Spongy Moth

Scientific Name: Lymantria dispar
Formerly known as: Gypsy Moth
Damages: Forests and Trees
Categories: Invasive

Similar Species

  • Eastern tent caterpillar
    (Hyphantria cunea)
  • Fall webworm moth
    (Malacosoma americanum)

  • (Lymantria dispar asiatica)

Over one hundred years ago, spongy moth caterpillars were brought into the U.S. for research as a possible source for silk production. Escapees found a welcoming habitat, and masses of caterpillars have been plaguing our forests and landscapes on and off for over a century.

What Do Spongy Moths Look Like?

white fuzzy moth with black markings and a fuzzy brown mass under its wings.

Adult spongy moth females are white with brown markings that resemble an inverted V pointing toward the head.

gray brown triangular moth with fuzzy antennae and black markings

Males are brownish with black markings and have a wingspan of 1 to 1 1/4 inches (25-32mm) - these are the ones you’ll see flying.

tan spongy lumps on the side of a tree

Dark brown masses of 100 to 600 eggs protected by a light-colored, almost hairy covering.

hundreds of tiny black and brown caterpillars on a fuzzy light brown lump

Early instar larvae are small, dark brown-to-black, and very fuzzy.

hairy caterpillar eating a leaf

Later instars lighten in color and have a showy display of two rows of colored spots: five pairs of blue and six pairs of red.

brown hairy pupae hanging from a tree

The dark brown, hairy pupae are about 2 inches long.

Life Cycle and Behavior

Eggs

In July and August, females lay dark brown masses of 100 to 600 eggs protected by a light-colored, almost hairy covering. The older the mass, the softer they are to the touch. They are often on tree trunks, but can be found on the side of buildings, signs, trailers, are other outdoor surfaces.

Caterpillars

The following spring, ¼ inch (6.3mm) long hatchling caterpillars move away from the egg mass to feed on leaves. To do so, they often produce silken threads that catch in the wind and send them aloft to other trees—a practice called ‘ballooning’ that enables their spread. 

  • Early instar larvae are small, dark brown-to-black, and very fuzzy. 
  • Later instars lighten in color and have a showy display of two rows of colored spots: five pairs of blue and six pairs of red.
  •  At about seven weeks, larvae are fully grown at 2 – 2 1/4 inches long (50-56 mm).

Pupae

In June and early July, larvae pupate in hiding spots under bark or similar protection. The dark brown, hairy pupae are about 2 inches long.

Adults

Males—Once they complete pupation, adult male spongy moths emerge and fly erratically during the daytime in search of mates. 
Females—Heavy-bodied adult females have wings but don’t fly. They rest on trees and wait as males follow female pheromone trails to find them.

Why do I have Spongy Moths?

Spongy moths are an invasive exotic pest with a broad diet. If you have the following preferred plants, your property becomes that welcoming habitat for egg laying and subsequent feeding of plant leaves by masses of Spongy moth larvae. Selecting Disease and Insect Resistant Ornamental Plants with spongy moth in mind can help.

Spongy moths are attracted to oak, willow, apple, crabapple, white birch, witch hazel, mountain ash, basswood, linden, pine, Douglas-fir and spruce.

If preferred plants aren’t available spongy moths will feed on hardwoods (maple, cherry, walnut, hickory and chestnut) and hemlock, elm, hackberry, yellow birch, beech, cottonwood, box elder, and ironwood.

Spongy Moths generally avoid ash, balsam fir, locust, Scotch pine, red cedar, tulip poplar, catalpa, sycamore, and dogwood.

Should I Worry About Spongy Moths?

It's a good idea to wear gloves when coming in contact with spongy moth caterpillars. The tiny hairs (setae) of spongy moth caterpillars carry histamines that can cause an itchy, red rash in some individuals. 

Tree Health

A healthy tree can withstand some defoliation, finding spongy moths on your property is serious but not necessarily the end for affected trees. Two factors must be considered—the number of larvae, and whether this is a repeated defoliation from a prior year. 

If you’ve noticed defoliation on trees in your landscape, don’t worry. They often will bounce back and put out new growth after the spongy moth caterpillars have stopped feeding for the season.

To help these stressed trees rebound, it can be beneficial to water the trees if there are dry spells over the summer.

Scouting to Assess Risk

Management of spongy moths using IPM always requires scouting. Take a good look at your trees, take photos, and make note of your findings to see if numbers are getting higher and damage worse.
Spongy moth outbreaks are naturally reduced by birds, rodents, parasites, and diseases. What looks like a problem in one year does not indicate the same problem will occur the following year. It is typical, in fact, to see an outbreak build for a year or two only to have the population collapse due to spongy moth diseases in a subsequent year. 
 

Getting Rid of Spongy Moths

Manual Removal

It's a good idea to wear gloves when coming in contact with spongy moth caterpillars. The tiny hairs (setae) of spongy moth caterpillars carry histamines that can cause an itchy, red rash in some individuals. 

Burlap Cloth Flap Trap

You may want to protect individual trees by using a simple burlap cloth flap trap. This involves encircling a tree with a foot-wide length of burlap tied with twine right in the middle and pulling the top portion over the lower portion. This technique takes advantage of the caterpillar’s drive to crawl upwards and not turn around if they encounter the barrier of the burlap. The accumulated caterpillars can be periodically removed and destroyed.

Remove Caterpillars and Adult Moths

During the summer, look for caterpillars and adult moths. Squish them or knock them into soapy water. (Note—some people have an allergic reaction when coming in contact with spongy moth caterpillars so it's a good idea to wear gloves.) During outbreaks, high numbers make this impractical. Take notes of what you find.

Leave Diseased Larvae

Spongy moth larvae are affected by a viral disease and fungal infections. If you find diseased larvae, leave them be so that other larvae will also be infected. Larvae killed by viruses look like V's. Larvae killed by fungi hang head down.

Find and Remove Egg Masses

If you’ve seen spongy moth caterpillars or defoliation during the growing season, consider going out on a dry day between September and late April to look for egg masses on trunks. Scrape any you find into soapy water.

Chemical Control

If your scouting confirms high concentrations of spongy moth caterpillars, a decline in tree health, or threats to maple sap production, insecticide sprays may be an option. There are two kinds of pesticides: traditional chemical sprays or biological sprays containing naturally occurring organisms.

Biological Sprays

The most common biological used on caterpillars is Bacillus thuringiensis kurtaki (Btk). Bt is most effective on small caterpillars, and harmless to people, animals, and plants. By introducing it into their digestive tract, caterpillars become paralyzed and are unable to feed.

Note: Bt affects other young moth and butterfly larvae, too.

Traditional Insecticides

Traditional insecticides can impact many insects including beneficial, native insects (such as bees).

  • Always use, or allow their use, only when necessary and follow all pesticide label instructions.
  • Hire professional pesticide applicators trained to legally and correctly use registered products. Because of the area involved—including height of tree—pesticide spraying is a job best left to trained professionals with the proper equipment. However, a well-informed homeowner can apply certain products in some instances. Note: spraying is not effective against pupae, egg masses, or caterpillars over one inch in length.
  • Contact your local cooperative extension if you have questions about what a proposed pesticide applicator is telling you and never agree to unnecessary applications.
portrait of Brian Eshenhaur
Brian Eshenaur

Senior Extension Associate

NYS Integrated Pest Management

Brian Eshenaur