam poplar, choke cherry, pin cherry, speckled alder, trembling aspen, white ash, white birch, white elm and willow. Penn State says almost 90 species of deciduous trees, commonly hickory, walnut, birch, cherry and crabapple. Clemson says it has been recorded feeding on over 300 hardwood tree and shrub species, with pecan, hickory, walnut, persimmon, maple and sweetgum the most common hosts in the eastern United States. Clemson adds that the amount of foliage on a tree and how common a species is in an area also play a part in which trees are attacked.

Life cycle as the sources state it

The sources agree that the insect overwinters as a pupa in a cocoon. Penn State places the cocoon in ground litter, cracks and crevices, or soil, and Clemson also lists bark crevices. Females lay egg masses on the underside of leaves, and NRCan says the female covers them with white hairs from her abdomen. Clemson says the caterpillars are gregarious, feeding together, and that each web is likely made up of caterpillars from one egg mass. Penn State says mature larvae leave the web and pupate on or in the soil.

The number of generations depends on the place. NRCan gives one generation per year in Canada, the northernmost part of the range. Penn State gives one or two a year depending on location in Pennsylvania, and says adults first appear in mid-June. Clemson gives 2 to 5 generations per year in the southern United States.

Where it is reported

NRCan says fall webworm outbreaks occur more frequently in eastern and central North America, and records four infestations between 1939 and 1975 that affected every eastern Canadian province except Newfoundland. It also describes the fall webworm as a rare example of a North American insect that reached Europe and Asia by accident. Penn State calls it a widely distributed native pest, and Clemson says it can defoliate trees in rural and urban landscapes throughout South Carolina.

Damage as the sources describe it

NRCan says the damage occurs near the end of the annual growing season, and that weakened trees may then be easier targets for other insects or diseases. Penn State says the larvae may defoliate a tree occasionally and that on shade trees webs usually occur on occasional branches and reduce ornamental value. Clemson says that in most cases defoliation is limited to a branch or two, and that in smaller trees complete defoliation may occur if the whole tree is covered in webbing. It says no significant damage to forests or natural areas has been reported, while urban and orchard landscapes show stronger effects.

Regulated status and reporting

None of the three pages names a regulation, quarantine order or report line for the fall webworm. For the agencies that take reports of regulated pests, see the guides on reporting a pest in Canada and the United States.

Management as the sources list it

NRCan lists cutting out and burning the branches and leaves bearing nests while the larvae are still young. Penn State lists natural enemies, including birds, insect predators and parasitoids, and pruning and destroying webbed branches within reach. Clemson lists scouting, removing affected limbs, knocking down or tearing open a web, and natural enemies, and says mass trapping with pheromones or mating disruption in orchards is costly and suited to small isolated areas. Penn State also mentions registered insecticides aimed at the webs when they are small. This page gives no product names, rates or timings. For who may apply pesticides, see pesticide licences.