This story was originally published in January 2021.
Browntail moths, which can cause allergic relations in humans due to their toxic tiny hairs, have settled into nests high up in leafless trees for the winter. And that, experts say, is why now is the perfect time to check for browntail moth webs.
The moths are particularly attracted to apple and oak trees, constructing their webs in the fall on the highest branches.
The invasive browntail moth has been steadily moving northward in Maine following the coast since it was introduced in Massachusetts in the late 1800s. Along the way it’s been defoliating trees and causing mild to severe public health issues.
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. They have deemed a public health nuisance by the state and as far as Jim Dill, pest management specialist with University of Maine Cooperative Extension, is concerned, the only good browntail moth is a dead browntail moth.
If you do detect any of the nests on your trees, those same experts recommend forming a plan to kill them now or before the trees’ buds open up in the spring.
“Their webs are really well built so they can survive in the cold weather,” said Derek Legassie, owner of Ground Renovators, a tree health care service based in Holden. “Looking up at your trees right now you think it’s a leaf on top, but [the cocoons] have a sheen when the sun hits them in the morning this time of year, so now is the time to look because they really stand out.”
In the spring, the larvae crawl out of the webs to feed on new leaves, Dill said, and by late June they are fully grown. That’s when the caterpillars spin rough cocoons in which they pupate, and from which they emerge as moths in July.
Depending on where you spot the nests and how high up they are, you have options to get rid of them, Dill said.
“When you think of the difference in size between an apple and oak tree there can be quite a difference how high the nests are,” Dill said. “If you see them in an apple tree, you can probably reach them with a good sized stepladder, versus an oak tree, they can be 50 feet or more above you.”
That’s where professionals like Legassie can help.
“When they are up so high and you try to trim off the branches with nests you can reach, you are probably going to miss a nest or two,” Legassie said. “Even if you miss one nest, you have missed 150 to 200 caterpillars.”
Arborists or tree health companies like Legassie’s have specialized equipment and machinery that can lift them up to those highest branches to get every nest.
Another option is to identify any tree with nests and arrange for someone like Legassie to come in the spring to inject the tree near its base with a chemical that rises with the tree’s sap up to the new buds and leaves on which the emerging caterpillars will feed.
“It’s like putting an IV port into the tree,” Legassie said. “It only takes a very small amount of liquid.”
That chemical treatment does not harm the tree or any insects and other creatures who feed on its flowers later in the spring, Legassie said.
Calling in professionals can run hundreds of dollars per tree, Legassie said, but that is often less costly than the removal fees associated with a tree that has to come down or has fallen down due to browntail moth defoliation.
“They can really do a number on your trees,” Dill said. “With all those caterpillars around you have to deal with those toxic hairs and anyone who has had the rash or respiratory issues from coming in contact with those hairs will tell you it’s worth almost any amount of money to get rid of them.”