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Destructive Winter Insects: Bagworms, Mites, and Adelgid

A Bagworm Egg Sac pulled off a Young Spruce Tree.


The bagworm gets its name from the bag that it constructs with silk and pieces of the plant’s foliage. This brilliant adaptation actually allows them to look as though they are part of the tree itself. While the adult bagworm larvae pupate and turn into a moth in fall, female moths then lay up to 1,000 eggs in each bag, which overwinter and hatch the next spring.

While the young larvae of next year are only ¼ inch when they first hatch after they voraciously feed they can grow to be a full inch. Unfortunately, they are often missed until plants begin to brown from the unrepairable damage in late summer.

Spider Mites

This greenish/yellow pest has eight legs and bears resemblance to a spider, hence its name, but is incredibly tiny. In fact, at only 1/64-inch long, you could be standing next to your tree or shrub and not even spot these pesky mites. In fact, you would need a strong magnifying tool to even see them scurry about.

But that’s not to say they won’t do a lot of damage as they feed on its leaves. You can try to scout for mites in your trees and shrubs by holding a white piece of paper under the leaves and gently shaking them. Run your hand across the paper and if there are streaks, you’re crushing and smearing live adults.

Because mites have piercing/sucking mouthparts, when they feed, it creates small, discolored dotting on the leaves. If it is severe, the leaves will look stippled and dull in appearance. In our region, spider mites are hitting boxwoods, burning bushes, spruces, and junipers particularly hard.

Hemlock Woolly Adelgid

These insects feed on Hemlocks. The most distinguishing characteristics of the Hemlock Woolly Adelgid are the white filaments of cotton-like wax produced by the females.

The overwintering females are black and oval and often conceal themselves underneath their characteristic white waxy mass. Severe infestations can lead to premature needle drop, stunted growth, or even the ultimate death of the tree.

Scale Insects

These small, oval insects have a shell-like covering. Some are as large as a ladybug, while others as small as a mark you would make with a sharp pencil. Scale insects damage trees and shrubs by sucking out their fluids. They often go unnoticed until foliage wilts and branches begin to die.

These sneaky pests are good at hiding. At first glance, they simply appear to be bumps on the branches that you may ignore. All the while, they are doing serious damage with their piercing/sucking mouthparts which are used to suck out the tree or shrub’s vital nutrients.

Author: Cindy Giroud

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