Spongy Moths (formerly known as Gypsy Moths)

March 2022: The Gypsy Moth (Lymantria dispar) has been renamed by the Entomological Society of America as the Spongy Moth. The new name refers to the moth's sponge-like egg masses. Read more here.

A member of the order Lepidoptera, the North American and European Spongy Moth (Lymantria dispar) is one of the most destructive hardwood tree pests in the Eastern United States. Introduced in Massachusetts in the mid-1800's to create a silkworm industry in the United States, Spongy Moths became a pest in the region within a decade of introduction. The damage caused by the larvae devastated trees in the northeast and some accounts recalled the caterpillars "raining down" on residents in towns as they drifted in the wind. The spread of Spongy Moths is naturally slow, but accidental transportation of the eggs has resulted in numerous isolated regions where Spongy Moths are prevalent. One way to help slow their spread is to buy locally sourced firewood (within 50 miles of cutting is preferred).

Life Cycle & Identification:

Spongy Moth eggs are laid in clusters of 500 to 1,000 eggs during the adult mating season (mid-July through August) and are distributed throughout a felt-like mat of hair that is light tan in color. The egg clusters are usually 3/4 to 1 ½ inches in length and are often found attached to tree trunks and branches that provide shelter. Since the eggs overwinter, mortality rates vary depending on what part of the tree they are laid and climatic factors such as temperature and precipitation.

Spongy Moth caterpillars emerge from eggs during late spring (usually late April) and measure roughly 1/4 inch long and are dark brown to black in color. After they emerge they spin silk and drop from branches and leaves to disperse as the wind blows. The caterpillars destroy vast amounts of foliage as they feed, preferring leaves of deciduous hardwood trees; however, Spongy Moth caterpillars will move to other hardwood trees when competition for food grows. The caterpillars typically molt five and six times for males and females respectively and reach 2 ½ inches in length with dark brown to black coloration. The distinguishing traits of Spongy moth caterpillars when compared to other species are the five pairs of blue spots near the head and six pairs of red spots towards the tail. After molting, the caterpillars must pupate to reach adulthood.

Both male and female Spongy Moths appear in mid-summer and are easily distinguished from one another with the males brownish-gray in color while the females being slightly larger in size and white in color with scattered, black markings. Early identification is key to any integrated pest management control of Spongy Moths.

Controlling Spongy Moths:

Early identification is imperative for successful control of Spongy Moths. Trapping helps identify the moths and monitor their spread to new regions. Traps are specific in shape and require that a pheromone be used as an attractant.
Physical controls like sharp blasts of water and physical wiping of the egg masses can be used to remove them. Tree banding after eggs have hatched reduces Spongy Moth caterpillar's ability to reach foliage and can drastically reduce damage symptoms. This is done by wrapping either burlap folded over itself or tape with adhesive applied around the tree trunk
Introduce Trichogramma Wasps as moth egg parasites early in the spring to help reduce egg populations. This can be effective to reduce the number of damaging caterpillars hatching, but should not be relied upon for full control.
Spray Horticultural or Dormant Oils onto egg masses where visible in the fall and winter to reduce hatch rates during the following season.
Maintain proper watering and feeding schedules for target trees to boost the trees' resistance to pests and reduce the number of eggs being laid.
Insecticidal sprays containing Btk sprays are most effective against young caterpillars as older ones tend to be more resistant to the bacillus.

Related Information: