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Photo credit yourwildcity.com, Maris Wicks, and Rosemary Mosco

Winter Moth Mayhem

A total eclipse of a moth

Winter moth caterpillar © Milan Zubrik, Forest Research Institute, Slovakia, Bugwood.org
Winter moth © Robert Childs, University of Massachusetts, Bugwood.org

It may be difficult to remember now, but last spring was a boon for many species. You may recall that there was much talk about the often maligned Eastern Tent Caterpillar (ETC) and their defoliation of our black cherry trees and beach plums. In other parts of Massachusetts, an even bigger problem was bearing down on the forests; winter moths.

Winter moth caterpillars emerge from eggs around the same time as the ETC, early May. However, these little caterpillars, often called inchworms (see photo to the right), are a non-native species originating from Europe. Winter moth caterpillars produce strands of silk which enable them to travel on the wind from one tree to another in a behavior known as ballooning. Spring 2015 was a robust year for winter moths. They decimated certain eastern forests denuding many trees and shrubs. While I am a fan of the native ETC and encouraged readers not to worry about one or two boom years, it is a different story with the winter moth. As a non-native, these creatures feed on a wide variety of host plants causing a lot more overall damage than the much more specific, and native, ETC. According to Massachusetts Audubon, winter moths affect maple, oak, ash, and fruit producers such as apple, crabapple, and blueberry.

So why post an article about these spring caterpillars now? Because many of us on Nantucket are just now noticing the adults. Winter moths have been lying in wait since late May. They pupate in the ground and emerge in, you guessed it, winter (typically November or December). Many people have begun noticing the sudden scourge of tiny gray moths at their front porch lights and back decks. While some have speculated on the warm fall as a cause, it seems that it is a delayed effect of the crazy spring caterpillar season we had.

What we are seeing now are the adult males emerging and flying around looking for females. Females, who cannot fly, release pheromones to attract males. After mating, the females will crawl up tree trunks and lay eggs that hatch in early spring.

It is not clear why the winter moth population has grown so quickly. It was introduced to the US in the 1970’s and only recently has its populations exploded. The same record numbers were seen in 2015 in Connecticut, Rhode Island, and Massachusetts. Some speculate that the snow pack from last year, which lasted until almost April in some places, may have been a factor.

A robust winter moth population in 2015 is a good indication that spring 2016 may also be a banner year for winter moths. Let’s just hope the conditions this winter hinder rather than help this invasive species.

So, what to do about Winter Moths? University of Rhode Island researcher Heather Faubert who studies winter moths says using sticky tree bands can be an effective method that reduced the use of chemicals.

“I’ve been putting up tree bands for several years,” she said. “The reason I do it is because it congregates the eggs. The females climb up the trunks and they encounter the tree band, and they just sort of stop there and lay a bunch of eggs.” The homeowner can then scrape off eggs or use dormant oil in a targeted location on the tree trunk.

With the eggs clustered below the band rather than high up on the tree, Faubert is able to monitor them and see when they hatch.

On the mainland, authorities have been testing a biocontrol for the moth using parasitic flies that attack the caterpillars. While this method has been successful in Nova Scotia, but is still being investigated in the US.

For more information, check out this useful winter moth identification and management fact sheet created by the UMASS Extention program.

You can even help state scientists by reporting sightings for Massachusetts here.