European Gypsy Moth
European gypsy moth (Lymantria dispar L. (Lepidoptera: Lymantriidae)) was introduced to the US from Europe in 1868 in an effort to breed a better silk worm. Soon thereafter, some of the gypsy moths escaped from the lab as a result of a series of accidents. Since no one yet realized the destructiveness of this pest, no efforts were made to kill the escaped moths. They have been spreading outward from Medford, MA, since then. European gypsy moth (EGM) is now known through the entire northeastern US, south into North Carolina and west into Wisconsin with occasional outbreaks in other states. Arkansas has had occasional confirmed reports of EGM, most recently in the summer of 2012.
European gypsy moth damages hardwood trees, mainly oaks and aspens, by skeletonizing the leaves (Fig. 1) thus defoliating the trees (Fig. 2). Tree and shrub species preferred by EGM in our area include oaks, willows, apple, basswood, hawthorns, and witch hazel.
They will also defoliate beech, chestnuts, elms, hickories, walnut, maples, cherries, cottonwood, and ironwood. Healthy trees can tolerate one or maybe two episodes of defoliation; however repeated defoliation will weaken a tree and make it more susceptible to secondary pests that can kill the tree. Even though, EGM primarily attacks hardwood trees, some conifers can be defoliated, as well.
Only the brown male EGM’s (Fig. 3) are capable of flight. The white females (Fig. 4) are not. One would expect this to limit spread of the EGM, but the moth has been spreading rapidly in spite of this limitation. EGM’s breed during late summer. The females lay eggs in sheltered areas under tree bark and on or in many man-made objects including houses, vehicles, grills, toys, and lawn furniture. Eggs overwinter and hatch in the spring. Young caterpillars (Fig. 5) crawl to the top of the tree and disperse by spinning a silk thread that is caught and carried by wind currents, taking the caterpillar with it. The caterpillars graze on leaves for about 7 weeks and then pupate. Adult moths hatch after about 2 weeks of pupation.
The following resources provide some general information about EGM.
European gypsy moth is not hard to distinguish from native moths. Caterpillars are distinct in appearance from our native caterpillars. EGM eggs hatch in early spring, releasing caterpillars that are about 0.1 inch (3 mm) long (Fig. 5). Caterpillars reach a maximum length of about 1.5 to 2 inches (38 to 51 mm) after about 40 days of growth. Look for a double row of spots down the caterpillar’s back (Fig. 6). Starting at the head, the first five pairs of spots will be blue, and the subsequent six pairs of spots will be red. The colors are not always distinct. During early summer the caterpillars enter the pupal stage. Pupal cases range in color from brownish red to very dark brown. The outside of the case has tufts of hairs in rows and reveals outlines of the features of the moths head and wings (Fig. 7). Cases are typically found in clusters in bark crevices, at the base of branches, and at forks in the trunk (Fig. 8). Adults EGMs emerge from the cases two to two and a half weeks later.
Male and female adult EGMs are dissimilar. Males are ¾ to 1 inch (20 – 25 mm) long and light mottled brown with black wing markings (Fig. 3). In contrast, the female EGMs are 1.2 to 1.4 inches (30-35 mm) long and white with brown and black wing markings (Fig. 4). Antennae are also different between the sexes. Males have distinct feathery antennae (Fig. 9) in contrast to the females more thread-like antennae (Fig. 10).
The following resources explain how to identify the European gypsy moth and distinguish it from similar native species.
European gypsy moths breed in midsummer. After breeding, the females lay eggs in clusters on many objects including trees, shrubs, automobiles, trailers, tractors, buildings, lawn furniture, toys, camping equipment, and more. The egg masses are vaguely fan shaped and fuzzy (Fig. 11). Each egg mass contains all of the eggs from one moth, usually from 500 to 1,000 eggs. The eggs are laid in late summer and persist through the winter, hatching in the spring.
Stop the Spread
European gypsy moth does not spread rapidly without help. The following resources explain how to avoid moving EGM moth to new areas. EGM spreads most rapidly when aided by humans. This typically is done accidently when people move objects from a region containing EGM to a region where the pest does not occur. Any object left outdoors can be a vector for spreading EGM.
European gypsy moth infestations can be controlled. The following resources explain how to reduce or control EGM infestations. Attempts to control EGM using pathogens, parasites, and predators have been made through the years. Control using these natural methods can be effective locally but have failed to eliminate EGM from North America.
The most effective strategy to date for limiting the spread of EGM has been homeowner vigilance. If you live in an area where EGM is a problem, thoroughly examine your vehicles before driving them out of the area. If you find EGM egg masses on your vehicles or trailers, scrape the egg masses off and destroy them before leaving the area. Before transporting objects out of an area known to be infested with EGM, thoroughly examine the object for EGM egg masses. Make sure you examine the interiors of objects; inside the tubes of lawn furniture frames, for example. The following documents provide information about preventing the transport of EGM.