Hemlock Woolly Adelgid (Adelges tsugae)

Invader Type: 



Pest Overview and Identification: 

What does Hemlock Woolly Adelgid look like? Learn here.


Pest Overview

The hemlock woolly adelgid  (HWA), Adelges tsugae, is a tiny insect from east Asia that attacks forest and ornamental hemlock trees. It feeds on young twigs, causing needles to dry out and drop prematurely. Trees may die in four to six years. Some survive, but with sparse foliage, losing value as shelter for wildlife and their ability to shade streams.

HWA was introduced to the United States in the 1920s to the Pacific Northwest, and in the early 1950s to the Washington DC and Richmond, Virginia areas. Since its introduction, HWA has spread throughout the eastern United States via wind, birds, mammals, human activities, and the transport of infected nursery stock, creating an extreme amount of damage to natural stands of hemlock, specifically eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana).  

Hemlock is Vermont’s 7th most common tree. Unless it is kept in check by our cold winters, this insect will have a major impact as it spreads within Vermont.

Reproductive Strategy / Lifecycle: 

To correctly identify and manage for hemlock woolly adelgid, it is important turn learn HWA biology.

Signs and Symptoms of Pest: 

Hemlock woolly adelgid only affects hemlock trees, making identification important. Learn how to identify HWA.

Other pests affect also attack hemlock trees. Learn the signs and symptoms on HWA.




View the most current distribution map of Hemlock Woolly Adelgid  in North America.  Hemlock woolly adelgid was observed in Virginia in the early 1950’s and has now spread from Georgia to Maine. In 2007, it was found on native trees in Vermont for the first time. It is now known to occur in Windham and Bennington Counties.  It has also been detected in Windsor County.