Sunnyvale spotting of Asian gypsy moths has local gardeners worried

INVASIVE PEST Asian gypsy moth caterpillars can be easily mistaken for tent caterpillars or webworms.

Asian gypsy moths have just been spotted in Sunnyvale and officials are worried. You should be, too, because these invasive new pests can fly to the South Valley.

A single Asian gypsy moth caterpillar can eat one square foot of foliage in a single day. Fruit and nut trees are vulnerable, along with oak, elm, sweetgum and more than 500 other plant species. If this defoliation doesn’t kill your tree or shrub, it will be more susceptible to other pests and disease. Adding insult to injury, these caterpillars have hairs that may irritate your skin and may cause allergic reactions that can last two weeks.

Asian gypsy moths were first seen in the U.S. in May, in Snohomish County, Wash. They are now found in Oregon, Georgia, Oklahoma, South Carolina and California. Also known as Hokkaido gypsy moths, these pests are not the same thing as European gypsy moths. European gypsy moths are bad news, too. In 2017, European gypsy moths defoliated one-third of the state of Massachusetts, resulting in the loss of one-fourth of its oak trees the following year.

Invasive pests, like the Asian gypsy moth, have the potential to wipe out entire forest ecosystems, not to mention your garden and landscaping, because many of them have no natural pests and indigenous trees and other plants have not evolved their own protections.

Easily mistaken for tent caterpillars or webworms, Asian gypsy moth caterpillars start out less than 1/8-inch long and tan. As they feed and grow, they may reach three and a half inches in length, with two rows of blue and red spots along their backs. Fully mature caterpillars may have a mottled grey color that can range from yellow to black.

Adult female moths are white and somewhat larger than most of our native moths, with a three-and-a-half-inch wingspan. Males are grayish brown and smaller, with a wingspan of only one and a half inches.

A single female Asian gypsy moth can lay 500 to 1,500 eggs. These fuzzy buff or yellowish egg masses may be seen on tree trunks and branches, as well as fences and patio furniture. Each egg mass averages one and a half inches wide by three-quarters of an inch, though they may be as small as a dime.

Washington state pest agencies are spraying “Bacillus thuringiensis var. kurstaki” (Btk). Btk is a type of soil bacteria that kills the Asian gypsy moth but is not harmful to pets, people, fish or bees. The California Department of Food and Agriculture is currently placing 2,300 traps over 81 square miles of the Sunnyvale area.

If Asian gypsy moths arrive in your garden, it is critical that you report sightings to state officials right away by calling the Pest Hotline at 1-800-491-1899.

Kate Russell is a UCCE Master Gardener in Santa Clara County. For information, visit or call 408.282.3105 between 9:30am-12:30pm, Monday through Friday.

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About Kate Russell
Kate Russell is a UCCE Master Gardener in Santa Clara county.