The Garden recognizes that the common names of species like gypsy moth are derogatory. Until a new common name is selected for this species, we will refer to it only by its scientific name: Lymantria dispar. For more details, see this July 12, 2021 posting by the Entomological Society of America.
More than 300 species of trees and shrubs, particularly oak (Quercus), apple (Malus), linden (Tilia), birch (Betula), hawthorn (Crataegus), aspen (Populus) and alder (Alnus)
Description & Symptoms
Lymantria dispar moths are a serious pest of forest and urban trees. Newly hatched larvae chew tiny holes in leaves in spring. Later in the season, mature larvae skeletonize leaves, and in severe cases, entirely defoliate trees. Larvae generally feed at night, hiding during the day in bark crevices or leaf litter on the ground.
Lymantria dispar moths can be observed in all four developmental stages: egg mass, larva (caterpillar), pupa and adult moth. The egg mass is about 1½ inches long and ¾ inch wide with a buff or tan fuzzy surface. Mature larvae are about 2½ inches long, hairy, with five pairs of raised blue spots and six pairs of raised red spots. The immobile pupa is reddish-brown, leathery, and about 1½ inches long. Female moths are white or cream-colored with black markings on the wings and a wingspan of about 2½ inches. Despite their large wingspan, females cannot fly. Male moths are brown, also with black markings, and a smaller wingspan of about 1½ inches.
Timing & Life Cycle
By far the longest period in the Lymantria dispar moth life cycle is the egg mass stage. Female moths lay eggs from late July to early August on almost any sheltered surface — bark crevices, rocks, picnic tables, vehicles. Egg masses, each containing 100 to 1,000 eggs, overwinter and hatch into tiny larvae the following spring, usually in early May in the Chicago region. These larvae crawl or are blown on silk strands to the leaves of trees, where they begin to feed. The larvae go through several growth stages, eating increasingly voraciously as they get larger. By late June or early July, the fully grown larvae pupate and enter a two-week inactive stage before emerging as adult moths in late July. The moths mate, lay their eggs, and then die.
When present in high numbers, Lymantria dispar moths are a serious leaf-eating pest of hardwood trees. Severe infestations can defoliate trees, leaving them vulnerable to other insect pests, diseases, and cultural stresses. Repeated attacks over several years may kill a tree. However, healthy deciduous trees generally survive and grow a new set of leaves after being defoliated. Where moth populations are low, damage to trees often is minor and not harmful.
Treatment & Solutions
Control of Lymantria dispar moths is handled by local, state, and federal agencies, which are monitoring the spread of the moth into the Midwest from the Northeast. Homeowners can assist by searching their property for egg masses or any other signs of Lymantria dispar moths. If you live outside a quarantined area and find any evidence of the moth, call the Illinois Department of Agriculture’s toll-free Lymantria dispar Moth Hotline at
(866) 296-6684 for specific instructions.
In Lake County, currently the only county in Illinois under quarantine, egg masses should be scraped directly into a plastic bag, sealed, and thrown away. Tree wraps can be used to capture migrating larvae on tree trunks. Applications of biological and chemical treatments should be made only by pest control professionals.
Some tree species are less likely to be attacked by Lymantria dispar moths. These include ash (Fraxinus), dogwood (Cornus), holly (Ilex), sycamore (Platanus), tuliptree (Liriodendron) and catalpa (Catalpa). Maintaining the health and vigor of existing trees with good cultural practices helps trees withstand an infestation of Lymantria dispar moths.
For more information about Lymantria dispar moths, call the Plant Information hotline at (847) 835-0972.