Invasive Species Alert: Hemlock Woolly Adelgid 

As you venture around the trails this winter, keep an eye out for this special tree in particular – the Eastern Hemlock (Tsuga canadensis). The Eastern Hemlock is New York’s preferred conifer, with more Tsuga canadensis species found in New York than in any other state in the nation. Vastly concentrated in the Adirondacks, the Eastern Hemlock is integral to New York’s forests, character, and heritage.

Under its branches lies a whole host of benefits to our New York State forests and streams. The tree’s dense canopy provides shelter to animals through harsh winters and keeps forest floor and streams cool during summer, enhancing oxygen-rich stream conditions for trout and other aquatic species. Hemlocks on streamside banks also help to control erosion and filter runoff from human sources. This beneficial ecosystem is now under threat. Entire forests of Eastern Hemlock are being devasted by rising temperatures due to climate change and the spread of the invasive insect, the hemlock woolly adelgid.

Tiny Pest, Huge Threat

Secretions of the hemlock wooly adelgid. Photo courtesy of NYS Hemlock Initiative.

The hemlock woolly adelgid (or HWA) is a non-native invasive forest pest that originated in Japan. Without natural predators, it has flourished in the eastern seaboard of the United States and southeastern New York over the last half-century. This small, aphid-like insect is easily spotted in fall, winter, and spring by the white, woolly masses they make near the base of needles on the tree’s stem. As described by the New York State Hemlock Initiative, “the wool is secreted by the insect, acting as a natural buffer from wind and cold and serving as an ovisac for laying eggs.”

As HWA creeps north, the effect on its host tree is notable. Over a period of several seasons, the HWA uses its straw-like mouthparts to feed on the tree’s twigs. At each of these punctures, the tree isolates that wound or section by using chemicals to prevent the flow of nutrients and water. As an increasing number of the tree’s stems become isolated, the transport of food and water is blocked and new tree growth is prevented. The tree eventually succumbs to the infestation.

Citizen Science Initiative- You Can Help!

With no natural predators and research into biological controls still ongoing, whole forests of hemlock from North Carolina to Long Island have been stripped of the Eastern Hemlock. The biggest step to helping the Eastern Hemlock and New York’s forests is to identify the location of the hemlocks and monitor for HWA infestations. Thanks to the New York State Hemlock Initiative (NYSHI) and the Capital Region Partnership for Regional Invasive Species Management (PRISM), there are a variety of mapping and reporting efforts on this invasive species. The Mohawk corridor is currently considered to be one of the last lines of defense HWA has yet to cross – getting familiar with the NYSHI and PRISM resources and monitoring MHLC Preserves and Capital Region lands for this pest is a great way to help!

In the new year, as we work towards the improvement of ourselves, our region, and our planet, the first thing to do is take a step! I encourage you to go outside this winter, be curious, and care about the natural world here along the Mohawk and Hudson Rivers! We are looking to continue our training and implementation of invasive species monitoring and controls on our preserves – please feel free to email me with any trail, land, or invasive species comments or concerns at

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