Brown Tail Moth Outbreak Makes Life Itchy for Maine Farmers

As daylight hours lengthen and temperatures begin to warm, you might notice something fluttering in the tops of the still-bare trees around Maine. It’s the silvery, silky nests of the brown tail moth (Euproctis chrysorrhoea) flashing in the sunlight among the budding branches. The caterpillars are brown, with a white stripe down either side of their bodies and two red dots on their backs. In their larval stage, the brown tail moths build nests of webbing and dead leaves in which to overwinter. They emerge tiny and hungry in April, just as the trees begin to leaf out. Capable of decimating entire orchards, the caterpillar continues to eat and grow until June, when they transform into little white moths.

The caterpillars do not just destroy trees. They can do damage to people as well, thanks to the minuscule white hairs that they shed, blowing in the wind or remaining after the caterpillars have departed. The rash can arrive after picking up branches or leaves with moth hairs in them or simply by being outside near an infested tree on a breezy day. The red welts of the rash itch and burn and, unlike poison ivy, the bumps can grow to the size of a dime. The itching and burning can last for more than a week. In some cases, the hairs of the caterpillars can cause respiratory distress, and if you have pre-existing respiratory issues, these can be extremely serious. For farm workers, foresters and anyone laboring outside in Maine, this is one of the hazards of the job.  

Brown tail moths first arrived in the US in the late 19th century by way of Cape Cod. For nearly twenty years, the population exploded across New England, Quebec and the Tri-State area. However, the introduction of a parasitoid fungus and aggressive applications of obsolete sprays such as arsenate of lead brought the population under control by the 1920s. Minor outbreaks would occur throughout the 20th century. The parasitoid fungus, entomopohaga aulica, thrived in the cool, wet New England weather, keeping the moth population under control until 2015, when an outbreak began along the Maine coast. This outbreak has stayed largely within the state, which has entomologist Tom Schmeelk, of the Maine Forest Service perplexed. “There hasn’t been a clear definitive answer for why it has not expanded back to its reach in the early 1900s.”

However, it is suspected that Maine’s increasingly warm and dry spring weather has played a role. The fungus that proved so effective at controlling the moths naturally in years past requires a cool, wet spring to thrive. The moth larvae thrive on warmer and drier conditions, and Maine has suffered moderate to severe droughts since 2015. With no natural agents to combat them, the brown tail moths have thrived.  

When Sarah Pike purchased Tops’l Farm in Waldoboro, ME, in 2015, she had  a vision of a glamping getaway and farm destination. What she didn’t know was that many of the beautiful apple trees lining the property’s walk to the Medomak River had already succumbed to brown tail moth infestation. “Losing many of the ancient apple trees on the farm within the first few months of our stewardship to the brown tail moth, felt like the property lost a really important part of its story.”

Pike began to combat the moths. She attempted spraying the apple trees and tall oaks that surrounded her farm, but the moths kept returning. Eventually, Pike began a regimen of daily nest clipping and caterpillar squishing. The most effective way to combat the moths is by clipping their nests out in late fall or early spring, when the caterpillars are dormant and the nests are most noticeable. Barrier bands around tree trunks can also prevent caterpillars from attacking a tree, as long as any existing nests are thoroughly removed.

A tree after brown tail moths devoured it. Photography courtesy of the author.

While brown tail moths are generalists, they do seem to prefer fruit trees and oak trees, putting a strain on Maine orchards. Bob Sewall is the steward of Sewall Organic Orchard, the oldest organic orchard in the state. Sewall has been tending his orchard for more than forty years. Brown tail moth caterpillars first began to appear in his trees four years ago, and he quickly found them to be more destructive and persistent than any pest he had faced before. Having never sprayed his trees, his first focus was to prune the larval clusters out.

“We took over 1,200 nests out,” Sewall says. “And we still didn’t get them all.  It was a losing battle; if you miss one nest, that can defoliate an entire tree.”  

Fortunately for Sewall and Pike, sprays are available that are effective against the moths. Sewall uses a combination of BT and Entrust organic insecticide, and he now sprays his orchard twice a year with this mix. But spraying is ineffective in a 65-foot-tall oak tree, and the moth population across the state continues to grow.

While some urban towns have organized volunteer efforts to clip out the moth nests on town property, the battle against brown tail moths has been left largely in the hands of individual landowners. In a state covered in majestic, old-growth trees that reach up to the sky, clipping and spraying both require a tree crane, which has greatly hampered individuals’ efforts to fight the outbreak. The Maine Forest Service suggests that if hiring a crane is cost prohibitive, a collection of neighbors might combine resources to have their area treated, but such co-operation does not always occur.  

While Maine scientists hope for a natural decrease in the moth’s population, they are also working on other mitigation methods, such as the release of the female sex pheromone, which confuses the males and disrupts the mating cycle. “This would be highly specific to the brown tail moth, so no non-target effects on beneficial insects,” says University of Maine Forest Entomologist Angela Mech. “It is eco-friendly and has the potential to be highly effective for a large area.”

While we wait for new mitigation methods or a return of the moth killing fungus, Mainers will continue to suffer from the brown tail moth rash. Long sleeves and limiting outdoor time can help reduce the risks of the rash developing, but for farmers who have to be outside every day and often work directly in moth-infested areas, topical ointments and sprays are available that specifically treat the brown tail moth rash and can provide relief.  

“We are still in an outbreak,” Mech says. “We will be itchy this summer.”