Gypsy Moth Management
Protecting Norwich Township's trees and woodlands from invasive spongy moth
Note: The common name "gypsy moth" was officially changed to "spongy moth" in 2022 by the Entomological Society of America. Both names refer to the same insect (Lymantria dispar). Township documents may use either name.
The spongy moth (formerly known as the gypsy moth) is one of the most destructive invasive forest pests in North America. In Michigan, repeated defoliation by spongy moth caterpillars can weaken and kill oak, aspen, and other hardwood trees. Norwich Township participates in Newaygo County's aerial spray program and provides resources to help residents monitor and manage infestations on their property.
About the Spongy Moth
Spongy moth caterpillars hatch in late April to early May and feed voraciously on tree leaves through June. A single caterpillar can consume one square foot of foliage per day. Healthy trees can typically survive one or two years of defoliation, but repeated attacks — combined with drought or other stressors — can kill even mature oaks. The moth completes one generation per year. Adult moths emerge in July; females lay tan, spongy egg masses on tree trunks, rocks, and outdoor furniture that hatch the following spring.
Life Cycle
Egg Mass
Tan, spongy masses laid on tree bark, rocks, and structures. Each mass contains 100–1,000 eggs.
Caterpillar
Hairy caterpillars with blue and red dots feed on leaves. Peak feeding in May–June causes visible defoliation.
Pupa
Caterpillars pupate in bark crevices and leaf litter for 10–14 days before emerging as adults.
Adult Moth
White females (flightless) and brown males emerge. Females lay egg masses before dying. Cycle repeats.
Newaygo County Aerial Spray Program
Newaygo County coordinates an opt-in aerial spray program using Btk (Bacillus thuringiensis var. kurstaki), a naturally occurring soil bacterium that is toxic to caterpillars but harmless to humans, pets, birds, and most other insects. Spraying typically occurs in May when caterpillars are small and most vulnerable.
Property owners must opt in each year by the county deadline (typically late winter). The county contracts with a licensed aerial applicator. Spray flights occur during calm, dry weather in May. Treatment is most effective when caterpillars are in their early instars (small).
Opt In to the Spray Program
To participate, contact Newaygo County MSU Extension or the County offices before the annual deadline. Norwich Township does not administer the spray program directly — enrollment is handled at the county level.
About Btk (the spray)
- Btk is approved for organic farming and is safe for humans, pets, and wildlife.
- Effective only against young caterpillars (instars 1–3); less effective on large caterpillars.
- Breaks down quickly in sunlight — no long-term residue in soil or water.
- Does not affect adult moths, eggs, or pupae — timing of application is critical.
What Residents Can Do
Scrape and destroy egg masses
In fall and winter, scrape tan spongy egg masses from tree trunks, firewood, lawn furniture, and vehicles into a container of soapy water. Let soak for 48 hours before discarding. This is the single most effective thing a homeowner can do.
Use burlap bands
Wrap burlap around tree trunks at chest height in late May. Caterpillars shelter under the burlap during the day. Check daily and drop caterpillars into soapy water. Remove bands in fall.
Apply sticky bands
Sticky bands (Tanglefoot or similar) applied around tree trunks can trap caterpillars as they climb. Protect tree bark with a layer of duct tape or fabric before applying sticky material.
Treat with Btk or Spinosad
Homeowners can purchase Btk or Spinosad-based sprays at garden centers for ground-level treatment of individual trees. Apply when caterpillars are small (late April to mid-May). Follow label directions.
Keep trees healthy
Water trees during drought, avoid soil compaction near roots, and do not over-fertilize. Healthy trees are better able to survive defoliation and re-leaf in the same season.
Do not move firewood
Egg masses are easily transported on firewood. Do not move firewood from infested areas. Buy firewood locally and burn it where you buy it.
Natural Controls
Spongy moth populations naturally cycle between outbreak and collapse. Two naturally occurring pathogens — a nucleopolyhedrovirus (NPV) and the fungus Entomophaga maimaiga — can cause dramatic population crashes, especially in wet spring weather. These pathogens are present in Michigan and provide long-term biological control. Population outbreaks typically last 2–4 years before collapsing naturally.
Questions? Contact the Township
For questions about the township's participation in the county spray program or to report a severe infestation, contact the Township Clerk.
Report a severe infestation: If you observe widespread defoliation across multiple acres, contact the Michigan Invasive Species Program or call the Michigan DNR at 800-292-7800.
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