How Do You Kill an Invasive Species? Bring In a Bigger, Meaner Species to Eat It (The Walrus)
In Southwestern Nova Scotia, one morning in late July, forester Mary Jane Rodger picked up a hemlock branch clipped from the towering canopy overhead and leaned in close to examine a fleck of white on its delicate dark-green needles. She was on the lookout for signs of a killer—one that now puts all of the province’s hemlocks at risk.
Eastern hemlocks, with their narrow trunks and scaly bark, don’t have the obvious majesty of Western red cedars, but stands like this one create their own magic: a permanent cool twilight, a moss-carpeted microclimate that shelters everything from migrating birds to brook trout. In Nova Scotia, where much of the province has been logged since the arrival of Europeans, long-lived hemlocks make up a significant part of the sliver of old-growth forest that remains, spared by their low commercial value and ability to grow in hard-to-reach areas like the banks of rivers. Yet, having made it to the twenty-first century, these survivors are now threatened by a tiny menace lurking on their branches.
In search of this threat, Rodger held the branch close to her face. “It’s just sap,” she concluded after a moment’s inspection. Rodger was looking for the egg sacs of a tiny sap-sucking insect known as the hemlock woolly adelgid. The sacs, which are the most visible sign of the adelgid’s presence, look like many things: cotton wool, spider eggs, bird poop. “It’s this weird dichotomy because it’s like a treasure hunt,” Rodger says—except, in this case, “you don’t really want to find what you’re looking for.”