It’s Spongy (formerly Gypsy) Moth Season: What to Expect


Hundreds of newly hatched spongy moth caterpillars swarm around an egg mass. Photo courtesy of Bill McNee, Wisconsin DNR,

By Doug Marrin, STN Reporter

It’s spongy (formerly Gypsy) moth season.

First, let’s talk about that name. In July 2021, the people that name bugs, the Entomological Society of America, announced it was dropping the common name of the voraciously destructive gypsy moth because it is a slur against the Romani people, or Roma, people of Europe. “Gypsy" is considered a pejorative term.

The new name, “spongy moth,” refers to the insect’s light brown, fuzzy egg masses that resemble sponges. Hey, it’s better than “frowny cyclops,” which was one of the suggestions the group had to consider.

Egg masses that are light in color, falling apart, or filled with tiny holes are old and will not hatch caterpillars this year. Photo courtesy of Milan Zubrick, Forest Research Institute Slovakia,

While the name is new, the invasive moth is well known throughout Michigan. In its caterpillar life stage, the insect is a voracious leaf eater.

The Michigan Department of Natural Resources (MDNR) reports spongy moth populations were high last year across Lower Michigan. The worry for many people is if they will face the same plague in 2022.

According to aerial survey data, much of northern Lower Michigan has experienced two or three years of defoliation, typically marking the end of an outbreak cycle. Last fall, a survey of the insects egg masses confirmed the feeding cycle had collapsed. There are a few exceptions in areas of Jackson Co and southwest Michigan.

Egg masses smaller than a quarter are an indication that the NPV virus is causing a decline in spongy moth populations. Photo courtesy of Bill McNee, Wisconsin DNR,

Michigan’s last spongy moth outbreak occurred from 1992 to 1996. Since then, localized outbreaks have happened, but suppression efforts have kept them in check. Spongy moth outbreaks are cyclical and peak approximately every seven to 10 years.

MDNR states, “Outbreaks will continue to occur occasionally in local areas and, yes, every now and then we will have extensive outbreaks like the current one. While an outbreak is not pleasant for people in an affected area, it is rarely a problem for healthy trees and forests.”

If spongy moths, unfortunately, return to your yard this year, you’ve got control options. But keep in mind that you will not be able to eliminate all the caterpillars. Your goal is to reduce the density of population around your house.

Banding is an effective preventative measure against the caterpillars. Photo courtesy of MDNR.

Scraping: If healthy egg masses are found on trees, buildings, or outdoor furniture around the home, act now. Egg masses can start hatching anytime. Use a scraper or hard, plastic card to scrape egg masses into a container of soapy water. Let them soak overnight, then bag and dispose of them. Alternately, egg masses can be placed in a fire and burned.

Banding: Cut a burlap band 18 inches wide and long enough to go around the tree trunk and overlap a bit. Tie a string around the center of the band to make a two-layered skirt around the trunk. When caterpillars climb trees daily to feed, they will get caught in the band. Scrape them into a bucket of soapy water to kill them.

Spraying: To address an infestation in a handful of individual trees, homeowners can purchase a spray containing Bacillus thuringiensis var. kurstaki, a bacterium that naturally occurs in the soil but can be lethal to certain caterpillars and moths. The best time to spray is when caterpillars are small, usually mid-May through early June. Choose an Environmental Protection Agency-registered pesticide and apply it according to the label directions. Remember, there is no good reason to spray woodlots or forested areas. Healthy trees and forests can withstand periodic infestations.

More help can be found at MSU Extension at


MDNR “It’s spongy moth (formerly gypsy moth) season: What to expect in 2022.”
“Insect Experts Will Change The Name Of The 'Gypsy Moth' And 'Gypsy Ant'”
“Invasive Insect Gets a New Name: Spongy Moth”

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