Journeys in ancient and old growth forests

HWA Newsletter

IMG_8247Winter: HWA detection season is here

HWA is most visible in winter and early spring, so watch for the characteristic white woolly masses on the underside of branches when you’re skiing and hiking.

HWA established in Michigan

From an article by Michigan State University Extension:

“An insect responsible for the loss of much of the eastern United States Appalachian region’s hemlock trees has found its way into Michigan. The hemlock woolly adelgid poses a threat to the state’s valuable hemlock stands. A call to action by citizens may be the most realistic path to further detection and control.”

MSU extension is coordinating the eyes on the forest program.

Eastern hemlock project on inaturalist

Inaturalist is a website and app that can be used to record observations of any species. The eastern hemlock project is now on inaturalist.

We’re especially interested in locating old-growth hemlock forests, which should be a priority for management.

We’re also very interested in hemlock hedges, which are important for rearing biocontrol organisms (more on this below).

And we’d like records of hemlock woolly adelgid, particularly near the front of its range expansion, to help fellow naturalists track its progress (please also report HWA to official agencies!).

Seeking hemlock hedges

“Hedges made of hemlock trees with thriving populations of HWA are prime candidates for biocontrol. Why? Because predators are easier to catch on a hedge, making it easier to monitor predator establishment and to collect them in order to introduce them in other locations.”

The NY State Hemlock initiative is seeking hemlock hedges, infested with HWA or not. Outside NY State? Add your hedge to our inaturalist project!

June: HWA is still visible

Although it’s past the optimum detection season, hemlock woolly adelgid (HWA) can still be visible for the next month. Keep an eye out for it when you’re in hemlock stands in southern Ontario

Article in Blazing Star

Here’s an article that provides a good introduction to HWA, with an Ontario focus. PDF can be downloaded here:

HWA map showing Ontario

This is the first map showing HWA detections in and around Ontario. It is up to date for 2015 and we’ll work on a new one incorporating this spring’s data soon. Clearly the Niagara Peninsula is most at threat. However since HWA is carried by birds, Long Point is another area of concern, and the north shore of Lake Ontario may also be at risk. Infestations carried on nursery stock could appear anywhere. CFIA reports that their monitoring didn’t detect HWA in the Niagara Gorge in 2016. Let’s hope for the best, but it could still easily be present in the canopy where it is difficult to detect.

This map of HWA infestation was created using 2012 data from USDA, and 2015 information from PAMINY. Ontario data is from the Canadian Forest Service, and CFIA personal communications.

The map is by county; highlighted counties may be only partially infested. Particularly near the front of HWA expansion this will exaggerate the abundance of HWA – on the other hand, infestations can sometimes go undetected for years which has the opposite result.

HWA winter mortality was high in 2016

Some interesting results from Vermont this spring, where adelgids suffered high mortality despite a relatively warm winter:

“The annual HWA winter mortality study was conducted recently by the Department of Forests, Parks and Recreation (FPR). The results were a bit of a surprise, though they seem to match results from other northeastern states. Many parts of the region seem to be experiencing high winter mortality rates. The four Vermont sites have rates ranging from 93.8 to 99.0 percent…  Theories for why the mortality rate was so high in a mild winter abound. It is always good in these discussions to remember that there is always variability in nature. So, the timing of cold exposure is important. Other important variables seem to include the magnitude and rate of temperature fluctuations. This winter winter certainly had many large temperature swings.”

While the news is encouraging, the article also points out that because of the enormous fecundity of HWA, and two generations per year, even a single adelgid surviving the winter can produce up to 30,000 offspring by the following year.


This newsletter was brought to you by Ancient Forest Exploration & Research. Please forward it to anyone who might be interested.

We’re still looking for high value hemlock forests for our hemlock mapping project, please send us details on mature or old-growth hemlock forests that you know of in southern Ontario.

To learn more about HWA in Ontario go to and to learn more about how and when to monitor for HWA go to

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