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By: Robin Ford Wallace, Reporter


Hemlock woolly adelgids don’t zoom into a hemlock forest like an invading air force and commence Bliztkrieg. Rather, the barely visible insects sneak in, cadging a ride on bird feathers, animal fur or even a hiker’s flannel shirt, says Donna Shearer of Save Georgia’s Hemlocks.

“They land on the tree by hitchhiking to it, and then the adult will lay an egg on the tree right at the base of the needle. It’s a little cottony-looking thing, what looks like a tiny, tiny cotton ball, and inside the egg sac, the little cotton ball, could be anywhere from 30 to 300 babies,” said Ms. Shearer. 

“They hatch in the early spring and migrate down the branch and find themselves a nice hemlock needle, and they set up camp there and sink their feeding tube, called a stylette, down into the base of the needle, where the needle joins the branch, and they suck out the starches and nutrients from that needle and it dessicates, it dries up, and eventually will fall off. So when the needles fall off the tree, the tree can no longer do photosynthesis. That is the process by which the tree makes its own food, so the tree actually dies by starving to death.”

Two generations of adelgids are born each year. So if there are 300 larvae, or “crawlers,” the first generation, the second generation can reach 90,000, said Ms. Shearer. “You could go from one egg sac to 90,000 bugs in one year, and then those are going to lay eggs and go through two more generation, and by the end of the second year you could have 80 billion insects from that one egg sac,” she said. “They can quickly overwhelm even a large tree.”

The cottony egg sacs at the base of hemlock needles are the most visible sign of adelgid presence. As the infestation progresses, the tree’s color fades from a bright emerald green to a duller gray-green. The tree can still be saved at this point, but action is not taken the tree will die – and so will those surrounding it.

And when acres of hemlocks die, it’s not just the trees that are lost, said Ms. Shearer. “The result is that it completely changes the natural environment,” she said. “When the trees die, the water dies. You get soil erosion, runoff into streams. It opens up the canopy so that invasive species can come into the forest. It changes the habitat in terms of shade-loving plants, many of which depend on hemlock habitat.”

Animals in the area also suffer, said Ms. Shearer. “There are several species of migratory birds, for example, that depend heavily on hemlock habitat, and we don’t know what will happen to the animals that are associated with hemlock habitat, whether they will go elsewhere or choose other trees or suffer in some other kind of way,” she said. 

“The trout industry is also likely to suffer because the hemlocks that grow along the trout streams keep the streams cool with their shade and the trout do need cold water, and their root systems keep the stream clean and clear, and trout need that for laying their eggs.”




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