Scrub Hub: The spongy moth is 'devastating' forests across U.S. and it's coming to Indiana

I don’t know about you, but something with spongy in the name doesn’t really imply danger. Maybe soft and squishy, but certainly not “the most serious forest defoliator in the United States.”

Despite the name, the spongy moth has natural resources experts across Indiana and the region shaking in their boots.

If the name is not familiar, that’s because the pest recently got a new moniker. Previously called the gypsy moth, the Entomological Society of America changed the name to remove the derogatory term for the Romani people.

Even though the name is new, these moths have been in the U.S. for a long time. Still, they are not native to the country. They are originally from Europe and were accidentally introduced in Massachusetts in 1869. Since then, they have spread steadily westward.

State officials and bug experts are trying to keep them from spreading even further.

The gypsy moth feeds on more than 300 species of trees.
The gypsy moth feeds on more than 300 species of trees.

For this next edition of the Scrub Hub, we are looking at some key questions about the spongy moth: What makes them so harmful? And what can Hoosiers do about them?

To answer these questions, we spoke with an expert from the state’s Department of Natural Resources to learn more about invasive pest and efforts to stop them.

Short answer: Why are spongy moths so harmful?

The spongy moth landed in Steuben County — the northeast corner of the state where Indiana abuts Michigan and Ohio — in 1998. Since then, it has spread to most northern counties and even further south in the northeastern part of the state.

There are currently nine counties in Indiana are under quarantine for spongy moth, meaning the pest is established in that area. There are two other counties, Lake and Whitley, that are being added to that list.

Wherever these bugs are, they are “the most serious forest defoliator in the United States,” according to Purdue University. Indiana’s DNR agrees, calling the spongy moth one of “the most devastating invasive forest pests” in North America.

Just last year, the spongy moth defoliated over nine million acres of forest in the country, Purdue said. Nearly one million of those acres was in Michigan alone, where the moth has a strong presence.

It’s actually the caterpillar stage of the moth that is known for its voracious and harmful appetite.

The spongy moth caterpillar feeds on over 500 different species of trees and shrubs, said Kristy Stultz, a nursery inspector and compliance officer with DNR’s Division of Entomology and Plant Pathology. She said that make it “easy for it to find a good food source.”

Oak leaves are their preferred food, but the caterpillars also likes poplar, birch, apple, spruce and pine trees. While most trees will produce new leaves after defoliation, repeated snacking can cause some serious issues.

Annual defoliation can cause a great deal of stress on deciduous species, which can lead to a tree’s death in two to four years. A single incident can kill evergreen species, Stultz said.

Long answer: How do they spread and how do I get rid of them?

Adult female spongy moths in the U.S. cannot fly, so spread often occurs by other means. Young caterpillars, for example, can crawl to treetops and are blown by the wind.

One of the main ways, however, the moth moves out of what is considered infested areas is through human movement — unknowingly increasing the rate of spread.

The female will lay egg masses on just about any surface that offers some protection, and the eggs can be difficult to find even when looking for them. It’s then very easy for a person moving a camper, outdoor play equipment or even just a car from northern Indiana to an area where the moth does not yet occur.

Egg masses can contain anywhere from 500 to 1,000 eggs, Stultz said, “so it doesn’t take a lot to create a new population in areas where it doesn’t currently occur.”

The last time an Indiana county was added to the state’s quarantine list was in 2011, “so we have been very effective at managing this pest,” Stultz said. The state entomologist uses trapping data and other information to determine if and when an area will be added.

There are different things the state has done to help slow or control the spread of the spongy moth, and the treatment options depend on things like the location and extent of the population.

If it’s a localized defoliation or egg mass, spraying those trees with horticultural oil may be an option. If the population is beyond that and known to be established, Stultz said an aerial application of what’s called Bacillus thuringiensis kurstaki may work best. Commonly referred to as Btk, it’s considered non-toxic to plants and animals other than very specific insects.

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Stultz said another option is what’s known as mating disruption. That’s also achieved through an aerial application, this time of a pheromone that makes it nearly impossible for males and females to find each other to mate.

The state relies heavily on an extensive trapping program to locate and monitor populations and to determine when and where to do management for spongy moth.

In addition to state efforts, there is a lot that Hoosiers can do to help stop the spread.

In large numbers, spongy moth larvae have been known to defoliate huge tracts of forests in the Midwest. The caterpillar feeds on over 500 different species of trees and shrubs, but oak leaves are their favorite. Experts say they are "the most serious forest defoliator" in the country.
In large numbers, spongy moth larvae have been known to defoliate huge tracts of forests in the Midwest. The caterpillar feeds on over 500 different species of trees and shrubs, but oak leaves are their favorite. Experts say they are "the most serious forest defoliator" in the country.

The first step is being able to identify them in their various life stages.

August is the time of year when adult moths are mating and laying their eggs, before they die at the end of the season. Those eggs do not hatch until the following spring between late April and early May.

The caterpillar stage usually lasts for about seven weeks before going into its cocoon. Adults typically emerge in July to continue the cycle.

Given that timeline, “now is a great time to be on the lookout for” spongy moth egg masses, Stultz said. The masses can be found overwinter until caterpillars hatch in the early spring.

Be on the lookout for a mass that is covered with tan or buff-colored hairs. If the eggs are found, they can be scraped off into a bucket of soapy water and left to soak for a couple of days before being discarded, according to Stultz.

Spongy moth egg masses on a tree trunk.
Spongy moth egg masses on a tree trunk.

A key thing for Hoosiers is to be aware of these pests and know where the populations are so appropriate precautions can be taken. Stultz encourages people to check their equipment, campers and cars if they are traveling to ensure they aren’t giving a ride to moth eggs that might be hitch-hiking.

And “if you are anywhere in the state, and you have defoliation caused by spongy moth caterpillars, DNR wants to know,” Stultz said. This is especially true if Hoosiers are outside of a quarantined county and believe that they have spongy moth.

All reports can go to or can be made by calling 1-866-NO-EXOTIC. People reporting should make sure to provide their name, contact information, location and what they are reporting — all this helps ensure reports get to the nearest DNR inspector so they can be handled in a timely manner.

If you have more questions about spongy moth, other pesky harmful pests that are causing problems in Indiana, or any other topics, let us know!

You can ask us by submitting a question through our Google form below. Can’t see the form? Click here.

Call IndyStar reporter Sarah Bowman at 317-444-6129 or email at Follow her on Twitter and Facebook: @IndyStarSarah. Connect with IndyStar’s environmental reporters: Join The Scrub on Facebook.

IndyStar's environmental reporting project is made possible through the generous support of the nonprofit Nina Mason Pulliam Charitable Trust.

This article originally appeared on Indianapolis Star: The spongy moth is "devastating" for forests and it's here in Indiana