Snow and the Hunt for Invasive Insects

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Maine Forest Service

Snow and the Hunt for Invasive Insects

National Invasive Species Awareness week is February 28 through March 4, but it is not too early to join the efforts to reduce the spread of invasive species.

Whether you can’t get enough of the snow this time of year, or can’t wait for it to go, snow cover can be a surprising assistant in the hunt for invasive forest insects. In advance of National Invasive Species Awareness Week we ask you to join the hunt for these serious forest pests and let us know if you suspect you have found evidence of their spread.

Emerald Ash Borer

Late in 2021, Maine Bureau of Parks and Lands Forest Engineer Stephen Richardson was walking the Mayall Mills site on Pineland Public Land in Gray when he noticed ash tree bark scattered on the snow. Stephen figured out that the bark came from ash trees that had drawn the attention of foraging woodpeckers. The ash trees nearby showed signs frequently referred to as ‘blonding’, which appears when woodpeckers remove the outer bark of trees in search of beetle larvae and other meals. When blonding occurs in ash (Fraxinus spp.), it is often evidence of emerald ash borer presence. Stephen reported this observation to the Maine Forest Service, and in this case, emerald ash borer was confirmed. You can learn more tips for recognizing blonding caused by emerald ash borer in this video.

Emerald ash borer has been detected in two distinct areas of Maine; in Southern Maine the infestation is on the leading edge of a large infested area in Cumberland, Southern Oxford and York Counties. In northern Maine, EAB populations are found in only four towns along the St. John River in Northern Aroostook County, and appears to have spread from a spot infestation centered on Edmundston, New Brunswick, Canada. 

Ash bark on snow

A pile of ash tree bark on snow can be a tip-off to the presence of emerald ash borer. Light patches of bark and the bark pile result from woodpeckers foraging for emerald ash borer. Image Credit: Patrican, CC BY-SA, via Wikimedia Commons.

Hemlock Woolly Adelgid

Maine Forest Service Entomology Technician Wayne Searles has been on the hunt for hemlock woolly adelgid (HWA) for more than 20 years. He was the first to identify the insect in Maine’s Forests in 2003 in Kittery and has continued to turn up new infestations in the course of his annual survey work. One of the things we know about HWA is that infestations in the forest most often start near the tops of hemlock trees. When Wayne is helping others learn how to look for this insect, he tells them to look up and down. Porcupines, squirrels, birds and abrasion can cause hemlock twigs to drop from the upper canopy. Those twigs contrast with snow and provide a great opportunity to inspect these fallen upper branches for HWA. You can learn more tips from Wayne in the video featured at the top of this page.

Hemlock woolly adelgid has been found in forests of Maine from Kittery to Mount Desert and inland to Sebago Lake area. Its populations were experiencing a boom over the last couple of years due to mild winter weather. It takes just one hemlock woolly adelgid, carried to a hemlock by wind, birds or other means, to start an infestation in a new location. We suspect the population boom could have led to undetected spread of hemlock woolly adelgid further in to Maine’s forests. 

Hemlock branch with hemlock woolly adelgid, on snow.

Examine hemlock twigs littering the surface of the snow for the tell-tale white fluff that is evidence of hemlock woolly adelgid. Image Credit: K. Coluzzi, ME DACF.

How Can You Help?

When you are out in the forests this winter, watch the snow and the trees for signs of invasive forest pests. If you think you have seen evidence of them in a new location, please let us know. You can report them on our on-line form, by email to or by calling (207) 287-2431.

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