Get ready. There is every indication that the browntail moth outbreak in Maine this summer may be the worst since the invasive insect arrived in the state 100 years ago. Not only are officials predicting more moths this summer, but the range has also expanded.
Much of the blame for the increase in browntail moth activity in Maine can be attributed to climate change, according to one of the state’s top forest insect experts. Last year’s unusually dry spring conditions combined with warmer than average late fall and early September temperatures created optimum conditions for browntail moth reproduction and dispersal.
“It’s going to be as bad or worse than last year in terms of the browntail moth population,” said Allison Kanoti, state entomologist with the Maine Forest Service. “It’s going to be far worse than [during] the last outbreak in the 1990s and maybe since it arrived here in the early 1900s.”
The current browntail moth outbreak in the state began in 2015. According to Kanoti, outbreaks are declared when browntail moth activity has a major impact on tree defoliation and they can last for multiple years. In 2015 alone, the moth was responsible for more than 10,000 acres of tree defoliation in Maine. There’s no way to tell how long the current outbreak will last.
The last outbreak went from 1999 to 2005. It ended due to a combination of a cool, wet spring and a fungal disease that infected the moths.
According to the Maine Department of Agriculture, Conservation and Forestry browntail moth winter web survey map, the moth webs have now been spotted in all Maine counties. The highest populations of the moth are in Androscoggin, Cumberland, Knox, Lincoln, Sagadahoc and Waldo counties.
“The winter surveys showed a considerable spread,” Kanoti said. “These are overwintering webs and does not mean the larvae survived the winter, but there is no indication they have not and folks need to be on the lookout for browntail moths in places they have not seen them for 100 years.”
Browntail moth caterpillars have poisonous, irritating hairs that can cause a blistery rash similar to poison ivy when people come into contact with them. The hairs also can cause respiratory distress if people breathe them in. The caterpillars typically emerge from their webs in May, but Kanoti said she has already received reports of caterpillar activity this month in Camden, Unity and Bowdoinham.
More browntail moths have also meant an increase in browntail moth damage. Browntails nest and feed on the leaves of oak, poplar, birch and fruit trees. In the late 1990s and early 2000s an outbreak centered around Casco resulted in 10,000 acres of defoliation, according to Kanoti. Aerial surveys of browntail moth damage conducted last summer mapped more than 150,000 acres of defoliation due to moth activity.
Kanoti said there is a statistical relationship between climate conditions and browntail moth populations.
“We had a pretty dry spring last year and that helped contribute to good caterpillar survival,” she said. “So in early July when the mature moths came out, there was a bumper crop.”
The moth’s range expansion in the state is also helped by the fact it can travel great distances — up to 100 miles — from where it emerged from its cocoon. Humans also act as browntail moth transport systems, according to Kanoti.
“We can certainly be the vector,” she said. “If I drive and park my car somewhere where there are mature caterpillars and a few hours later I drive away, there is definitely the potential some got on my car and came with me.”
Even though some early caterpillars have been spotted emerging from webs, Kanoti said it’s not too late for landowners to examine trees for the webs. If any are spotted, there are steps people can take to destroy the webs.
If the webs are low enough to ground, people can clip the web-containing branches and burn them. Those that are too high to safely reach may require the skills of a professional arborist. There are also chemical treatments that can eradicate browntail moth webs.
For anyone going the chemical route, Kanoti recommends calling in professional exterminators.
The current outbreak will come to an end at some point, Kanoti said. But the browntail moth is here to stay and anywhere there are host trees for the moth, there is risk for browntail moth activity and exposure.
“Outbreaks do not last forever and they do collapse eventually,” she said. “But predicting when that will happen is difficult and the browntail moth is not going away — it’s been here for 100 years and it will be here in perpetuity.”