Spongy Moth

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No quarantines at this time

Pest Profile

The spongy moth (SM) is a pest that voraciously feeds on the leaves of trees and shrubs, threatening residential settings, forests and agricultural tree crops.

Adult Spongy Moth (Photo Credit: Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org)

This website has been designed to answer questions about this pest. The spongy moth is originally from Europe and Asia. It was brought to the U.S. for breeding experiments in Massachusetts in the 1860's and accidentally escaped.

It has since moved steadily southward and westward,

and now occupies the northeastern U.S. from Maine to Virginia and westward to Wisconsin. Spongy moth caterpillars feed on hundreds of kinds of plants and are capable of defoliating trees at an alarming rate. A single spongy moth caterpillar can eat up to one square foot of leaves per day. In the northeastern United States, millions of these caterpillars emerge each spring and devour large swaths of forest and foliage. When trees are repeatedly defoliated, they are rendered more susceptible to other pests and diseases, potentially leading to tree death and an increased potential for fire and erosion. In addition, the hairs on caterpillars are known to cause skin irritations and allergies for some people.

Female Spongy Moths & Egg Masses

Young caterpillars feed primarily on oaks, aspen, birch, willows and alder, and older caterpillars feed on a broader range of trees including cedar, pine, spruce and fir. Common California species such as manzanita, western hemlock, Douglas fir and live oak are also prone to damage by this pest.

Spongy Moth Trapping photo

The primary detection method for this invasive pest is through the use of pheromone traps which strongly attract the male moths, trapping them in a glue material. The detection of moths in traps results in the placement of additional traps and/or egg mass survey around the find locations. Based on the results of these additional survey efforts, eradicative measures may be undertaken if the evidence indicates that a breeding population is present. Moth finds are generally the result of persons transporting infested articles when moving to California from infested areas in the northeastern United States or from other countries in Europe and Asia. Outdoor articles such as trailers, boats, lawn items, dog houses, etc. become infested when female moths lay egg masses or caterpillars construct cocoons on them. The strain of spongy moth established in the U.S. is commonly called the European spongy moth (ESM). This is to distinguish it from a strain that exists in Asia, called the Asian spongy moth (ASM). The main difference between the two strains is that females of the ESM can not fly, so its dispersal ability is limited to larval movement, whereas ASM females can fly several miles. In addition, the ASM tends to prefer conifers such as pine and spruce as larval hosts more so than ESM. The ASM has been found entering the U.S. on shipping containers and ships, but has not become established due to early detection and effective eradicative efforts.

CDFA, USDA, and County Agricultural Commissioners have educational posters and pamphlets on SM.

2019 SM Project Decisions
  • Boonville (Mendocino County) - No treatment
    • No SM life stages detected since 2016
    • Reverts to standard detection levels, 2 traps per square mile, as project has ended
  • Compton (Los Angeles County) - No treatment
    • No SM life stages detected since 2016
    • Reverts to standard detection levels, 2 traps per square mile, as project has ended
  • Santa Barbara (Santa Barbara County) - No treatment
    • No SM life stages detected since 2016
    • Reverts to standard detection levels, 2 traps per square mile, as project has ended
  • Soquel (Santa Cruz County) - No treatment
    • No SM life stages detected since 2017
    • Reverts to standard detection levels, 2 traps per square mile, as project has ended
  • Santa Cruz (Santa Cruz County) - No treatment
    • One ASM adult detected in 2018
    • Delimitation trapping beginning May 1, 2019 surrounding find site
  • Orange (Orange County)
    • One ESM adult detected in 2018
    • Delimitation trapping beginning May 1, 2019 surrounding find site
2018 SM Detections
  • On July 24, 2018, one ESM adult was trapped in the city of Orange in Orange County.
  • On July 26, 2018, one ASM adult was trapped in the city of Santa Cruz in Santa Cruz County. This detection is approximately 1/3 mile in a northwesterly direction from the 2017 ASM detection in Santa Cruz.
  • Statewide Detection Trapping : The trap density for statewide SM detection is two traps per square mile. In addition, 25 traps per square mile are placed for ASM detection around high risk seaports. In coordination with the County Agricultural Commissioners, the California Department of Food and Agriculture deploys and monitors SM traps throughout the State. There are approximately 18,000 traps placed and monitored statewide during SM flight season.
  • Delimitation Trapping : When an ESM is detected, additional traps are deployed within a 4-square mile area to determine the extent of the infestation. When an ASM is detected, additional traps are deployed within a 100-square mile area. Traps are monitored for two flight seasons after the last moth is detected.
2017 SM Detections
  • 1 adult ESM in Soquel (Santa Cruz County)
  • 1 adult ASM in Santa Cruz (Santa Cruz County)

How We Can Stop Spongy Moth

Final 2017 Spongy Moth SAP Recommendations


Contact the CDFA Toll-Free Pest Hotline (1-800-491-1899 ) to report suspicious insects or disease symptoms on your property. Help to protect California from invading pests and diseases.