Hemlock Woolly Adelgid (HWA)

The Hemlock Wooly Adelgid is a tiny, aphid-like insect that has been killing North American hemlock forests since the 1950s. It has been moving slowly northward, becoming adapted to colder climates. HWA was found in the Finger Lakes in the early 2000s.

When HWA settles on a hemlock (blown by the wind, carried on clothing, fur, or feathers), it inserts a long feeding tube into the hemlock twig. When enough adelgids are present, the tree responds by shutting down food to the twig, killing the buds, needles, and finally the tree. From beginning to end, the process can take six to twenty years in New York.

Hemlocks are some of the largest and most beautiful trees in the Finger Lakes forest. Because they are shade tolerant, they often grow in gullies and help to stabilize slopes, support unique indigenous assemblies of plants and animals, and keep water and homes cool and shady.

What Is HWA?

The Hemlock Woolly Adelgid (Adelges tsugae) is a small (less than 1/16”) invasive pest that can often be found on the underside of hemlock needles, where it sucks out starches from the tree. They multiply and spread incredibly quickly and can take over an entire tree. Tree health declines and mortality usually occurs within 4 to 10 years.

What Damage Does it Cause?

HWA has the ability to attack and kill hemlock trees in a matter of a few years, posing a significant threat to the structure of our watershed gullies, the beauty of our lakeside properties, and ultimately, the water quality of our Lakes.

Why Do We Care?

Eastern Hemlocks (Tsuga canadensis) have been occupying Finger Lake gullies for more than ten thousand years since the last glaciers retreated. The recent discovery of the invasive forest pest Hemlock Woolly Adelgid (HWA) in our watersheds is a reminder of what an important role hemlocks play in our ecosystems.

Known Locations of HWA Infestation in New York

HWA has caused considerable damage to hemlocks on Long Island, in the Lower Hudson region, and southern Catskills. Infestations have been found throughout the Finger Lakes region and in 2017 the first HWA sighting in the Adirondacks was reported. In 2020, HWA was found in Fulton County. Through research, management, and help from community scientists, we hope to slow the spread of HWA, reduce its impact, and implement an effective biocontrol management strategy.

Fact Sheets and Treatment Resources

Learn how to survey for HWA

You can contribute to the fight against HWA & save our Hemlock trees!

Learn how to identify and report HWA sightings in a few simple steps!

Step 1: Download the iMapInvasives App for your smartphone and select “Hemlock Woolly Adelgid” as the species. Be sure to select the “Finger Lakes HWA Volunteer Survey Project”.              Project Instructions

Project InstructionsStep 2: Look for Eastern Hemlock in or near gullies or on steep slopes, where their tenacious root structure holds highly erodible soils in place.

  • White woolly masses around the body of the insect
  • Woolly masses are clumped on twigs near the base of the hemlock needle
  • Needle loss and branch dieback
  • Grayish cast to trees, rather than a healthy deep green

Step 3: Snap a picture of suspected HWA, and submit using the iMapInvasives Mobile App! The app records your GPS coordinates and will map the occurrence of HWA to help direct management efforts in the future.

Canandaigua Hemlock Stands

HWA Survey Assistance Form
CLWA is offering survey assistance to property owners that have hemlock trees. At the request of the property owner, a CLWA volunteer trained in identifying and reporting hemlock woolly adelgid will visit the site to scout for signs of HWA. Data collected will be submitted with statewide researchers, and used to help prioritize HWA management strategies in the Canandaigua Lake watershed in the future. Property owners may use the form below to request a survey, and CLWA will be in contact with you to arrange a time for a site visit.

Additional Resources