'Spongy moth' a danger to PA forests

May 3—Anyone who has taken part in recent outdoor activities has likely noticed skinny, black caterpillars crawling around. Commonly known as spongy moths, the destructive, invasive pest has made its presence known across Pennsylvania forests.

The spongy moths (Lymantria dispar dispar, formerly known as the gypsy moth) are generally not harmful to humans, but can be irritating nonetheless, according to Ryan Reed, Natural Resource program specialist for the Bureau of Forestry.

Reed said spongy moths do not actively seek humans to bite, but have an irritating protein exuded onto their hairs, which are tiny and prickly.

"You can get a little bit of the protein or toxin on your skin and it can be extremely irritating and produce a rash," Reed said. "The immediate follow-up would be to wash it with soap and water."

A topical lotion could also be applied to calm the rash, according to Reed

The best defense against the caterpillars is to cover your skin. Reed suggested wearing long sleeves, pants, closed-toe shoes and a hat.

Though not particularly dangerous to humans, in Pennsylvania forests, the pests are wreaking havoc.

The Department of Conservation and Natural Resources announced they would begin aerial spraying of state woodlands to combat the spongy moth earlier this week.

"Suppression efforts are underway as the caterpillars emerged and began feeding," Secretary Cindy Adams Dunn said. "Aerial suppression is needed to keep this invasive pest in check and protect our native forests from defoliation, with oaks being one of its favorite hosts. Keeping our forests healthy is of paramount importance, to protect all of the values our forests provide, including recreation, habitat, timber, clean air and clean water."

The department is attempting to minimize defoliation to prevent trees becoming stressed and succumbing to disease, other insects or drought.

The bureau will use insecticides tebufenozide or Bacillus thuringiensis subsp. kurstaki which must be ingested by young caterpillars as they feed on the foliage.

The insecticides have been reviewed by both state and federal agencies and have been deemed safe. They are commonly used in agriculture, according to the department.

In 2023, the pest defoliated 441,819 acres in Pennsylvania, the department said.

The department's Bureau of Forestry will oversee the spraying of 185 sites, a total of 227,820 acres including portions of 12 state forests and 18 state parks in 20 counties across the commonwealth, according to a press release.

Oaks are especially vulnerable to infestations and begin to suffer when 30 percent or more of their leaf surface is lost. Tree mortality occurs when heavy infestation persists for two to three years, the bureau said.

Locally, the Raymond B. Winter State Park and Sand Bridge State Park, both outside Mifflinburg, are on the list to be treated.

In March, Park Manager Michael Crowley announced nearly 700 hazardous trees would be removed from Raymond B. Winter State Park. Many of the trees to be removed were affected by spongy moths and late frosts over the past two years, Crowley said.

Private landowners need to be alert for infestation

Reed explained the bureau can only spray the public lands it manages while 70 percent of the forests in Pennsylvania are owned by private residents.

"The biggest thing the general public should understand is if you want to treat your private forest for spongy moths, you cannot do it effectively when you are noticing the problem. It must be planned for well in advance," Reed said. "There are licensed aerial applicators across the state who carry out these operations, but they usually can't do it spur of the moment."

Those looking into getting a competent spray program, might considering banding together with neighbors so a larger area can be sprayed, Reed suggested. "There is power in numbers," he said.

The insects go through cycles and outbreaks generally occur every five to ten years, according to Forest Health Manager Rosa Yoo.

"We are entering in our 4th year of the outbreak cycle, and egg mass surveys from last year determined the need for suppression efforts again this year," Yoo said. "The good news is that we observed a decline in spongy moth defoliation from 850,000 acres in 2022 to 440,000 acres in 2023, signifying a decline in spongy moth populations and the importance of these suppression activities to help continue to reduce spongy moth populations."

Reed said it's time for people to get serious about suppressing the pests.

"This is something we have been harping on for three years now. People need to mobilize and get serious about controlling measures and start planning for it," he said. "You can have foresters come survey for spongy moths and see if you need a treatment."

The bureau has a plethora of information available on its website at https://www.dcnr.pa.gov/Conservation/ForestsAndTrees/InsectsAndDiseases/SpongyMoth/Pages/default.aspx, according to Reed.

"If people really learn the best way to take care of this pest, our forest would be a lot better for it," he said.