Hemlock Woolly Adelgid

Order: Homoptera

Family: Adelgidae

Latin Name: Adelges tsugae

Common Names: Hemlock Woolly Adelgid


The hemlock woolly adelgid is an invasive insect that can cause foliage loss and death of eastern hemlock trees. When a hemlock stand is infested with hemlock woolly adelgid, 95% of the trees can die within a 4-to-15-year period. Loss of hemlock causes other environmental problems, like the release of carbon stored in hemlock stands, loss of habitat for birds and mammals, and other impacts on forest and aquatic ecosystems. The loss of hemlock also impacts cultural and socioeconomic values.

Life History

The hemlock woolly adelgid was first detected in Nova Scotia in 2017 (in Yarmouth County). It has rapidly spread to other western counties, including Annapolis, Queens, Digby, Kings, Lunenburg, and Shelburne. As nymphs, the aphid-like insects feed on water and nutrients found in hemlock twigs. The hemlock woolly adelgid nymphs settle on the underside of hemlock branches near the base of the needles. As the nymphs grow into adults, they are covered in white, woolly material. Adult hemlock woolly adelgids lay their eggs within this protective wool. When eggs hatch, the crawlers (newborn hemlock woolly adelgids) can spread to other locations by wind, animals, or the human movement of logs or other wood products. There are 2 generations of hemlock woolly adelgids every year.

In Nova Scotia, there are no native predators or diseases that can control hemlock woolly adelgids. Cold winter temperatures (-20˚C or colder) can cause high winter mortality, but populations rebound quickly.

Control Options

To help prevent the spread of hemlock woolly adelgids, you should avoid any movement of live hemlock or hemlock forest products, including firewood.

The Government of Nova Scotia is working closely with the Maritime Hemlock Woolly Adelgid Working Group to protect hemlock trees in the province.

Environment and Climate Change Canada, in partnership with the Government of Nova Scotia, is also administering a 5-year program that involves:

  • selection of high priority hemlock stands on Crown and protected lands (including old growth forests and other important ecological areas)
  • application of tree injection and basal bark pesticide treatments to selected stands
  • outreach work related to protecting hemlock trees on other lands
  • facilitating volunteer and community-based stewardship opportunities to conserve and protect hemlock trees
  • research related to long-term management of hemlock woolly adelgids that includes using biological control measures, like the release of predatory insects, to control hemlock woolly adelgid.

This program includes participation from the Medway Community Forest Cooperative and ongoing consultation with the Assembly of Nova Scotia Mi’kmaq Chiefs.

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