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Browntail moth winter webs visible in Camden

By Susan Mustapich | Dec 13, 2019
Photo by: Susan Mustapich Browntail Moth winter webs in a tree across from the Camden Snow Bowl appear small and inconspicuous, but each web can house from 25 to 400 caterpillar larvae.

CAMDEN — A Maine Forest Service specialist confirmed that Browntail moth winter webs can be seen in photographs of trees taken in Camden Dec. 12.

The webs are located on the tips of branches, and on tree tops and are generally constructed from a single leaf wrapped tightly with large amounts of the insect's white silk, according to the Maine Forestry Service. BTM favors fruit and oak trees. The webs can be hard to see at the top of Camden's many mature oak trees, which grow from 60 to over 100 feet in height.

Tom Schmeelk, State Forestry Entomologist, told a full house at the Camden Public Library Dec. 12 that the hydrophobic silk covering the web repels water and like a blanket, insulates the small caterpillar larvae in the leaves. The presentation took place in the Picker Room.

Schmeelk began his presentation with the positive news that the cool, wet weather at the beginning of spring this year stimulated growth of a fungus that killed BTM caterpillars through the year. While wet spring weather is not good for farmers waiting to plant crops, it helps knock down the BTM population, he explained. This die-off was seen in many communities, including Camden, he said.

Professional arborists can help with top down spraying with pesticides or other treatments, he said. The Forestry Service maintains a list of pesticide applicators licensed and certified to treat BTM.

The Forestry Service is just beginning to count BTM winter webs, and expects to complete that process by February, according to Schmeelk. Forestry staff conduct the winter web survey by driving along many roads, through many towns on sunny days. They survey trees while sunlight is shining on them, which highlights the silk wrapped webs. The Forestry Service uses this survey as a factor in developing a BTM risk analysis for towns in the coming season.

When an audience member asked if the webs too high to cut down can be punctured to allow moisture in, Schmeelk said that could help, but the webs are strong to the point that they are not easy to break. By hand, you can "just about break them," he explained.

Another question from the audience was why the caterpillars do not freeze in the winter. Schmeelk explained that the caterpillars contain a natural substance that serves as an antifreeze for the insects. BTM are native to Europe, in areas of similar latitude to Maine, and are adapted to cold winters, he said.

Other questions focused on the use of drones for spraying or clipping off webs and the caterpillar-killing fungus. Schmeelk said technology for this use of drones is not that good yet. The fungus does not harm birds or humans, he said.

He presented an overview of the life-cycle of the invasive pest, known for its destruction of trees and for a rash people get when they come in contact with tiny hairs shed by the caterpillars.

In the spring, as soon as the earliest leaf buds open, the larvae become active and crawl out of their webs to feed on new leaves, according to the State Forestry website. As larvae grow they remain out on leaves, and by late June, are full grown. The caterpillars shed their skin multiple times as they grow. The skin is covered with the tiny, barb-shaped hairs, with a hollow core filled with a toxin. The toxin can remain active for up to three years, long after the caterpillars die or pupate into moths.

In late June, the caterpillars spin cocoons, from which white moths with a brown tails emerge. The furry white moth hair is not toxic, but it can carry the caterpillar hairs, which fill the cocoons. Removing cocoons requires many precautions to prevent contact with skin and from causing the hairs to becoming airborne.

Schmeelk said people most frequently come into contact with BTM toxic hairs when doing yard work, and explained precautions. Wetting down areas before cleaning up the yard can help contain the hairs. Working in the yard after a rain has the same effect. Wearing clothing or special contractor protective gear to cover skin can help prevent the rash, while removing yard debris as well as live caterpillars in reach on structures or trees. Caterpillars can be pressured washed off buildings or sucked up in a wet vac with a HEPA filter, filled with a few inches of soapy water to kill the insect.

When webs, caterpillars or cocoons are removed, they must be soaked in soapy water or burned, Schmeelk said. If left on the ground, the insects will eventually emerge.

In closing, Schmeelk illustrated how BTM surreptitiously hitchhike along with humans. The insect first appeared in the area around Boston, Mass. in the 1890s, and in the 130 years since that time, has traveled up the coast to Midcoast Maine.

Midcoast Maine is considered to be on the periphery of BTM infestation, according to Schmeelk, with coastal areas to the south harder hit by the noxious insect. Sitings of BTM in Bangor indicate that the caterpillar has hitched rides with those who travel from Bangor to the coast. The caterpillar can drop down from trees onto vehicle roofs, or crawl up from the ground onto tires, and nest in the vehicle underbody.

The Maine Forest Service maintains a wealth of information about BTM. A list of pesticide applicators licensed and certified to treat Browntail moths and other tree pests, are available on request by calling (207) 287-2431 or emailing, with information is available on the website.

The silk covering Browntail moth winter webs catchs the light in late afternoon, in tall trees on a side street off of Cobb Road in Camden. (Photo by: Susan Mustapich)
Browntail moth winter webs in tree tops at the intersecton of Cobb Road and Cobb Hill Road consist of oak leaves wrapped in caterpillar silk, and can contain from 20 to 400 larvae. (Photo by: Susan Mustapich)
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Comments (2)
Posted by: Stephen K Carroll | Dec 14, 2019 11:16

Back in the 50's when I was growing up it was not uncommon to see men with long poles, the ends wrapped in rags soaked in kerosene.  They would light these and burn the moths off the trees.  This seems to have cured the problem.  This practice is not unknown to modern scientist. Why is there no mention in this article and why last spring were most people I spoke with unfamiliar with the practice ???

Posted by: ananur forma | Dec 13, 2019 21:30


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