Tom Hall lives on a heavily wooded property in Shawneeland, west of Winchester. This spring, he's noticed a lot of spongy moth caterpillars gnawing at the leaves on his oak trees, resulting in a mass of shredded foliage littering his porch deck.
"Some years are worse than others and this year they're particularly bad," the Frederick County resident said recently.
The spongy moth, formerly called "gypsy moth" until a name change by the Entomological Society of America in 2022, is a destructive, non-native insect whose caterpillars defoliate trees and pose a threat to forests and woodlands across North America, according to the U.S. Department of Agriculture.
Local Virginia Cooperative Extension agent Mark Sutphin says the pest's present infestation levels in the Northern Shenandoah Valley are likely the worst in decades.
"The infestation levels that we are seeing in the region are probably the highest they have been in nearly 30 years, going back to when this was a new invasive species to Virginia," Sutphin wrote in an email this week.
"We've seen a resurgence really the last two years," Sutphin noted in a phone conversation. "I think that's been somewhat prompted by the drier springs that we had in 2022 and 2023."
Native to Europe and Asia, the spongy moth — so-called because of its sponge-like egg masses — was brought to the U.S. in 1869 by a researcher in Massachusetts interested in starting a silk industry and breeding a hardy silkworm. It has been a nuisance to U.S. forests ever since. Its range extends as far south as Virginia and as far west as Michigan.
Spongy moth caterpillars, before their transformation into moths, have a voracious appetite and a taste for oak trees, especially white and chestnut oaks situated on ridgetops. Unchecked, the caterpillars will strip foliage from trees and kill them, if severe defoliation persists for multiple seasons, according to the USDA. Adult spongy moths do not eat.
If you've never seen a spongy moth caterpillar, they are black and hairy when newly hatched. As they age, they develop an unmistakable color pattern on their backs showing five pairs of blue dots followed by six pairs of red dots.
According to Sutphin, the region's higher elevation areas are seeing greater levels of spongy moth caterpillar activity. A photo he took this week shows particularly pronounced defoliation on a tree on the west side of Signal Knob near Strasburg in Shenandoah County.
Other photos show spongy moth egg masses as well as caterpillars feeding on an oak tree on a property in western Frederick County, where there has been a sizable hatch of caterpillars this year in the Star Tannery area.
"I would say you can see defoliation on the mountains, both on Signal Knob and down the Massanutten range there and then also to the west in northern Shenandoah County, so I think those areas are actually heavier than what we are seeing in western Frederick County," Sutphin said.
A media release this month from the U.S. Forest Service says the increase in spongy moth numbers over the past two years is fueling forest defoliation in large swaths in the Northern Shenandoah Valley. Additional defoliation will likely cause "significant tree mortality, which would create safety hazards in high visitor-use areas and damage forest habitats," the release states.
In February, a Shenandoah County official told that locality's Board of Supervisors, "We have not seen defoliation of this magnitude since the mid-80s in the county," The Northern Virginia Daily reported.
On May 7, the Forest Service and Shenandoah Countyannouncedthe start of aerial suppression treatments to combat the spongy moth across sections of the George Washington-Jefferson National Forest and adjacent tracts. The application of aerial spray treatments is being periodically conducted using a low-flying specialized helicopter over a 10-day period, contingent upon weather conditions.
The pesticide being deployed is a naturally occurring bacteria called Bacillus thuringiensis var. Kurstaki, or Btk, which in essence destroys the digestive system of the caterpillars in order to curb their appetite. A local district ranger for the George Washington-Jefferson National Forest, Mary Yonce, said the results from the treatments so far appear to be positive.
"It's just a severe, severe infestation," Yonce said. "We don't necessarily have a scoring system for this kind of thing, but based on the information I'm hearing and from what I've seen, it's a very, very severe infestation."
Virginia Department of Agriculture spokesperson Mike Wallace wrote in an email that the Forest Service is treating infested portions of federal lands in and near Shenandoah, Frederick, Warren, Page, Rockingham and Augusta counties.
