Hemlock Woolly Adelgid
Early Detection Saves Trees
Overview
Hemlock Woolly Adelgid (HWA) is an invasive insect that threatens eastern hemlock trees. The forest pest feeds at the base of the needles, draining the tree's stored nutrients and gradually weakening it. Without treatment, infested eastern hemlocks become unhealthy, their needles turn gray, and trees can die within 4 to 10 years. HWA has been spreading along the West Michigan coastline for several years, with confirmed infestations in nine counties, including Antrim County. Early detection is crucial—identifying an infestation quickly allows for timely treatment, which can save affected trees and stop the spread into new areas. Thanks to funding from the Michigan Invasive Species Grant Program and the U.S. Forest Service, we are offering free HWA surveys in high-risk areas. To schedule a survey please fill out our survey consent form - linked below.
Winter Surveys
HWA surveys are conducted in the winter for several reasons. The adelgids are most visible in the winter when cooler temperatures trigger feeding activity. As the adelgids feed they secrete a white, waxy substance that forms a round ovisac around them making the tiny insects far easier to see. Additionally, the insects are only mobile in the spring and summer. Winter surveys ensure we're not inadvertently spread HWA from one site to another.
The orange areas featured on the map highlights the areas in which HWA is most likely to occur and therefore is the highest priority area for us to survey. HWA infestations are often found along the coastline where distribution of eastern hemlock trees is most prevalent.
Learn more about the distribution of HWA in Michigan here.
Learn about HWA
Hemlock Woolly Adelgid (HWA) is native to Japan where it feeds on Asian species of hemlock and spruce trees. In its native range HWA is not a major pest issue because Asian hemlock species are fairly resistant to HWA and predatory insects are accustomed to feeding on the adelgids. In North America the Eastern Hemlock tree (Tsuga canadensis) is highly susceptible to HWA attacks in part due to little genetic resistance within the tree and also because of lack of predators. North American spruce tree species are not susceptible to HWA damage.
How do I Identify HWA?
HWA are tiny insects that are difficult to see without magnification. However, as the adelgids feed, they secrete white, fluffy strands of wax from pores on their body. This wax — called an “ovisac” — covers the adelgids, protecting the insects and their eggs from desiccation and natural enemies. The white ovisacs are most visible from late fall through early summer and can be found on the undersides of tree shoots. Their prevalence during the winter months makes this the easiest time of year to spot them. Additionally, adelgids always attach at the base of the needles, where the needle stem connects to the branch.
How do I Identify an Eastern Hemlock tree?
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Location: Found in shaded, moist environments across the northeastern U.S., including parts of the Great Lakes and Appalachian regions.
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Size: Eastern Hemlocks can grow 40–70 feet tall, with some reaching 100 feet. They have straight trunks up to 2 feet in diameter.
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Needles: Soft, flat, dark green needles with two whitish stripes on the underside. They are ¾ to 1 inch long and arranged in two rows along the twig. Needles will connect to the branch via a tiny "stem-like" appendage. (see fig. 4)
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Cones: Small, cylindrical cones, 1–1.5 inches long, hang down from branches and mature in the fall. (see fig. 2)
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Bark: Dark brown or gray, with shallow ridges that become scaly as the tree matures.
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Shape: The tree has a pyramidal or conical shape, with horizontal branches that may droop at the tips.
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HWA Lifecycle
Why are Eastern Hemlock Trees Important?
One of our most beloved evergreens, the eastern hemlock (Tsuga canadensis) is also a critical part of our local ecosystems. Often found along ravines, hillsides, and stream banks, eastern hemlock offer habitat for wildlife and provide shade for streams, effectively lowering stream temperatures and increasing oxygen for fish and other aquatic species. Hemlocks provide aesthetic value and are loved by homeowners. It is estimated that Michigan is home to 170 million eastern hemlock trees.
Fishing
The unique conditions created by hemlock streams are important to many species of fish
About our surveys
CAKE CISMA conducts hemlock surveys on public and private properties. You may submit the digital consent form above or request a PDF to print and mail back to us. Our surveys are free for the 2024-2025 season thanks to grant funding from the Michigan Invasive Species Grant Program and private donations. If you value our work and wish to support us please consider donating to CAKE CISMA.
When we arrive to survey we will call you to let you know we're at your property and to discuss any questions/concerns you may have about hemlock woolly adelgid. No news is good news, if we don't find anything during our surveys we will not contact you unless requested. If we do find a suspected HWA infestation we will collect a sample and send it to the Michigan Department of Agriculture for confirmation. You will be notified if the detection is positive, and CAKE CISMA will serve as a resource for you regarding treatment options. Please DO NOT collect samples yourself. CAKE CISMA staff have the required training and permits to collect and ship invasive species material.