Asian Gypsy Moths

Asian gypsy moths have just been spotted in various locations and officials are worried.

You should be, too, if you live anywhere these pests have been found. A single Asian gypsy moth caterpillar can eat one square foot of foliage in a single day. Every day. For weeks.

Asian gypsy moth caterpillar (John H. Ghent and Manfred Mielke, USDA, bugwood.org) Public Domain

And they love fruit and nut trees, along with oak, elm, sweetgum and more that 500 other plant species. If the leaf loss doesn’t kill your tree or shrub, it certainly becomes more susceptible to other pests and disease. Adding insult to injury, these caterpillars have hairs that can irritate your skin and may cause allergic reactions that can last two weeks.

Spreading invasive pests

A single female Asian gypsy moth can lay 500 to 1,500 eggs and mature moths can fly 20 to 25 miles from where they started. This means they can spread rapidly. They also hitch rides on shipping containers, RVs, firewood, patio furniture, and your shoes.

These pests were first seen in the U.S. earlier this year (May 2020), in Snohomish County, Washington. One month later, these moths were found in Oregon, Georgia, Oklahoma, and South Carolina. Now they are in California. Did I mention that these pests travel quickly?

Asian gypsy moths have the potential to wipe out entire forest ecosystems, not to mention your garden and landscaping. Once pests like these become established in an area, widespread quarantines of produce, flowers, plants, and lumber are often necessary.

Different types of gypsy moths

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 have the potential to cause devastating damage because many of them have no natural pests and indigenous trees and other plants have not evolved their own protections.

There are several subspecies of Asian gypsy moth which all look very similar: Lymantria dispar asiatica, L. d. japonica, L. albescens, L. umbrosa, and L. post-alba. You don’t need to learn how to tell them apart (unless you’re into that sort of thing). What is important is learning how to recognize them and reporting them right away.

Male and female adult Asian gypsy moths (USDA Fact Sheet) Public Domain

Asian gypsy moth description

Easily mistaken for tent caterpillars or webworms, Asian gypsy moth caterpillars start out less than 1/8” long and tan. As they feed and grow, they may reach 3-1/2” in length, with two rows of blue and red spots along their backs. Fully mature caterpillars may have a mottled gray color that can range from yellow to black.

Adult female moths are white and somewhat larger than most of our native moths, with a 3-1/2” wingspan. Males are grayish brown and smaller, with a wingspan of only 1-1/2”.

Cluster of Asian gypsy moth eggs and adults on tree trunk (John H. Ghent and Manfred Mielke, USDA Forest Service, bugwood.org) Public Domain

Fuzzy buff or yellowish egg masses may be seen on tree trunks and branches, as well as fences, walls, and patio furniture. Each egg mass averages 1-1/2” wide by 3/4”, though they may be as small as a dime.

Asian gypsy moth control

The first step in controlling these pests is prevention. Always inspect imported products carefully for signs of pests and place new plants in quarantine.

Once they appear, it takes a concerted effort to control them. Washington state pest agencies are spraying Bacillus thuringiensis var. kurstaki or Btk. Btk is a soil bacteria that kills the Asian gypsy moth but is not harmful to pets, people, fish, or bees.

Before you can spray Asian gypsy moths, you have to know where they are. The California Department of Food and Agriculture and the United States Department of Agriculture are currently placing 2,300 traps over 81 square miles of the Sunnyvale area. If you see one of these traps, please leave them alone. If an agency asks permission to place a trap on your property, please say yes.

If Asian gypsy moths arrive in your garden, it is critical that you report sightings to State or Federal officials right away. If you live in California, you can use the Pest Hotline at 1-800-491-1899. Otherwise, contact your local County Extension Office.

By reporting sightings to officials right away, they are coordinate their efforts more effectively.