Insect

Spongy Moth Population In Decline

Posted on by akabelowsky
A photo of a tree trunk showing spongy moth caterpillars killed by nucleopolyhedrosis virus (NPV) hang in an inverted “V” orientation; caterpillars killed by the fungus Entomophaga maimaiga hang vertically.

Spongy moth caterpillars killed by nucleopolyhedrosis virus (NPV) hang in an inverted “V” orientation; caterpillars killed by the fungus Entomophaga maimaiga hang vertically. / Photo Credit: Wisconsin DNR

By Michael Hillstrom, Wisconsin DNR Forest Health Specialist
Michael.Hillstrom@wisconsin.gov; 608-513-7690

Spongy moth caterpillars began hatching at the end of April in 2025 and are now actively feeding on leaves. In most Wisconsin locations, though, the population will not be as high as it has been in the last few years.

Wisconsin has had the largest outbreak in state history over the past few years. Fortunately, the outbreak collapsed in many areas of the state in 2024. The wet spring weather in April and May of 2024 allowed a fungus and a virus that infects spongy moth caterpillars to cause heavy mortality. Although some hot spots still exist in south central and northeast Wisconsin, we expect those populations to decline in 2025.

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More Spruce Budworm Defoliation Expected

Posted on by akabelowsky
A close-up photo showing young spruce budworm larvae beginning to feed as buds break, causing the new growth to crook where feeding damage occurs. Webbing is also common.

Young spruce budworm larvae begin feeding as buds break, causing the new growth to crook where feeding damage occurs. Webbing is also common. / Photo Credit: Linda Williams, Wisconsin DNR

By Linda Williams, Wisconsin DNR Forest Health Specialist
Linda.Williams@wisconsin.gov or 920-360-0665

From early indications, the spruce budworm outbreak in some areas of northern Wisconsin is preparing to continue for yet another year.

During the third week of May, expanding buds on balsam fir trees were already showing damage from the tiny larvae.

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Forest Tent Caterpillar Outlook Stays Low

Posted on by akabelowsky
A close-up photo showing forest tent caterpillar larvae displaying gregarious behavior and feeding on a tree leaf.

Forest tent caterpillar larvae displaying gregarious behavior and feeding on a tree leaf. / Photo Credit: Paul Cigan, Wisconsin DNR

By Paul Cigan, Wisconsin DNR Forest Health Specialist
Paul.Cigan@wisconsin.gov or 715-416-4920

Forest tent caterpillar (FTC) populations do not appear to be making a significant return this growing season.

Spring egg mass surveys indicate that populations continue to remain low, continuing the longest documented interphase between outbreaks on state record, at 22 years and counting. The interphase provides some relief for the health of aspen stands recovering from several consecutive years of recent spongy moth defoliation.

Continue reading “Forest Tent Caterpillar Outlook Stays Low” →

Web-Spinning Caterpillars Not Spongy Moth

Posted on by akabelowsky

By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov,  920-360-0665

You may already be seeing the web nests created by eastern tent caterpillars, which hatch early in the spring and start feeding on emerging leaves as the weather warms up.

Eastern tent caterpillars can sometimes be mistaken for forest tent caterpillars or spongy moths. Check out the DNR’s comparison fact sheet, which includes pictures for identification and control options. Continue reading “Web-Spinning Caterpillars Not Spongy Moth” →

UW-Madison’s Raffa Talks Trees’ Natural Defenses

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Photo of Ken Raffa, professor emeritus with the University of Wisconsin-Madison Department of Entomology.

Ken Raffa, professor emeritus with the University of Wisconsin-Madison Department of Entomology. / Photo Credit: University of Wisconsin-Madison

By Art Kabelowsky, DNR Outreach and Communications, Fitchburg
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167

Do you pity the poor tree, forced to stand defenseless against the ravages of insect pests, fungi and disease?

Then, you have not listened to Dr. Ken Raffa discuss the impressive natural defenses trees have developed.

Raffa, a professor emeritus with the University of Wisconsin-Madison’s Entomology Department, recently appeared on Proforest Podforest podcast to discuss the topic “Inside the Tree’s Natural Defense.”

