European Gypsy Moth
The European gypsy moth (Lymantria dispar dispar or EGM) is a relatively large moth and easy to identify from native moths. The sexes are distinct in both appearance and behavior. Male moths are brownish and can be seen flying during the day. Male EGM have a wingspan of about 1 ½". Female EGM do not fly and are a bit larger and creamy white in color. Both sexes have a characteristic mark on the forewings that consists of a blackish arc and an accompanying dot near the apex of this arc. This arc-dot combination is diagnostic of Lymantria and easily separates them from native moths. Females lay eggs on tree trunks, outdoor furniture, and other outdoor items then cover them with buff to cream-colored hairs. Egg masses will be visible through winter.
Newly hatched larvae are black with long hairs. Older larvae are distinguishable from all native caterpillars by the presence of five pairs of blue raised “bumps” or spots followed by six pairs of raised brick-red spots along their backs. They are very hairy.
The European gypsy moth (EGM) was introduced to Massachusetts in the late 1860s and since then it continues to expand its range to the west and south. EGM caterpillars feed on over 300 species of trees and shrubs, and when populations are large enough can defoliate the hosts on which they feed. Defoliation weakens trees and can cause tree death when it occurs in consecutive years or in conjunction with other stressors like pest, disease or drought.
Countless measures have been taken over the years to control this voracious pest. In the eastern United States, EGM defoliates an average of 700,000 acres each year, causing millions of dollars in damage. Due to the wide range of hosts and the potential for human-assisted spread, EGM represents a serious threat to our hardwood forests.
EGM is well established in the Northeast and extends its range by its own dispersive means each year. The flightless females limit the spread to some degree, but larvae and males can disperse reasonably well. Additionally, EGM are notorious for hitchhiking! Egg masses on logs or any transportable surface, such as motor vehicles or outdoor equipment transported during a move, can act as a pathway to artificially spread this pest to new locations. If you are moving or traveling, be sure you are not bringing a gypsy moth egg mass with you. Learn more about human-assisted spread of gypsy moth at Your Move Gypsy Moth Free.
If you live in the northeast, there is not much that can be done to prevent EGM's continued occurrence in your region, but you can avoid spreading it south and west while moving or traveling from a state within the quarantine to a state outside of the quarantine.
Do you live in a state battling EGM or one which doesn’t have record of it yet? To see where it has been reported, visit EDDMapS Gypsy Moth map.
A major reason for the severity and success of EGM as a pest is its ability to thrive on many host species. Over 300 species of hosts are susceptible to EGM, though oaks (Quercus spp.), willows (Salix spp.), and birches (Betula spp.), among other common hardwood forest trees are preferred.
The most obvious symptom of EGM is the defoliation of hardwood trees. Young caterpillars chew holes in leaves, especially oaks, in the early summer. As caterpillars grow larger they may chew the leaves from the outer edge inward to the midrib. Additionally, each life stage can be recognized separately.
- Eggs: hairy, buff-colored egg masses on tree trunks, building sidings, rock walls, etc. throughout the late summer, autumn, winter and spring.
- Larvae: hairy caterpillars with blue then red raised spots from head to tail can be found singly on various trees and shrubs or abundantly where defoliation may be occurring.
- Adults: (may be hard to find) large, whitish, flightless female moths are often seen clinging to trees and other vertical surfaces in the late summer. Males are active during the day which is atypical for moths and can be distinguished from brown butterflies by their feathery antennae.
If you want to receive an email notification when larvae will be present in your area, sign up to receive phenology alerts at NPN's Gypsy Moth forecast.
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