The Spongy Moth Resource Center is the central location for information and resources related to spongy moth for Wisconsin residents and landowners.

Participating State A​​genc​​ies 
  • Department of Agriculture, Trade and Consumer Protection (DATCP)
  • Department of Natural Resources (DNR)
  • University of Wisconsin-Madison Extension (Extension)

Yard Tree Management

​Homeowners who want to protect one or a few trees from spongy moth should consult with a certified arborist for more information. Some options include spraying insecticides, scraping egg masses off surfaces or trapping them using sticky barriers.

Woodlot Management

​Woodlot owners should consult with a forester prior to beginning management. Some available options include doing a private aerial spray of the property or using active forest management to decrease defoliation impacts by improving tree health.

State & Fed. Quarantines

​The quarantine covers 53​ of Wisconsin's 72 counties primarily in the eastern 2/3 of the state. Under quarantine regulations, wood product and outdoor household items must be inspected or certified before moving them from quarantined to non-quarantined areas.​

Frequen​tly Asked Questions 

View all questions and answers in PDF format.

Spongy moth (Lymantria dispar) is one of the most important forest and shade tree pests in the eastern United States. Approximately every eight to 10 years, spongy moth populations can have an outbreak period during which the population is very high, and trees can be stripped of their leaves (defoliated).

Large numbers of spongy moth caterpillars can completely defoliate (eat the leaves) of a tree in a short period of time. Repeated defoliation can weaken trees, resulting in greater susceptibility to disease and other pests.

Spongy moth caterpillars can also be a nuisance when they congregate on the sides of buildings or produce large quantities of frass (droppings) that fall from trees onto lawns, patios and sidewalks. The hairy caterpillars can cause rashes, welts and other irritation if touched.

Additional resources:

Spongy moth caterpillars feed on tree leaves from April or May through July. / Photo Credit: Wisconsin DNR

While spongy moth is a common pest throughout the eastern United States, including Michigan and the eastern three-quarters of Wisconsin, it has yet to establish in many areas of western Wisconsin (see the current Wisconsin spongy moth quarantine map). Adults, caterpillars, pupae and egg masses can be moved long distances when attached to firewood, potted plants, Christmas trees, outdoor furniture, vehicles, trailers and anything else stored near trees. Accidentally moving one egg mass to a non-quarantined county can give rise to new spongy moth infestations.

Check your vehicles, trailers or outdoor items for spongy moth life stages when you are in an area where spongy moth is present. When obtaining firewood, either buy it where you'll burn it, buy certified treated firewood or gather it on-site (where permitted).

Additional resources:

Spongy moth egg masses attached to firewood. / Photo Credit: Wisconsin DNR

Healthy hardwoods generally can endure one or two years of heavy defoliation (around 60-100% of leaf loss) before tree mortality occurs. Healthy trees will normally put out a replacement set of leaves a few weeks later (see photo), though the new leaves may be smaller and lighter in color.

A heavily defoliated tree must use its energy reserves to grow a replacement set of leaves. This weakens trees and makes them more susceptible to disease, drought stress and other insect attacks, which in combination can kill the trees.

You can help valued trees recover from defoliation by watering them deeply each week if there hasn't been a soaking rain. Keep watering the tree until it has dropped its leaves in the fall. Trees generally need the equivalent of 1 inch of rain per week.

Also, avoid giving trees any nitrogen fertilizer as this will overstimulate the tree to produce more replacement leaves than it can support. That may deplete food reserves so much that the tree won't be able to produce leaves the following spring.

Trees most likely to be heavily defoliated include oak, apple, birch, aspen, willow, tamarack and linden. Other deciduous trees and conifers also can be stripped of leaves or needles. If you remain alert to increasing numbers of caterpillars and egg masses, use management options to reduce damage to your trees and provide adequate water through the growing season, you can greatly reduce the chance of your tree dying.

Additional resources:

A tree after complete spongy moth defoliation (left) and leaf regeneration about a month later. / Photo Credit: Wisconsin DNR

As of April 2023, the spongy moth quarantine covers 53 of Wisconsin’s 72 counties. Under quarantine regulations, wood products and outdoor household items must be inspected or certified pest-free before being transported from quarantined areas to non-quarantined areas. Quarantine regulations apply to both businesses and private citizens.

Quarantined counties have well-established populations of spongy moth, even if they aren’t at levels noticeable to casual observers. Non-quarantined counties may have patchy low-level populations, but the pest is not well-established

Additional resources:​

A map showing Wisconsin’s spongy moth quarantine counties (in red). / Map Credit: Wisconsin DATCP

In areas where spongy moth has been established for several years, natural enemies can help keep spongy moth populations in check. Natural enemies include insect parasitoids that attack eggs and caterpillars, predators such as birds and mice, and insect-specific pathogens.