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La Crosse County Added To Spongy Moth Quarantine

Posted on by akabelowsky
A closeup photo of a spongy moth caterpillar consuming a leaf.

A spongy moth caterpillar consumes a leaf. / Photo Credit: Bill McNee, Wisconsin DNR

By Wisconsin Department of Natural Resources (DNR)

La Crosse County has become the latest Wisconsin location to be added to the state and federal spongy moth quarantine, joining most eastern and central Wisconsin counties already considered to be infested by the invasive insect.

The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) announced the change on April 1, based on trapping data collected last year.

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Treat Ash Trees Against Emerald Ash Borer This Spring

Posted on by akabelowsky
A photo of an ash tree next to a park trail in Winnebago County showing damage from woodpeckers feeding on EAB larvae beneath the bark.

An ash tree next to a park trail in Winnebago County shows damage from woodpeckers feeding on EAB larvae beneath the bark. / Photo Credit: Bill McNee, Wisconsin DNR

By Bill McNee, Forest Health Specialist
Bill.McNee@wisconsin.gov or 920-360-0942

Property owners with healthy, valuable ash trees are encouraged to treat them with insecticide this spring to protect against emerald ash borer (EAB).

The invasive pest is currently the most damaging threat to trees in Wisconsin, killing more than 99% of the ash trees it infests.

Continue reading “Treat Ash Trees Against Emerald Ash Borer This Spring” →

Now Is Time To Seek Out Spongy Moth Egg Masses

Posted on by akabelowsky
Large egg masses are seen on a tree at the Kettle Moraine State Forest-Southern Unit in 2021.

Large egg masses are seen on a tree at the Kettle Moraine State Forest-Southern Unit in 2021. / Photo Credit: Bill McNee, Wisconsin DNR

By Bill McNee, DNR Forest Health Specialist, Oshkosh;
Bill.McNee@wisconsin.gov or 920-360-0942

It might be a bit chilly these days, but spring is coming. When the weather warms up, the annual return of spongy moth caterpillars will begin.

There’s a way for landowners to make a dent in the population of the hungry caterpillars: Get out now to locate and properly dispose of spongy moth egg masses, produced by adult moths last summer.

Continue reading “Now Is Time To Seek Out Spongy Moth Egg Masses” →

Make Plans Now To Fight Spongy Moth In 2025

Posted on by akabelowsky
A photo showing large egg masses on a tree at the Kettle Moraine State Forest-Southern Unit in 2021.

Large egg masses are seen on a tree at the Kettle Moraine State Forest-Southern Unit in 2021. / Photo Credit: Bill McNee, Wisconsin DNR

By Bill McNee, DNR Forest Health Specialist, Oshkosh
Bill.McNee@wisconsin.gov or 920-360-0942

Part Two of a report on spongy moth in Wisconsin in 2024 and 2025. Part One was published in December.

The Wisconsin Department of Natural Resources (DNR) is encouraging property owners to examine their property for spongy moth egg masses and plan for action this spring if needed. Each spongy moth egg mass contains hundreds of eggs that will hatch into hungry, leaf-eating caterpillars this spring. Large numbers of these invasive caterpillars can be a tremendous nuisance that may cause tree mortality.

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Woodpecker Flecking On Ash Means EAB

Posted on by akabelowsky
Photo showing that woodpecker flecking on green ash and white ash, from birds feeding on emerald ash borer larvae, will often be extensive and very noticeable.

Woodpecker flecking on green ash and white ash, from birds feeding on emerald ash borer larvae, will often be extensive and very noticeable. / Photo Credit: Linda Williams, Wisconsin DNR

By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665

Ash trees that are flecked by woodpeckers will have the outer layers of their bark chipped off by the birds. Woodpeckers do this to punch through the remaining bark more easily to get at the tasty emerald ash borer (EAB) larvae living there.

Flecking usually starts at the top of the tree, providing a sure sign that insects are under the bark. Although the problem could be caused by ash bark beetles, the more common culprit is EAB.

Continue reading “Woodpecker Flecking On Ash Means EAB” →