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Browntail Moth: Act Now!

Harpswell Heritage Land Trust
March 5, 2019

By Kyle Rosenberg, local arborist and plant enthusiast

While Ole’ Man Winter had his accomplice, Boreas, sweep down from the north with bitter cold this winter, I know that March is closely followed by the budding of spring. As I look out the window at 5:30 p.m. this 28th day of February, it is clear the days are getting a tad longer, the sun’s rays a bit warmer and the anticipated changing of the guard, so to speak, is beginning.

With the warmer days come the flowing sugar maple sap and a liquid sweet delight boiled down in the sap houses all over the state. The orchardists, armed with snips, pruners and saws strike out into the fields to prune their fruit trees. And we begin to scan our trees for what looks like tufts of wadded tissue paper squeezed by the fistful onto the ends of tree branches.

A Browntail moth nest (Kyle Rosenberg photo)

Our oak, apple, cherry, pear, shadblow, hawthorn and even shagbark hickory trees hold the overwintering nests of the now infamous Browntail moth (BTM for short). The wads of tissue paper, which are actually leaves lashed together with silk, are a perfect, weathertight home for 50-400 overwintering baby BTM caterpillars.

For those who have not yet taken it upon themselves to act, the warmer days of March and April provide a window of time where management of BTM is quite effective. Like the orchardists in the fields, homeowners are now gearing up to seek out and remove BTM nests from the tree branches they are able to reach. Even the nests in the tallest oak trees can be pruned with the help of a Maine Licensed Arborist.

Once cut from the trees, nests may be soaked in soapy water and thrown away. Or, for a more rewarding experience, one may gather together a pile of sticks, kerosene and a match to torch the nests upon the backyard funeral pyre.

Before long we will see the boldest of cornelian cherry and daffodil in the landscape and winter pruning for BTM will come to an end. By the first of May, forsythia, magnolia and maple trees are flowering. BTM caterpillars leave their nests seeking out food. Since buds at the ends of the branches tend to open first, BTM nests are ideally placed to give the newly emerging caterpillars a ready meal.

Initially the ‘babies’ stay close to the nest. They venture out by day, leaving behind a ‘silk road’ for others to follow and to lead them back to the nest at night, where they must cuddle together to stay warm.

Once the temps become more favorable, in late April or early May, and the caterpillars a bit bolder, groups may be found at the bottom of branches in the morning and disperse during the day. As more buds begin opening, the caterpillars spread out in search of the food necessary to complete this stage of their life cycle. Those who know the drill know that now is the time when spraying for BTM is ramping up.

As the weather warms in mid May, around the time the horse chestnut trees are flowering, the caterpillar feeding has led to rapid growth and development. As the caterpillars molt, shedding their old shell for a new one, they begin to produce small toxic barbed hairs that cause itchy rashes to those of us susceptible. Usually by the time their feeding damage is easily spotted from the ground, the caterpillars are of a size where the toxic hairs have developed.

The hairs of BTM cause a rash similar to the irritation one may suffer from exposure to fiberglass insulation. The itching can last one to seven days or more in some cases. Respiratory irritation occurs in some people. There are a number of over-the-counter remedies to sooth the itch of the BTM rash. Such remedies touting relief are hydrocortisone, witch hazel, Aspercreme/Sarna mix, calamine lotion and tea tree oil. Many pharmacies in the greater Bath-Brunswick area have produced sprays to help alleviate symptoms.

Like many things in life, by the time you have discovered where your odd rash came from, the culprits are beginning to flee the scene. By mid June, the fully grown caterpillars are beginning to look for safe spots to build cocoons for their transition from caterpillar to moth. These cocoons contain the highest concentrations of toxic hairs! Many caterpillars decide to knit a few leaves together and pupate between them and these structures can be confused with an old nest. When folks try to rip them out of the trees by hand, there can be unpleasant consequences.

Coming back to the present time, now is the time to be inspecting your trees and snipping where you are able. Act now! The Maine Forest Service provides more information about BTM and a list of licensed contractors who are able to help spray infested trees during the caterpillar stage of BTM. Now is the time to call if you require help. The impacts of BTM are widespread and the list of service providers is short.