The 1,000-Mile Great Lakes Adventures

Wednesday, February 24, 2021

Hemlock Wooly Adelgid


Loreen Niewenhuis is an author, adventurer, and dynamic speaker. 

She has completed a trilogy of 1,000-mile journeys exploring the Great Lakes and has authored three books about these adventures. 

To learn more about her work, or to engage her as a speaker, go to

There is an invasive species that has been decimating hemlock trees in America for decades. It is a small insect similar to an aphid called the wooly adelgid.
This insect is native to Asia and made its way to America via imported plants in the 1950s. It has  been slowly spreading for decades and has made its way to northern Michigan. This pest has recently been found in Sleeping Bear Dunes National Lakeshore. 

I often hike in and around Sleeping Bear Dunes and have seen many mature hemlock trees in these forests.

One of my favorite hikes is at the Traverse City Commons, and there are some massive hemlocks there. 

Check out the view from the wooded dunes:

There is a hemlock that I visit there, and after the recent storms, I was sorry to see it had developed a crack in the trunk. 

These trees are the preferred feast for the wooly adelgid. They congregate on the underside of the needles and suck the sap out of the tree. The needles turn brown and new growth is inhibited. Infested trees can die within 4-10 years.

Trees can be treated with pesticide and can be saved if infestation is caught early.

Severe winters helped to slow the spread of this pest.

Update (info from NPS):  Though the tiny insects don’t move far on their own, they can be blown by wind or hitchhike on birds or mammals – including humans - that come into contact with an infested branch. In a similar way, cars, boats, tents, or RVs parked under infested trees may be able to transport the insects to new locations.

So, clean your boots and NEVER transport wood from one area to another.

1 comment:

  1. Can you give hikers any advice on how to ensure that they don't inadvertently spread this pest?