Hemlock Woolly Adelgid Adelges tsugae (Annand) Kingdom: Animalia, Phylum: Arthropoda, Class: Insecta, Order: Homoptera, Family: Adelgidae, Genus: Adelges SAMAB Hemlock Woolly Adelgid Fact Sheet (.pdf)

What is it?

Adelgids are aphid-like insects. The hemlock woolly adelgid is a tiny exotic invasive species that gets its name from its woolly white appearance and because its host is the hemlock tree (Tsugae species). The hemlock woolly adelgid has a complex life cycle and produces two generations per year. Eggs are brownish-orange and wrapped in a white fluffy substance secreted by an adult female. Reddish-brown nymphs (or crawlers) hatch from the eggs and use their thread-like mouthpart to pierce a hemlock branch and suck sap from the branch. These nymphs go through four stages before becoming adults and also wrap themselves with a white, fuzzy covering. Adults are reddish-purple and some have two pairs of wings. The flying adults leave the hemlock in search of a secondary oriental spruce host (which does not occur in the United States). The wingless adults stay on the hemlock host and produce 50-300 eggs. Adults, as well as the nymphs, suck sap from young twigs on hemlock trees and cause the hemlock needles to dry out and drop. This defoliation can cause the hemlock tree to die in only a few years.
Link to more detailed biological information: http://www.fs.fed.us/na/morgantown/fhp/hwa/pdfs/mcclure_hwa.pdf (.pdf, 1.4Mb)

How did it get here?

Adeleges tsugae is native to Asia where it is not a problem to native hemlocks. It 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.

Where is it now?

It lacks natural enemies in North America, so it has since 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). The predicted spread rate is about 20 miles per year and its 2002 range was from South Carolina to New Hampshire.

Click on the thumbnail to view printable map (.pdf, 566 kb) of known occurrences of HWA in the Great Smoky Mountains National Park. Created by Scott Kichman (scott_kichman@nps.gov), June 2003.

What’s being done about it?

To understand more about the problem and what is being done about it, click here.

For more information, see these related links.