There are two common pathogens that affect spongy moth caterpillars and usually bring an outbreak to an end: Nucleopolyhedrosis virus (NPV) and Entomophaga maimaiga. NPV is a virus that causes caterpillars to die and hang from trees in an inverted “V” orientation. Entomophaga maimaiga is an introduced fungus that primarily infects caterpillars in years when the April-to-June weather has abundant precipitation. Dry conditions during spring limits the impact of E. maimaiga.

Additional resources:

A spongy moth caterpillar droops after being infected with NPV. / Photo Credit: Wisconsin DNR​

If your property is in a quarantined county, spongy moth is well-established; you don't need to report sightings.

However, it is helpful to report spongy moth in non-quarantined counties (white on the statewide quarantine map​).

If you have found spongy moth in a non-quarantined county, please try to take a clear photo and report it to the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) by email at spongymoth@wisconsin.gov or by calling the spongy moth hotline at 1-800-642-MOTH (6684) and selecting Option 1.

Spongy moth caterpillars work their way up a tree trunk to feed on leaves. / Photo Credit: Wisconsin DNR​


The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) participates in a federal Slow The Spread program to reduce the westward spread of spongy moth by finding and treating isolated populations in western Wisconsin where the pest is​ not yet well-established.

Trapping surveys detect newly emerging spongy moth populations, which are treated before they can contribute to large-scale spongy moth spread. Areas selected for treatment are aerially sprayed with either the bacterial insecticide Btk (Bacillus thuringiensis var. kurstaki) or wax droplets containing pheromone, which prevent male moths from locating female moths.

If your home is in or near a spray site, you will receive an informational postcard in late April or early May.

Visit the DATCP website to find more information about the DATCP Slow the Spread program, along with information about the products used, fact sheets and an interactive web map to see if you are located within a treatment block.

An airplane delivers an aerial application of Bacillus thuringiensis var. kurstaki to fight spongy moth caterpillars. / Photo Credit: Wisconsin DNR

There are four options to get information on DATCP's Slow the Spread aerial spray plans, updated daily during the spray season (May through July):

DNR updates for spraying plans on public land

Two adult female spongy moths lay egg masses on a tree trunk. / Photo Credit: Wisconsin DNR​

When determining treatment options, an important consideration is the size of the treatment area and whether you are interested in treating a few or many trees. If a small number of yard trees are defoliated, water them low and slow with the hose weekly to help them recover. About 1 inch of water per week is the general recommendation.

Options such as egg mass oiling or egg mass removal, sticky barrier bands, burlap bands and some insecticides can be used for high-value yard trees or small woodlots. Systemic insecticide injections are an effective way to protect high-value yard trees. Arborists can be hired for insecticide applications.

Forests and larger woodlots should be sustainably managed to increase tree health and resilience. A healthy, mixed-species forest can usually recover from defoliation with minimal losses. Do not thin for one to two years after outbreaks to prevent adding more stress as impacted trees are recovering. Use the spongy moth silviculture guidelines in consultation with a professional forester to determine the most appropriate forest management options.

Natural enemies will ultimately bring outbreaks under control. If tree mortality is not acceptable, such as in high-use areas at parks, then aerial spraying can be considered. Aerial sprays are the most cost-effective and practical tool for suppressing outbreaks in forests of 20 or more acres. See detailed guidance on arranging for an aerial spray of a larger area, such as a woodlot or residential area.

Please note: The State of Wisconsin does not offer a state-sponsored or cost-share program for citizens to sign up their property to be treated for spongy moth.

Additional Resources

A person uses an implement to scrape spongy moth egg masses into soapy water. / Photo Credit: Wisconsin DNR

Please note:The State of Wisconsin does not offer a state-sponsored or cost-share program for citizens to sign up their property to be treated for spongy moth.

Treating spongy moth over larger areas will require hiring a licensed aerial applicator (e.g., plane, helicopter or drone). Property owner groups (such as a lake association) sometimes organize these treatments in residential areas.

Aerial treatments can be expens​ive (often more than $100 per acre) and will require time to organize in advance of a treatment that is usually done between mid-May and early June. An arborist (for residential areas) or forester (for non-residential areas) can be contacted to determine which management strategies would work best.

Additional Resources

An airplane delivers an aerial spray to fight spongy moth at a State of Wisconsin property. / Photo Credit: Wisconsin DNR