Maine's Trees: The Hemlock Tree and its Arch-Nemesis, HWA
May 17, 2021
The hemlock tree (Tsuga canadensis) is a very important component of Maine's forests as it provides critical habitat for a number of Maine's wildlife species, e.g. white-tailed deer, and provides important shade and cooling for fish in streams and rivers. It is a valued timber tree and often grows 60-70 feet high. In 1999, the hemlock woolly adelgid (HWA), a tiny sap-sucking insect, arrived in Maine on hemlock nursery stock. In 2003, populations resulting from natural spread from Southern New England were detected in Kittery's forests. HWA is now found in over 40 towns in 5 Maine counties.
- Learn how to recognize and report HWA. "Hems have stems!" Hemlock trees are one of a few conifers in the state that can be distinguished from pines, fir, and spruce by short needles that attach to the twigs with stems (instead of suction cups). HWA are extremely tiny and feed at the base of these short needles. At certain times of year, you can see white woolly balls made by the feeding insects underneath. If you live outside the known infested area and you see this, report here.
Take a Stand! Volunteer to "Take a Stand for Hemlocks". Adopt a hemlock stand and survey it annually for the presence of hemlock woolly adelgid. Participants are trained to identify HWA and to apply these detection and monitoring survey methods developed. Learn more.
Are you a schoolteacher, or need a K-12 project? The Gulf of Maine Research Institute has an investigative mission for hemlock woolly adelgid!
Time your tending! If you have work to do in hemlocks, try to time it for when HWA is harder to move. HWA cannot survive on cut hemlock branches from around August through February. The only life-stages that can survive off of rooted hemlock are the eggs and crawlers. Those are abundant from late-winter through early-summer.
Spread awareness and celebrate the state's trees. Take your National Invasive Species Awareness Week commitment beyond this week. Tell your friends, family, neighbors and others about invasive species! It's a big state, and we can't get the word out to everyone without your help. Encourage them to get involved with National Invasive Species Awareness Week in their own way. Here are some resources to help get started: