Spongy Moth caterpillar on a leaf

Spongy moth caterpillar with the characteristic pattern of blue and red pairs of spots along its back.
Photo: Karla Salp, Washington State Department of Agriculture, Bugwood.org

Updated: September 4, 2026

The common name of Gypsy moth (Lymantria dispar) was officially changed to spongy moth.

Key points

  • Spongy moth, native to Europe, was introduced and accidentally released in Massachusetts in 1869.
  • This species is a serious threat to oak trees, and is considered a major forest pest. The first significant infestation in Maryland dates back to the 1980s.
  • Predators, parasites, and diseases attack spongy moth caterpillars, but the Maryland Department of Agriculture (MDA) continues to survey for this pest to monitor populations. Areas with high populations are treated in cooperation with the USDA Forest Service, MDA, local county governments, or landowners. For details, visit the MDA's website: Spongy Moth Cooperative Suppression Program.
  • Spongy moth caterpillars feed in May and June. They prefer oak (Quercus), but will also feed on sweetgum (Liquidambar), linden (Tilia), willow (Salix), birch (Betula), apple (Malus), alder (Alnus), boxelder (Acer negundo), hawthorn (Crataegus), and Colorado spruce (Picea pungens). A large caterpillar population can defoliate acres of trees.
  • Deciduous trees suffering more than 50% defoliation for two consecutive years will be significantly weakened and may die.

Spongy moth identification and life cycle

A creamy-white moth perched on a tree limb next to several felted tan-brown egg masses attached to the bark.
A female spongy moth perched next to egg masses on the bark of a tree branch.
Photo: Karla Salp, Washington State Department of Agriculture, Bugwood.org
  • Eggs: The oval-shaped egg masses are felted-looking, tan in color, and about 1½ inches long. They are laid in bark crevices, on the undersides of branches, on the ground under loose stones, or on boards, firewood, lawn furniture, campers, and in many other places. Egg hatch begins in late April or early May, depending on the temperature.
  • Larva: Young caterpillars are black, hairy, and only one-sixteenth of an inch long. As they grow, caterpillars change color, and by the third instar (development stage), they are about five-eights of an inch long and have 10 blue spots down their backs. Caterpillars grow up to 2 or 2½ inches in length, and at that point have 5 pairs of blue dots and 6 pairs of red dots on their backs.
  • Pupa: Smooth, teardrop-shaped, and dark brown, about 1 inch long. They are not surrounded by a cocoon. Pupae may be found attached to just about anything around the outside of the home, including tree trunks, cars, trailers, around door frames, on the siding overhang above the foundation, and in many other protected locations.
  • Adult: Female moths have white wings with small dark markings. The wingspan is 2 inches (the distance between wingtips when the wings are held out to the sides, not over the back). Male moths are brown with black markings. Adult moths emerge and are active from late June to late July.

Life cycle chart

The following bar chart illustrates the life stages of spongy moth throughout the year. From about late June (at the earliest) through early May (at the latest) of the following year, egg masses can be present. The larvae (caterpillars) are present between mid-April (at the earliest) and early July (at the latest). Pupae are present from about late June into the end of July. Adults are active from July into about mid-August.

illustration of gypsy moth life cycle
From University of Maryland fact sheet 242, "The Gypsy Moth and the Homeowner" by Michael Raupp, John A. Davidson, and F.E. Wood
A brownish-cream-colored moth with scattered, small black wing spots rests on a plant stem.
An adult spongy moth. Photo: Karla Salp, Washington State Department of Agriculture, Bugwood.org
Three dark brown pupae loosely attached with silk to tree bark. There are sparse golden-brown bristly hairs clinging to the pupae.
Three spongy moth pupae loosely attached to tree bark with strands of silk. A few short golden-brown body hairs from the shed caterpillar skin are sparsely sticking to the pupae.
Photo: Ferenc Lakatos, University of Sopron, Bugwood.org
Small, black, rounded pellets scattered on bare soil.
A buildup of dark, pellet-like caterpillar frass (poop) on the ground can be an initial sign that a population of spongy moth is in a tree's canopy. Photo: Karla Salp, Washington State Department of Agriculture, Bugwood.org

Behavior and feeding damage

A tall tree canopy, viewed from the ground, with a large region of sparse foliage due to caterpillar feeding.
Accumulated spongy moth feeding damage can defoliate tree canopies. Photo: Ferenc Lakatos, University of Sopron, Bugwood.org
  • Spongy moth caterpillars do not spin webs or make silken nests in trees, unlike tent caterpillars and webworms.
  • Very young caterpillars are carried by the wind from tree to tree. Young caterpillars spend most of their time in the treetops feeding. Their chewing damage looks like "shot holes" in the leaves (scattered small holes), and is not easily visible from the ground.
  • Larger caterpillars can consume entire leaves to the midrib (central leaf vein), causing prominent defoliation when they are abundant. Late-stage caterpillars are responsible for most of the leaf loss in trees, and are more difficult to control with pesticides than young caterpillars.
  • When the caterpillars are finished feeding, they migrate out of the trees in search of hiding places to pupate.
  • Female moths do not fly. Male moths do fly, and are one of the few daytime-flying moths found in Maryland.
  • The adult moths do not feed — they only live a short time, during which they mate and the female lays eggs in masses.
  • There is one generation per year, and winter is spent in the egg stage.

Management for spongy moth

  • Remove egg masses off of trees or other structures before April (when egg hatching begins). Scrape the eggs into a container for disposal, or into a jar filled with soapy water. To reduce the risk of allergic reactions to the moth body hairs covering the egg masses (the substance that makes them look felted), wear gloves and be careful not to inhale the hairs dislodged when scraping them off.
  • Use hiding bands to provide a refuge for migrating caterpillars which can then be removed and destroyed.
  • Insecticide products using the active ingredient Bt (Bacillus thuringiensis, specifically strains aizawai and kurstaki) will control young caterpillars early in the spongy moth life cycle. The active ingredient spinosad will kill both small and larger caterpillars, but must be thoroughly and evenly applied to the entire plant to work well. Large-statured plants should be treated by a certified pesticide applicator. (Many landscaping company employees and arborists have this license, or work under the supervision of a license-holder.)
An orange-colored wasp stands over a spongy moth caterpillar on a leaf. The wasp is about half the size of the caterpillar in body length.
A beneficial, parasitic species of braconid wasp attacks a spongy moth caterpillar.
Photo: Scott Bauer, USDA Agricultural Research Service, Bugwood.org
A limp caterpillar, hanging by a couple of its feet in an upside-down V shape, on tree bark.
A spongy moth caterpillar killed by nuclear polyhedrosis virus, in the characteristic upside-down V shape (limp and hanging by a couple of its legs).
Photo: Steven Katovich, Bugwood.org
A red- and blue-spotted caterpillar sits on top of a cluster of small white cocoons on a background of tree bark.
A parasitized spongy moth caterpillar sitting on top of a cluster of cocoons made by the parasites after the larvae left its body.
Photo: Ferenc Lakatos, University of Sopron, Bugwood.org
An aerial view of forest on a mountain foothill with a large swath of leafless trees surrounded by a mix of leafy and leafless trees.
Spongy moth outbreaks can cause heavy defoliation in forests.
Photo: Mark Robinson, USDA Forest Service, Bugwood.org

Additional resources

The Spongy Moth and the Homeowner | University of Maryland Extension fact sheet

Spongy Moth | Maryland Biodiversity Project