**Spongy Moths** (*Lymantria dispar*—previously known as Gypsy Moths) are a notorious invasive species introduced to North America in the 1860s. The larvae (caterpillars) are major defoliators of hundreds of species of deciduous and evergreen trees, particularly **oak, birch, apple, and pines**. The conflict is catastrophic forest destruction: during outbreaks, the larvae consume entire forests, leading to **severe tree stress, growth loss, and the death of millions of trees**, as well as causing an intense nuisance with massive numbers of crawling insects and falling frass.
Taxonomy and Classification
Spongy Moths belong to the order Lepidoptera (Moths and Butterflies). They undergo complete metamorphosis. The caterpillars hatch in the spring and feed for 6-8 weeks. They are famously identified by the large, fuzzy egg mass (resembling a piece of sponge) laid by the female on tree trunks or outdoor objects.
Physical Description
The destructive larvae are 2 to 2.5 inches long.
- **Larva (Key ID):** Hairy, brownish-gray caterpillar with a distinctive row of **five pairs of blue spots** followed by **six pairs of red spots** running along the back.
- **Adult Moth:** Females are large, white, and heavy-bodied with non-functional wings; males are smaller, brown, and good fliers.
- **Damage Sign (Key ID):**
- **Defoliation:** Entire tree canopies stripped of leaves in late spring/early summer.
- **Frass:** High volume of fecal pellets raining down from the canopy.
- **Egg Mass:** Tan, fuzzy, sponge-like egg masses (up to 2 inches long) found on trunks, stones, patio furniture, and walls.
- **Conflict:** Catastrophic forest defoliation and intense personal nuisance.
Distribution and Habitat
Spongy Moths are widespread across the Northeast, Midwest, and increasingly the South of North America. Their habitat is the foliage and bark of host trees in forests, suburban areas, and parks.
Behavior and Conflict
The conflict is dominated by the massive scale of the infestation.
- **Host Range:** They have one of the widest host ranges of any defoliator, allowing them to thrive in almost any forest type.
- **Oak Mortality:** Repeated defoliation of oak trees (their preferred food) drastically depletes energy reserves, leading to high mortality rates, particularly during drought years.
- **Nuisance:** During outbreaks, the ground, patios, and homes are covered in thousands of crawling caterpillars and frass pellets, making outdoor activity unpleasant or impossible.
Management and Prevention
Control is aggressive, coordinated integrated pest management (IPM) across large regions.
- **Scrape Egg Masses:** In winter/early spring, scrape off all visible egg masses and destroy them (e.g., place them in soapy water or alcohol).
- **Banding:** Place sticky tree bands or burlap skirts around trunks in the spring to trap migrating caterpillars.
- **Bt Application:** Aerial application of *Bacillus thuringiensis* (Bt) to large forested areas is highly effective against young larvae.
- **Virus:** The naturally occurring *Ld*NPV virus is highly effective in collapsing high-density populations.
Conservation and Research
Spongy Moths are managed as major, invasive, high-priority forest and landscape pests. Research focuses on developing better pheromone controls, utilizing fungal and viral pathogens to manage populations, and slowing the moth’s relentless spread into new, uninfested territories.