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Hemlock Woolly Adelgid

Scientific Name

Adelges tsugae (Annand) (Annand 1928)

Common Name

Hemlock Woolly Adelgid (HWA)

Native To
Date of U.S. Introduction

Discovered on the West Coast in the 1920s, but it is disputed whether this was an introduced or native population; an introduced population was discovered on the East Coast in the 1950s (Havill et al. 2006; Orwig et al. 2003)

Means of Introduction

Accidental (Wallace and Hain 2006)


Destroys Eastern hemlock trees (Tsuga canadensis) (Orwig et al. 2003)

Hemlock Woolly Adelgid
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Hemlock Woolly Adelgid, Adult with wax removed


Michael Montgomery USDA, Forest Service

Find more images


  • ARS Research News - U.S. National Arboretum Offers Solution to Hemlock Woolly Adelgid Pest

    • Feb 23, 2023
    • USDA. Agricultural Research Service.

    • Hemlocks in the U.S. are vulnerable to attack by a small insect called the hemlock woolly adelgid (HWA). This insect looks like tiny cotton balls on the needles of the tree and can kill the trees by feeding on the sap. The adelgid has decimated stands of hemlocks in the eastern U.S. While insecticides and biological control measures can offer some relief, the best way to combat HWA is to develop genetic resistance in the trees.

  • New Manager’s Guide for Controlling Hemlock Woolly Adelgids

    • Sep 24, 2020
    • USDA. FS. Southern Research Station. CompassLive.

    • Forest Service scientists have published a guide synthesizing best practices for controlling these tiny bugs. It promotes a strategy of combining insecticide use with adelgid-eating insects.

Distribution / Maps / Survey Status



Selected Resources

The section below contains highly relevant resources for this species, organized by source.

Federal Government
International Government
State and Local Government