Formerly known as the gypsy moth, the spongy moth (Lymantria dispar dispar) was first detected in Washington in 1974. Since the early 1990s, another variety of spongy moth, the Asian spongy moth (L. dispar asiatica), has been intercepted multiple times by WSDA, often as egg masses attached to cargo on ships originating from Asian ports. Over the past 40 years, trapping and rapid response efforts have been successful in preventing permanent populations of either variety of spongy moth in the PNW. In 2019, a closely related moth species known as the Hokkaido moth (L. umbrosa) was detected in Washington. In response, WSDA initiated an eradication program for the Hokkaido moth in spring of 2020.
Pest description and damage The wings of male spongy moths are tan with a series of dark-brown wavy lines and relatively large, feathery antennae. The wingspan of the male moth is about 1.5 inches long. The female moths are larger, about 2-inch wingspan, but sport wings of a much lighter color—cream to white. The female moths of the spongy moth cannot fly, but the female Asian spongy moth can and readily disperse. The moths are most active in summer. The mature larvae have five pairs of distinctive blue dots followed by red dots along their back and can be found late spring to early summer. The larvae of spongy moths feed on over 500 trees, shrubs, and plants including most hardwood and conifer trees found in the Pacific Northwest. In parts of northeastern US, this species defoliates entire forests. Homeowners should be on the lookout for the spongy moth egg masses from late autumn to early spring as these are, by far, the most inadvertently transported stage of this pest. Each egg mass contains hundreds of round eggs covered with a dense mat of light tan hairs and is sponge-like in appearance. These masses are usually laid on the bark of the host trees, but may be found on automobiles, RVs, firewood, doorframes, windowsills, furniture or just about any sheltered surface.
Pest monitoring Traps that rely on lures which release a sex pheromone to attract and monitor male moths are commercially available. WSDA places up to 25,000 green or orange delta traps on host trees throughout the state each summer.
Management This is a quarantined pest species. If you suspect you have found any stage of this insect, please report the finding to the State Department of Agriculture or local university Extension office. When confirmed as a spongy moth, these state agencies will respond and work to eradicate this pest as soon as possible.
For further information:
Crabo, L., R. Zach & M. Peterson. 2019. Pacific Northwest Moths. http://pnwmoths.biol.wwu.edu