top of page


Updated: Feb 24, 2022

The hemlock woolly adelgid (HWA) is an invasive insect native to Japan and the Pacific Northwest that has been destroying hemlock pine trees (their primary food source) throughout the US for decades. It was introduced to the US by accident in 1951, and has since spread to western and eastern regions. Most recently, HWAs have been spotted in western New York, including the Finger Lakes and Adirondack regions.

The New York Department of Environmental Conservation (DEC) is asking anyone who notices signs of HWA infestation to take action in stopping them.


If left unchecked, HWA populations have the power to disrupt ecosystems throughout the US by eliminating many species of animals and plants that depend on hemlocks for their survival.

  • They provide food, shelter, and protection to animals including moose, black bears, salamanders, and migrating birds.

  • Unique species of lichen and other plants also depend on the shade and root systems of hemlocks to provide ideal growing conditions.

  • Their roots are able to grow on steep slopes which helps prevent soil erosion.

  • Shade from their dense canopies help manage the temperatures of streams and rivers, which is essential for fauna that lives in cold water such as trout.

By helping fight the threat of HWA infestations, we can save entire ecosystems that depend on hemlock trees to thrive. Read on to learn how to take action.


Woolly adelgids are about as small as grains of rice, which can make it difficult to spot. The easiest way to find HWAs is to look closely around the base of needles for their trademark white wooly masses that form as they feed from the tree’s nutrients. Branch dieback and gray needles are also key indicators of an HWA infestation.

If there are hemlock pines in your neighborhood and/or parks, look for the following signs of infestation to help save your local ecosystems:

  • Fuzzy white specks the size of grains of rice located around the base of hemlock needles,

  • Gray-tinted needles

  • Needle loss and branch dieback


Young HWAs attach themselves to hemlock branches at the base of needles to feed from the tree’s starches, disrupting its flow of nutrients to the canopy, and turning its branches and needles gray as they begin to die. They remain in the spot they attach to for their entire lives, and kill hemlocks about 4-5 years from the date of infestation.

How You Can Help Stop the Woolly Adelgid

Reporting a sighting to the DEC is the best way to stop the spread of woolly adelgids, and receive help with treating the HWA infestation. Here’s how you can help stop HWAs from continuing to kill and invade our forests:

  1. Take pictures of any signs of infestation as outlined above. Place something in frame for scale like a ruler.

  2. Write down the location of infestation, and include details such as nearby roadways and landmarks. If you can, GPS coordinates are the most helpful.

  3. Email your photos and location details to DEC Forest Health at You can also call the Forest Health Information Line at 1-866-640-0652.

If you see signs of an HWA infestation, the DEC urges you to take immediate action. You may have spotted them in a town or ecosystem where it hasn’t been recorded before, which is vital to the DEC’s efforts to track and manage HWA populations. Reporting your sightings also may help save the ecosystems in your area, as treating a HWA infestation can save the many species of animals and plants that depend on them to survive.

HWA Treatments for Hemlock Infestations

There are both natural and chemical treatments available for those ready to take action against HWA infestations.

Natural Woolly Hemlock Adelgid Treatment

There is a species of beetle called the Sasajiscymnus tsugae (St) that is a natural predator of the HWA. It eats woolly adelgids at each stage of its lifestyle. If there are hemlocks on your property that are infested with HWAs, you can purchase these beetles from to introduce them into your ecosystem.

Sasajiscymnus tsugae beetles provide a long-term solution to hemlock infestations, and are much less harmful to the surrounding environment than most chemical treatments (with the exception of those endorsed by the DEC).

Note: Do not introduce this beetle to hemlocks that are not on your property. If you find a hemlock infestation on public land such as a park or national forest, consult with your local national parks services before starting biological or chemical treatment.

Chemical HWA Treatments

Chemical insecticides including Imidacloprid and Dinotefuran have been shown to be the most effective at killing hemlock woolly adelgids. It is important to note that these chemicals must be applied by a licensed pesticide applicator. Doing so on one’s own can be dangerous, and can harm the surrounding wildlife if done incorrectly.

If the DEC confirms that you found woolly adelgids, visit the Hemlock Initiative website for information on how to treat HWA infestations. It is crucial that your sightings are reported and confirmed by the DEC before you begin any treatment.

The DEC needs to know of any HWA sightings in areas where they haven’t been spotted before to help with their conservation efforts. They can also give you directions for properly treating hemlocks so as not to harm the surrounding environment.

More Info On Invasive Species & How You Can Help

IDEA Collective believes that the biggest changes in environmental conservation start at the local level. To learn more about how to protect your community from invasive species, check out our Asian Longhorn Beetle Invasive Species Kit, designed to teach kids about invasive species with creative STEAM learning activities and puzzles!

39 views0 comments

Recent Posts

See All

Keep up to date with new activities, and join our list!

Thanks for submitting!

bottom of page