Michigan’s Invasive Hemlock Woolly Adelgid Is Best Detected in the Wintertime

Lizzy Rosenberg - Author

Dec. 2 2022, Published 12:40 p.m. ET

Hemlock Woolly Adelgid Infestation
Source: iStock

Hemlock woolly adelgid infestation on underside of eastern hemlock branch.

Trees are an integral part of our planet. As one of our greatest natural resources for carbon sequestration, they're doing everything they can to curb the ongoing climate crisis. They also play a leading role in regional and micro ecosystems alike. That's why it's important to know about tree-killing invasive species that put our planet's trees in jeopardy.

Michigan is battling the invasive hemlock wooly adelgid — and detecting them is easiest in the winter time.

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Knowing about them and where they come from is crucial.

"‘Tis the season for helping Michigan keep a tree-killing invasive pest at bay," Emily Bingham of MLive writes. "The Michigan Department of Natural Resources and Agriculture and Rural Development are encouraging people to keep an eye out this winter for signs of the hemlock woolly adelgid: a tiny, aphid-like insect that can cause significant harm to Michigan’s estimated 170 million hemlock trees."

"Survey crews from several invasive species management areas will be looking for signs of the hemlock woolly adelgid this winter," Bingham continued. "... property owners with eastern hemlock trees on their land, as well as anyone who spends time outdoors hunting, hiking and the like, are encouraged to help by doing the same."

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Dead Hemlocks
Source: iStock

What is the hemlock woolly adelgid, and how can you detect it?

Michigan's Department of Natural Resources is encouraging local residents to check the the trees in their yard for the presence of a highly invasive species, known as the hemlock woolly adelgid. Because the small insects feed on the trees' nutrients in the wintertime, now is the best time to identify an infestation, according to Click On Detroit.

If they aren't quickly identified, these non-native, soft-bodied nuissances can cause irreversible damage to Michigan's 170 million hemlocks.

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“Cooler temperatures trigger feeding activity,” Robert Miller, MDARD’s invasive species prevention and response specialist explained via Click On Detroit. “As hemlock woolly adelgids feed, they secrete a white, waxy material that creates ovisacs. The presence of these small, round, white masses makes it possible to identify infested trees.”

Thus far, hemlock woolly adelgid infestations have been confirmed across at least five counties in the state.

Crews will conduct surveys along the 5-mile border of Lake Michigan's shore, and all hemlocks will be tagged for future insecticide treatment.

If you aren't sure if you have hemlocks on your property, they generally grow in moist soil along bodies of water, in parks, and in residential areas. They have flat green needles, can grow up to 75 feet tall, and have willowing branches. The adelgids will show up as little white cotton-like balls on the underside of the branches.

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Hemlock Infestation
Source: iStock

How did the hemlock woolly adelgid come to the U.S.?

The hemlock woolly adelgid hails from East Asia, according to Michigan's state government website. It's unclear how they made their way to the U.S., but it was likely due to plant or crop transportation.

The pests have been found across upwards of 20 U.S. states, so Michigan isn't the only one. But they are infecting Michigan's hemlock trees on a serious level.

As we know, invasive species tend to spread as global warming continues — so pests like these will likely continue to pop up as temperatures keep rising.

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