Scott Salom, an etymology professor at Virginia Tech, said there are any number of reasons for spongy moth outbreaks, but that droughts can be a contributor because the fungal pathogen, or the moth's natural predator, Entomophaga maimaiga, does not do as well under dry conditions. If rainfall is limited and precipitation levels remain low, that generally means a greater volume of eggs laid by spongy moths will survive, leading to possible outbreaks when those eggs hatch.
The Northern Shenandoah Valley endured a severe drought last year, with localities across the region declaring drought emergencies and the Shenandoah National Park temporarily closing its streams and rivers to fishing due to low water levels.
'A bit of a shocker'
Spongy moths first arrived in Virginia in the 1980s. Newspaper headlines— like The Washington Post's 1982 article "So Far Its Gypsy Moth 1, Virginia 0" — chronicle the state's fight to curb the infestation.
Woodland ecosystems in the state have been hard hit in the past, prompting the launch of programs to help slow the spread. In 2000, state forestry officials reported that aerial surveys showed that spongy moth caterpillars had defoliated more than 71,000 acres of woodlands, including 15,200 acres Shenandoah County.
Spongy moth caterpillars have also been detected in the Northern Shenandoah Valley's urban center, Winchester, much to the dismay of city arborist, Jordan Herring. This week, he discovered spongy moth caterpillars in two city parks— Jim Barnett Park in the heart of the city and Harvest Ridge Park near Middle Road.
"It's been a bit of a shocker," Herring said Wednesday, adding that he's waiting on guidance from state environmental agencies on how to proceed. He's hopeful a wet spring will help keep the population down.
"We've always thought of it more as like a forest threat, not as much of an urban threat, although we are now seeing it in the city," Herring said.
It's also a problem in neighboring West Virginia. The West Virginia Division of Forestry characterizes the spongy moth as "potentially the most destructive forest pest threatening West Virginia woodlands," with the ability to spread south and west at a rate of approximately 5 to 10 miles per year.
Over the last decade, it has been spreading across West Virginia's Eastern Panhandle, the West Virginia Division of Forestry says, with the current concentration in nearby Jefferson, Berkeley, Morgan, Hampshire and Hardy counties, among others.
Earlier this month, the West Virginia Department of Agriculture conducted aerial treatments of approximately 25,322 acres to reduce "significant impacts" to forests.
They're everywhere
Living on the scenic eastern slopes of Great North Mountain in western Frederick County, Hall has photographs of spongy moth caterpillars feeding on oak leaves, hanging from a strand of silk/webbing.
He's not the only one in the Shawneeland area who has noticed the creepy, crawly influx. Struck by the sheer volume, numerous people have taken to social media to find out what they are.
Sutphin said people who live in highly infested areas are seeing caterpillars crawling on all surfaces, as well as frass (feces) from the caterpillars dropping from trees and bits of chewed leaves littering the ground underneath infested trees.
Hall said the destruction being wrought by the caterpillars could be costly for some homeowners.
"We have oak trees, and if a tree dies, if it's in danger of falling on the house, we have to spend thousands of dollars to get the dead trees removed, so it's a financial burden, too," Hall said. "... There's a lot of neighbors out here who are facing the same situation, particularly those who have had homes here for some time where there's more of a cabiny-feel."
He also noted that some people have an allergic reaction when they come into contact with a spongy moth caterpillar. According Cornell University's agriculture department, the small hairs on the caterpillars have histamines that can cause an itchy, red rash.
Can anything can be done?
Several pesticides are labeled for use on spongy moths, though many of these products require specialized equipment and a certified pesticide applicator license for application, so working with a certified arborist is highly recommended, the Virginia Department of Agriculture says. Management resources for landowners can be found at: https://dof.virginia.gov/forest-management-health/forest-health/insects-and-diseases/spongy-moth/
Additionally, homeowners on small properties can apply horticultural oil solutions to egg masses to destroy them before they hatch, the Virginia Cooperative Extension says. To protect vulnerable trees, banding with material such as burlap can be used.
Female spongy moths moths lay eggs on many outdoor surfaces — stacked firewood, trailers, grills, lawn furniture and toys. When people move these items to a new location, the spongy moth's eggs also move.
