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Hemlock Woolly Adelgid

Posted on Feb 12, 2014

Hi there! For those of you that don’t know me, I am an Eastern Hemlock tree (Tsuga canadensis). I am a native tree that grows in the eastern part of the United States and Canada, and because of my size I am sometimes referred to as the “Redwood of the East.” I can reach upwards of 30 meters or roughly 100 feet in height and can live to be 800 or more years old. I have short, flat needles and long branches that reach up to the canopy and sweep down to the forest floor, creating unique micro-habitats for other species to utilize. Not to sound boastful, but I am a very valuable tree because of all the shade I create and preference several species have for me, and that’s no duff! For example, all the organic litter beneath my branches is a great place where over 200 species of invertebrates may reside. I create cool spots in streams where my branches overhang, allowing for higher concentrations of dissolved oxygen, which several cold water fish species such as trout prefer as well. Blackburnian and Magnolia Warblers prefer coniferous stands and will glean insects from the undersides of my needles, while a number of other bird species will find refuge underneath my branches on the ground.

Healthy Hemlock Tree

Unfortunately, I have one kind of species that benefits from my kind, but I do not like it. It calls itself the Hemlock Woolly Adelgid (Adelges tsugae), or HWA for short, and it was brought to the United States in the 1950’s all the way from Asia. HWA is an aphid-like insect that has sucking mouth parts and feeds off the nutrients within a Hemlock’s twigs. Throughout June, adult females will lay 10 to 300 eggs. Once the nymphs or “crawlers” hatch a month later, they will situate themselves at the base of a needle and begin to suck the nutrients from the twig. The nymphs feed and grow overwinter while hiding underneath small woolly masses and become adults in early March. They will lay another 10 to 300 eggs that will hatch sometime in April and become adults by June completing two generations within one year. If left unchecked, HWA can suck the needles dry, causing them to fall off. If a Hemlock loses its needles it will eventually die. Some of my fellow Hemlock trees in other parts of our range have died already from only four years of infestation!

As a tree, I can’t check the trees that are standing near me but I can ask you to be on the lookout. All you have to do while you are out and about is gently turn our branches over and look for little white woolly dots as pictured below. Also, I would recommend looking for HWA between the months of November and March, this is the time of year when the adelgids are least likely to be spread. If you find HWA on a Hemlock tree, don’t pull the twig off, just simply GPS the location of the infected tree and get help. Report your findings to the folks at the New York State Department of Environmental Conservation through their website http://www.dec.ny.gov/animals/82617.html or pest hotline listed on their webpage. HWA infestations are treatable through a number of chemical or biological remedies and trees can recover from an infestation.

Hemlock Woolly Adelgid-1311

My friends at the Roger Tory Peterson Institute can give you even more information on HWA and will be hosting an iMapInvasives workshop on May 14 where you can learn even more about effective ways to report invasive species that infect not only Hemlock trees but other species as well. I hope you enjoyed listening to an old tree tell it’s story, and please be looking for HWA this winter as it is a serious threat to all of us.

Elyse Henshaw
Conservation Technician

Photo 1 © Elyse Henshaw; photo 2 © Twan Leenders