**Satin Moths** (*Leucoma salicis*) are an invasive pest moth of Eurasia that feeds primarily on **poplars** (*Populus* species, including aspen and cottonwood) and **willows** (*Salix* species). The conflict is severe defoliation: the larvae (caterpillars) feed rapidly, and high populations can cause **complete defoliation** of host trees. While healthy, native trees can often survive a single defoliation, repeated attacks severely stress the trees, leading to dieback, making them susceptible to secondary pests, and eventually causing tree death.
Taxonomy and Classification
Satin Moths belong to the order Lepidoptera (Moths and Butterflies). They undergo complete metamorphosis. They are characterized by their overwintering behavior as small, partially-fed larvae hidden in crevices in the bark. They emerge in the spring to complete feeding, followed by a second generation in the summer in some regions.
Physical Description
The destructive larvae are 1.5 to 2 inches long.
- **Adult Moth (Key ID):** Striking, pure **silvery white** moth with a satiny sheen (hence the name). They are often seen resting on the host tree during the day.
- **Larva (Key ID):** Dark, brownish-black caterpillar with prominent **white-to-yellow spots** and dense tufts of long, white or yellow-brown hairs. The hairs can cause skin irritation in some people.
- **Damage Sign (Key ID):**
- **Defoliation:** Entire trees stripped of leaves, often by mid-summer.
- **Aesthetic:** The white moths and the conspicuous cocoons can be a nuisance.
- **Conflict:** Tree stress, defoliation, and aesthetic loss.
Distribution and Habitat
Satin Moths are established in the Pacific Northwest and parts of the Northeastern U.S. and Canada. Their habitat is the foliage and bark of poplar and willow trees in forests, shelterbelts, and urban landscapes.
Behavior and Conflict
The conflict is widespread forest and windbreak damage.
- **Aggressive Feeding:** The larvae are aggressive feeders that can rapidly strip an entire tree.
- **Human Irritation:** The hairs on the caterpillars can be **urticating** (cause irritation) when they come into contact with human skin.
- **Stress:** Poplars and willows are often planted as quick-growing windbreaks or ornamental trees; defoliation negates their utility and aesthetic value.
Management and Prevention
Control is integrated pest management (IPM), with a focus on early detection and biological controls.
- **Bt Application:** Apply the biological insecticide *Bacillus thuringiensis* (Bt) as a foliar spray in the spring when the larvae are small and actively feeding.
- For high-value trees, apply a systemic insecticide (e.g., as a soil drench or trunk injection) in the spring to kill the internal feeding larvae.
- Inspect and prune off branches with visible larval webs and destroy them.
Conservation and Research
Satin Moths are managed as invasive, high-priority forest and landscape pests. Research focuses on monitoring their spread, utilizing imported parasitic wasps and flies for biological control programs, and developing rapid detection methods.