Gypsy Moth Program



The gypsy moth has been a pest of hardwoods in the Northeastern United States since its introduction in 1869; it was introduced in Massachusetts in an attempt to use it for silk production. That same year, it escaped captivity and naturalized in nearby woodlands. By 1889 it was recognized as a serious forest pest. Established populations exist in all or parts of 19 states from Maine to Wisconsin and south to Illinois and generally in a southeasterly line from Illinois to northeastern North Carolina. By 1932 it reached Pennsylvania in some northeastern counties. Since 1969 every county in Pennsylvania has become infested.
































Fully developed caterpillars are 1 ½ to 2 ½ inches long and hairy. They are generally gray marked with three longitudinal light stripes and a double row of colored spots along the back. The first five pairs of spots are dark blue, and the last six pairs are brick red. The head is yellowish tan with black markings. All of these characteristics, except for the hairiness, are more difficult to discern on younger caterpillars.


The male moth is tan to dark brown with black wing markings. It is a strong, daytime flier. The female moth is off-white with wavy, black bands on the forewings and a row of black dots on the outer margins of all four wings. They are so weighted down with eggs, they are unable to take flight.


Life Cycle:

Caterpillars begin to emerge from the egg masses between late April and early May, depending on local climate conditions. Complete hatch at any one locale will normally occur within one to three weeks. A gypsy moth male will molt five times (six times for females) during the six to eight week period it spends as a larva. When a caterpillar is fully developed, it seeks a protected niche and pupates. After 10-14 days the pupa transforms into an adult. Males usually emerge first and are already flitting about when the females appear. This, combined with a powerful sex attractant the female emits, practically ensures mating. Next, the female lays her eggs (150-1,000) in a mass and covers them with the buff-colored hairs on her abdomen. The adults live only long enough to complete their reproductive function. By the end of summer, a young embryo is developing inside of each egg. There is one generation per year.


Host Species:

Oaks are the preferred host species for feeding caterpillars, but apple, sweetgum, basswood, gray and white birch, poplar, willow and many others serve as hosts. Gypsy moths avoid ash, yellow-poplar, sycamore, black walnut, catalpa, locust, American holly, and shrubs such as mountain laurel, rhododendron and arborvitae. Older larvae will also feed on a number of conifers such as hemlock, pines, spruces and southern white cedar. They feed on the leaves of these trees, interrupting the trees ability to get sunlight and continue its life cycle. A tree can withstand a small attack from the larvae; however, if too much of the canopy is lost the tree will die.



Because the ecological range for this pest is extensive, there are still many states that can expect infestations in the future. Without intervention, this pest spreads about 13 miles a year. The gypsy moth can spread by a variety of means. Newly hatched larvae hang from silken thread they have spun and attached to twigs in the crown of trees. They are quite buoyant in this condition and can be carried great distances by the wind. Mature larvae often migrate several hundred feet to a new location, particularly when food is scarce. Pupae and egg masses are sometimes unwittingly transported interstate when they happen to be attached to forest products, nursery stock, campers, vehicles and outdoor household articles such as deck and lawn furniture. Federal and state regulations require that items to be moved from infested areas must be carefully inspected and certified to be free of gypsy moth life stages.


Biological Control:

There are a dozen or more parasites that attack different life stages of gypsy moth. Birds, small mammals, and some beetles actively search out gypsy moth larvae and pupae. The combined effect of these natural enemies is often sufficient to prevent outbreak. There is also a fungus (Entomophaga maimaiga) and a virus (NPV) that can cause a collapse of the larvae population.


Management procedures:

Gypsy moth is best managed under a system known as Integrated Forest Pest Management (IFPM). An IFPM system is based on sound ecological principles and utilizes all suitable techniques to reduce and maintain pest populations at levels below those that cause significant injury. Information is available for homeowners on gypsy moth management techniques and the cooperative state-federal-county gypsy moth suppression program through your local gypsy moth coordinator.


Contact Information: please call the district (724) 378-1701


Beaver County Conservation District

156 Cowpath Road

Aliquippa, PA 15001

Office: 724.378.1701 | Fax: 724.857.1044