Spongy Moth – Gypsy Moth – Lymantria dispar
Spongy Moth – Gypsy Moth – Lymantria dispar
Description of Insect:
The Spongy Moth (Lymantria dispar), formerly known as the Gypsy Moth, is one of the most destructive invasive forest pests in North America. Native to Europe, this species has become a major threat to forests in the United States and Canada. It is known for its ability to defoliate vast areas of woodland, leading to tree stress, mortality, and long-term ecological changes.
Adult male Spongy Moths are light brown and capable of flight, while females are larger, cream-colored, and flightless. The most destructive stage of this insect’s life cycle is the larval stage. The hairy caterpillars are easily recognizable, featuring five pairs of blue spots followed by six pairs of red spots along their back.
These larvae can consume massive amounts of foliage, stripping trees bare and leaving them vulnerable to disease and secondary pests. Their adaptability to a wide range of host trees and ability to spread quickly through egg masses make them one of the most challenging invasive species to control.
Life cycle of Spongy Moth:
The lifecycle of the Spongy Moth consists of four distinct stages: egg, larva (caterpillar), pupa, and adult. The cycle begins when females lay tan-colored, fuzzy egg masses on tree bark, outdoor furniture, or even vehicles in late summer. Each egg mass can contain 50-800 eggs, allowing for rapid population growth.
In spring, caterpillars hatch and begin feeding on leaves. They grow through five to six instars, shedding their exoskeleton as they increase in size. The caterpillars are also known for their ability to travel long distances by “ballooning,” using silk threads. They are passively carried by the wind to new locations, allowing wider spread.
By June or July, fully grown caterpillars enter the pupal stage, forming dark brown cocoons in protected areas. After about 10-14 days, adult moths emerge. Males actively seek out females using pheromones, and after mating, females lay egg masses to complete the cycle. The moths do not feed as adults and die shortly after reproduction. The species usually undergoes one generation per year.
Damage they cause:
Spongy Moths are among the most damaging defoliators of hardwood forests, affecting both natural ecosystems and urban landscapes.
- Ecological Impact:The caterpillars feed on over 300 species of trees and shrubs, with a preference for oaks, maples, and birches. A single caterpillar can consume up to a square foot of leaves per day, and during outbreaks, millions of acres of forest can be defoliated. While many healthy trees can survive one or two years of defoliation, repeated infestations can kill weakened trees. It also impacts the native forest-dwelling bird species by reducing their potential nesting sites, resulting in increased predation.
- Economic Damage:Spongy Moth outbreaks inflict severe financial losses on the forestry industry by reducing timber yields and driving up management expenses. The costs of tree removal, replacement, and pest control add up quickly. In the eastern U.S., this invasive pest causes an estimated $200 million in annual damage, straining both industries and local economies.
- Disruptions to Outdoor Activities:The spongy moth caterpillar causes skin rashes, itching, and respiratory issues due to its irritating larval hairs. Additionally, its widespread defoliation diminishes the aesthetic appeal of parks and gardens, leaving trees bare and landscapes uninviting. This impacts outdoor recreation, tourism, and property values in affected areas.