**Gypsy Moths** (*Lymantria dispar*) are notorious, invasive forest pests native to Europe and Asia that were accidentally introduced to North America in the late 1860s. The larval stage (caterpillar) is known for its ability to cause massive, rapid **defoliation** of hundreds of species of hardwood trees, particularly oaks. While healthy trees usually survive a single defoliation, repeated annual stripping can lead to tree death, widespread forest damage, and significant economic impact on timber and tourism industries.
Taxonomy and Classification
Gypsy Moths belong to the family Erebidae (tussock moths) in the order Lepidoptera. They undergo complete metamorphosis. The scientific name, *Lymantria dispar*, means “destroyer” and “to separate,” referring to the dimorphism (different appearance) of the male and female adults.
Physical Description
The Gypsy Moth is most easily identified in its larval and egg stages:
- **Caterpillar (Larva):** Grows up to $2.5$ inches long. It is hairy, dark-colored, and most distinctly features **five pairs of blue spots** followed by **six pairs of red spots** running down its back.
- **Female Moth:** Large, off-white to cream-colored, with wavy dark markings. **Cannot fly**; she remains near her egg mass.
- **Male Moth:** Smaller, brownish-gray, and a strong, erratic flyer.
- **Egg Mass:** The most visible stage. A velvety, buff-colored or tan mass, about $1$ to $2$ inches long, laid on tree trunks, rocks, or outdoor furniture, containing hundreds of eggs.
Distribution and Habitat
The Gypsy Moth is widely established across the Northeastern United States and Eastern Canada. Its habitat is forests, woodlots, and urban environments containing host trees (especially oak, apple, birch, and willow). The pest spreads primarily when humans unknowingly transport the protected egg masses on firewood, vehicles, or outdoor equipment.
Behavior and Damage
The moth has one generation per year. It overwinters in the egg stage. Larvae hatch in early spring, climb the trees, and immediately begin feeding on new foliage.
- **Defoliation:** Caterpillars consume vast amounts of leaves before pupating in early summer. Outbreak years result in acres of bare trees in the middle of summer.
- **Stress and Mortality:** Single defoliation rarely kills a healthy tree, but two or more successive defoliations, especially when combined with other stresses (drought, disease), can cause significant branch dieback or tree death.
- **Nuisance and Health:** Hairy caterpillars, their frass (pellets of excrement), and the sheer volume of defoliated leaves are a significant urban and suburban nuisance. The hairs can also cause skin irritation in some people.
Management and Prevention
Control is highly regulated, focusing on slowing the spread and reducing populations during outbreaks.
- **Egg Mass Removal (Winter):** The most effective mechanical method. Scrape the egg masses off surfaces into a container of soapy water and destroy them. **Do not** simply scrape them onto the ground.
- **Banding (Spring):** Apply sticky barrier bands or burlap wraps around the trunks of valuable trees to trap crawling caterpillars.
- **Biological Control:** Spraying foliage with **_Bacillus thuringiensis_ var. *kurstaki* (BtK)**, a naturally occurring bacterium, is the primary control method. It must be applied early when the caterpillars are small and actively feeding.
- **Monitoring:** Pheromone traps are used to monitor the male population and detect new infestations.
Conservation and Research
The Gypsy Moth is managed as a high-priority invasive pest. Research focuses on developing genetically modified biocontrol agents (parasitic wasps and flies) and maximizing the spread of natural pathogens (the *nucleopolyhedrovirus* or “wilt disease”) that cause natural population collapse during outbreaks.