Land Matters: Invasion of the Hemlock Wooly Adelgid

April 10, 2017Rebecca

Invasion of the Hemlock Woolly Adelgid

If you have ever walked in a hemlock forest, or fished a stream in a hemlock ravine, you know that these are magnificent trees. Growing tall and stately, this evergreen species creates a shady forest canopy that can feel absolutely magical. They are an important and much loved constituent of our Columbia County forests. Today, thanks to a tiny little insect that traveled here all the way from Asia, they are in grave danger.

On Thursday April 20, the Columbia Land Conservancy, together with Cornell Cooperative Extension and a number of other organizations, is co-sponsoring a workshop at Columbia Greene Community College to provide information about this urgent threat and what might be done to head it off, or at least to lessen the potentially devastating impact.  People who own or manage forest land, farmers, hunters and fishermen, natural resource educators – and anyone who shares an interest in the natural world or concern about invasive species – are encouraged to attend.

Why Should We Care About Hemlock Trees?

The hemlocks found in Columbia County are called Eastern Hemlocks. They are one of ten hemlock species found throughout the world. Hemlocks are widely valued for their gracefulness and beauty. They are the only conifers found in many low-lying deciduous forests, and in those areas provide unique year-round shade. They are found not only in extensive natural forest stands but are used widely as ornamental plantings. However, they are not just another pretty tree. They are a species of particular importance to the ecosystem – a so-called “foundation species.”

Foundation species are tree species that define the forest structure and control ecosystem dynamics. We humans depend upon the ecosystems that they build and maintain for a wide range of tangible and intangible services. Hemlocks commonly grow along headwater streams. They moderate water temperatures that allow trout and other species to thrive.  Indeed, hemlocks have such a distinct influence that streams flowing through hemlock forests support unique assemblages of salamanders, fish, and freshwater invertebrates.  Hemlocks help to maintain good water quality by providing a buffer for nutrient inputs.  They stabilize shallow soils, especially on the banks of steep gorges where they are often found. They provide critically important habitat for a number of animals, particularly in winter. Several wildlife species are dependent upon the environment that exists in hemlock stands. And some species specifically depend on the presence of hemlocks for their very survival. Without hemlock trees, entire ecosystems that play an important role in the natural world and on which we rely will disappear.

So What Is Happening?

About 60 years ago, a tiny insect from Asia found its way to the mid-Atlantic United States. It’s called a hemlock woolly adelgid. Over the years, this little creature, which lives off the sap of hemlock trees, has thrived in its new home and has been expanding its territory, steadily creeping northward.  It has now reached us here in Columbia County, in the Catskills and the Finger lakes.  It hasn’t yet made it to the Adirondacks.

This is a story repeated a thousand times over. With the vast increase in international shipping and commerce, species that have lived in harmony with their native environments for ages are transported to faraway places where they wreak havoc on their new surroundings. The hemlock woolly adelgid feeds off the hemlock species that exist in Asia, but those trees have developed a resistance mechanism that, together with certain natural predators, allows the trees to survive. Here in the Eastern United States, the insects go after their usual food source, and lacking both natural resistance and natural predators the impact on the trees is devastating.

These little insects can be a difficult to see. Hemlocks are evergreen trees with short, flat needles that extend on either side of the branches. If you examine the underside of a hemlock branch that is infested, you will see tiny white “woolly” balls of fuzz at the base of the twigs that resemble cotton balls. These appear in the winter when the females lay their eggs, but typically persist for a long time. The insects feed on the sap of the tree by inserting a long sucking tube, ultimately causing the tree to become diseased and die, a process that can take from 4 to 15 years. Vast stands of hemlock in the Smokey Mountains and other regions to the south have by now disappeared entirely, with barren skeletons of standing dead tree trunks bearing witness to the devastation.

What Can We Do About It?

The challenge posed by the hemlock woolly adelgid is daunting, to be sure. But unlike the threat from similar invasives, such as the emerald ash borer, whose impact is widely accepted to mean the inevitable disappearance of the ash tree, it may yet be possible to staunch the damage and save the Eastern Hemlock and, with it, the important and complex ecosystems that depend upon it.

The Department of Environmental Conservation is doing a lot of work to study possible solutions. It is using certain pesticides that are directly injected into each individual tree or applied to its bark. These have been found to successfully stave off hemlock woolly adelgid infestation for as long as seven years. Over the long term, there is hope that another little insect, the Laricobius nigrinus (or “Little Larry”) may serve as an effective control. Little Larry is native both in Asia and in the Pacific Northwest, and in both places serves an important role in limiting the impact of the hemlock woolly adelgid. But extensive research is necessary before releasing this new species into our forests to ensure that it won’t in turn bring about some other monumental threat to our ecosystem. Such research is actively underway.

The challenge posed by the hemlock woolly adelgid is complex and multi-faceted. The threat is very real. The loss of this species would have a devastating impact on our forests and the broader ecosystem. It isn’t yet clear how it is all going to turn out.

Certainly, anyone who owns or manages land with hemlock on it should be aware of the issue, should be checking for signs of the presence of the hemlock woolly adelgid and should be prepared to respond promptly upon seeing it. Early detection is essential if there is to be any chance of achieving control.

If you would like to find out more about this complex challenge and about steps you can take to combat it, plan to attend the workshop at Columbia Greene Community College on Thursday April 20, from 2:00 p.m. – 4:30 p.m. For further information about the program contact; or call 518.622.9820, ext. 0.  The program is without charge, but registration is requested at:

PDF pagePrint page