The Spongy Moth (Lymantria dispar) has a four-stage life cycle, and its appearance changes dramatically throughout the year. Although often searched for as the “gypsy moth,” the official common name has been updated to Spongy Moth. Understanding the visual distinctions of each stage is key for accurate identification and monitoring.
Identifying the Larval Stage (Caterpillar)
The larval stage is the most easily recognized and distinctive phase of the Spongy Moth’s life. When fully grown, the caterpillar reaches 1.5 to 2.5 inches (38 to 63 millimeters) in length. Its body is dark brown or black, covered with numerous fine, protective bristles.
The most identifying feature is the unique pattern of raised, colored bumps, called tubercles, running in two rows down its back. The caterpillar displays five pairs of blue spots toward the head, followed by six pairs of brick-red spots extending toward the rear. This sequence of blue and red tubercles is the definitive feature for identification.
The head capsule is typically a bright yellow or yellowish-orange color, sometimes flecked with black markings. Early-stage caterpillars are smaller, darker, and fuzzier, sometimes appearing nearly black, but they eventually develop the characteristic spot pattern as they grow. The overall hairy appearance makes the larva a prominent sight during late spring and early summer feeding periods.
Distinguishing Adult Moths (Male vs. Female)
The adult stage exhibits significant sexual dimorphism. The female moth is noticeably larger and heavier-bodied, possessing a wingspan that can reach up to 2.5 to 3.5 inches (63 to 89 millimeters). Her wings are predominantly creamy white or pale yellowish-white, marked with faint, dark, wavy lines.
The female moth is flightless despite having fully formed wings. She is often observed resting on tree trunks or other surfaces near where she emerged. Her antennae are thin and threadlike, lacking the prominent feathering seen on the male.
In contrast, the male moth is smaller and more slender, with a wingspan of about 1 to 1.5 inches (25 to 38 millimeters). The male is a capable and erratic flier, often seen flying during the day. His wings are a darker, mottled gray-brown, often with dark, wavy markings. The male’s antennae are highly feathery (pectinate), which helps him detect the female’s pheromones from a distance.
Appearance of Non-Mobile Stages (Egg Mass and Pupae)
The egg mass and the pupa are the two non-mobile stages. The egg mass is the overwintering stage, typically laid in late summer and remaining present until the following spring. These masses are distinctive, appearing as an irregularly shaped, soft, felt-like patch.
The mass is covered with tiny hairs, or scales, shed from the female’s abdomen, which gives it a spongy texture. The color ranges from buff or tan to a light brown. They are usually about 1.5 inches long and can be found on any outdoor object, including tree trunks, rocks, or lawn furniture.
The pupa is the stage between the caterpillar and the adult moth, typically found in sheltered areas or crevices on trees. This casing is a dark reddish-brown color, appearing leathery and hard. Pupae are often covered in small hairs and are sometimes loosely attached to a substrate with silk threads. Female pupae are larger than males, and they generally resemble a teardrop shape.