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Hemlock Woolly Adelgid

Photo by Elizabeth Willhite, USDA Forest Service, Bugwood.org

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Common Name: Hemlock woolly adelgid (HWA)
Scientific Name: Adelges tsugae
Origin: Asia


HWA is tiny, less than 1/16″ long, and is dark reddish-brown to purplish-black in color. Its name derives from a white “wool-like” covering called an ovisac on mature egg laying adults.


HWA develops and reproduces on all hemlock species but attacks only Eastern and Carolina hemlocks.


The adelgid causes hemlock decline and mortality within 4-10 years of infestation in its northern range. During the fall and winter months, developing adelgids feed on young twig tissue, including starch reserves critical to the tree’s survival.


Moving bird feeders away from hemlocks, removing infested trees from woodlots, and state quarantines may help to slow the spread, while insecticides and biological controls can be used for local eradication.


The white, woolly ovisacs can be easily identified on the undersides of hemlock branch tips from late fall to early summer.

Distribution: View Map

This species has been discovered in the FL-PRISM

HWA Fact Sheets

The Hemlock Woolly Adelgid in New York State 6 Nov 2014

HWA Insecticide Nov 14

HWA Branching Out May 2014