Spongy moth: 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. Each section names its source, all read on October 9, 2026. Quarantine rules are set out country by country on the spongy moth regulated status page, and the moth has a row in insect pests of trees.

Names

The Canadian Food Inspection Agency, called CFIA, says that from 2022 spongy moth is the common name for Lymantria dispar dispar, which was earlier called European gypsy moth, EGM or LDD moth, and that the French name did not change. Forest Research, which writes for the United Kingdom, titles its page gypsy moth, Lymantria dispar. USDA APHIS and The Morton Arboretum use spongy moth. Wisconsin DNR says the insect was introduced into Massachusetts in 1869, and the Arboretum gives the same year for introduction into the United States.

Hosts

APHIS and Wisconsin DNR both say the caterpillars feed on more than 300 species of trees and shrubs. Forest Research says the caterpillars feed on a variety of broadleaved trees and shrubs, preferring oaks and poplars in forests, and also take small garden trees and shrubs including ornamental conifers, with beech hedges a frequent target. The Arboretum calls it a general feeder, with oaks preferred when numbers are low. It lists alder, apple, aspen, birch, hawthorn, larch and linden as susceptible, and says early-stage caterpillars do not feed on beech, dogwood, elm, hemlock, maple, pine, Prunus species, serviceberry, spruce or walnut. It lists tulip tree, tupelo, arborvitae, ash, black locust, fir, holly, juniper, redbud and sycamore as trees the caterpillars almost never feed on.

Life cycle as the sources state it

Forest Research and the Arboretum both give one generation a year, overwintering as eggs. Forest Research says the eggs are laid in plaques 3 to 4 cm long covered in yellowish-brown hairs from the female, holding between 50 and 800 eggs, and that new eggs are bright yellow and firm while hatched eggs in spring are soft and spongy. It places hatching in April and May in the United Kingdom, says newly hatched larvae are about 2 mm long and balloon away on silk threads in the wind, and says larvae are usually fully grown by June at up to 70 mm. Pupation takes 10 to 14 days and adults usually emerge in July. The females have reduced wings, are largely flightless and attract males with a pheromone.

The Arboretum, writing for northern Illinois, gives up to 1,000 eggs in a mass about 1 1/2 inches long, hatching usually in May, pupation from about mid-June and adult males emerging in early July. It says females lay under loose bark, in woodpiles, on outdoor furniture or in any concealed spot, and that the adults do not feed. APHIS gives mature caterpillars as 1.5 to 2.5 inches and describes the female as nearly white with a 2-inch wingspan that does not fly, and the male as brown with a 1.5-inch wingspan that can.

What the sources list as signs

Forest Research and the Arboretum both describe a mark on the caterpillar: five pairs of blue spots followed by six pairs of red spots along the back, which Forest Research calls an easy way to tell it from similar species. CFIA lists chewed holes in leaves, whole leaves eaten, and egg masses on trunks and branches that can be seen in late July. The Arboretum says caterpillars feed in groups and rest on branches and trunks by day, and that they make no tents or webs. APHIS lists egg masses on trees and outdoor items, caterpillars, adults and defoliated trees, and says heavily infested forests can look barren in midsummer.

Damage and health notes

Wisconsin DNR says outbreaks come about every 10 to 12 years and last 2 to 3 years, that healthy trees are likely to survive defoliation, and that the caterpillars' hairs can set off skin rashes or other reactions in some people. The Arboretum says trees are rarely killed unless already weakened, but that consecutive years of defoliation leave them open to insect and disease problems, and that more than 13 million acres of woodland were defoliated in one season. Forest Research says damage is most severe on small trees, that a host usually recovers, and that repeated infestations can eventually kill a tree. It says the hairs do not cause the severe effects that oak processionary moth hairs do, though like all hairy caterpillars they are potential allergens.

Where the agencies record it

APHIS, on a page modified September 17, 2026, lists 20 states and the District of Columbia, which are named on the spongy moth regulated status page. It also says all states are at high risk. CFIA, on a page modified December 10, 2025, says it is found in Quebec, Ontario, New Brunswick, Nova Scotia and Prince Edward Island, has been detected in British Columbia, where the province is carrying out eradication, and was detected and eradicated in Alberta, Saskatchewan and Manitoba. Forest Research says it is found throughout much of London and patchily in the south-east of England, and is native to parts of continental Europe. Wisconsin DNR says life stages began turning up in the state in the late 1960s, and the first noticeable defoliation was in Oconto County in 1997.

Status and reporting

Forest Research says the moth is present in the United Kingdom and not notifiable, with no statutory requirement to tell the plant health authorities, though serious damage can be sent through its TreeAlert tool. CFIA asks for reports from British Columbia, Alberta, Saskatchewan, Manitoba and Newfoundland and Labrador. APHIS names State plant regulatory officials and State plant health directors, and Wisconsin DNR gives a state line for non-quarantined counties. See report a pest in the United States, Canada and the United Kingdom. This page gives no product names, rates or timings for any treatment.

Text on the United Kingdom is adapted from Forest Research and contains public sector information licensed under the Open Government Licence v3.0.