“Spongy moth” has been formally adopted as the new common name for the invasive moth species Lymantria dispar by the Entomological Society of America (ESA).

The ESA Governing Board voted unanimously to approve the addition of “spongy moth” to ESA’s Common Names of Insects and Related Organisms List, completing a process started in July 2021 when the previous name, “gypsy moth,” was removed due to its use of a derogatory term for the Romani people. The change is the first undertaken by ESA’s Better Common Names Project. The full press release can be viewed here.

The new name “Spongy moth”— derived from the common name used in France and French-speaking Canada, “spongieuse”— refers to the moth’s sponge-like egg masses, an important target for management efforts to slow the spread of the insect.

Urban Forest Pest Highlight: Spongy Moth

What is it?

Our friends at the Washington Invasive Species Council explain, “Spongy moths include Lymantria dispar asiatica, Lymantria dispar dispar, and other invasive moths including rosy moths (Lymantria mathura) and nun moths (Lymantria monacha). The spongy moth is one of the worst American forest pest insects. It devours the leaves of more than 500 different species of trees and shrubs and causes enormous damage to the environment and the economy.” The spongy moth especially has an appetite for the following tree species: oak, apple, hawthorne, poplar, willow, and maple. While European spongy moths almost exclusively consume deciduous trees, Asian spongy moths also readily consume evergreen trees, which is of great concern for Western Washington. European spongy moths will also consume evergreen trees when an area is infested.

Below are some common characterizes of the insect:

  • Spongy moth adult males are light brown. Lymantria dispar dispar moth females are white with dark zigzags on the wings and do not fly.
  • The spongy moth has a wing span of about 1 1/2 inches.
  • Eggs masses of a hundred or more are laid on branches or other sheltered places. The masses are buff colored when freshly laid and will pale as they age.
  • Mature larvae are covered in light-colored tufted hairs with five pairs of blue bumps followed by six pairs of red bumps down the back.
  • The pupae (or resting stage between the caterpillar larva and adult moth) is a dark brick red and usually found under tree bark and crevices or other protected areas.

Is it in Washington yet?

Spongy moth caterpillar leaf defoliation

Yes, however no permanent population exists due to control efforts. Recent Actions (as described in DNR’s 2021 Forest Health Highlights): The Washington State Department of Agriculture (WSDA) conducted an eradication project for a detection of spongy moth from the subspecies L. dispar asiatica in the spring of 2021 in the Silver Lake area of Cowlitz County. A 634-acre block area was treated with three aerial applications of the bacterial insecticide Bacillis thuringiensis var. kurstaki (Btk). Post-treatment high density delimitation traps were placed in and around the treated area following the Btk application and will continue to be surveyed for three years to ensure the eradication effort was successful. No moths were trapped in this area in 2021.

WSDA deployed roughly 23,000 detection traps for the spongy moth subspecies L. dispar dispar and L. dispar asiatica statewide in 2021. Five (5) adult male moths collected in Kitsap, Pierce, Snohomish, and Whatcom counties in 2021 were identified as L. dispar dispar and one (1) moth collected in a remote area of Stevens County was identified as L. dispar asiatica. WSDA, in conjunction with USDA-APHISPPQ, has determined high density mass trapping and precision delimitation as the best response to the L. dispar asiatica detection in Stevens County. High density trapping will allow WSDA to gather additional data on the location and extent of a possible L. dispar asiatica infestation allowing us to implement an insecticide treatment of the area in the following year if trapping results deem it necessary. No eradication projects are planned for 2022.

The characteristic “spongy” egg masses in a highly infested area.

Why should I care?

Both spongy moth subspecies are a great threat to Washington’s forests and urban landscapes; however, L. dispar asiatica feeds on a wider range of host trees, including conifers, and females are capable of flight, so the risk of rapid spread and severity of damage is higher than with L. dispar dispar.

Due to its voracious appetite and ability to reproduce, the spongy moth causes incredible damage to forests, nurseries, vegetation along creeks and rivers, and trees and shrubs in yards and parks. It also alters wildlife habitat and affects the quality of life in communities that experience repeated outbreaks. The U.S. Department of Agriculture estimates that the economic cost of spongy moths has averaged $30 million a year for the past 20 years, mostly due to quarantines imposed on timber and agricultural products.

How Do We Stop It?

Spongy moths primarily are introduced by people. So, please take precautions when traveling to infested areas to avoid bringing eggs back on your cars, recreation vehicles, and outdoor supplies. Do not remove or vandalize traps and follow quarantine rules and do not transport any firewood or other outdoor material from infested areas. Report a sighting if you see anything suspicious!

Please visit WSDA’s Spongy Moth Frequently Asked Questions page for more information.


Washington Invasive Species Council

Washington State Department of Agriculture