The Scourge Called the Winter Moth

What Is the Winter Moth?

The winter moth is an insect whose offspring feed on the leaves and flower buds of trees and flowering plants. They come from Europe originally and are considered an invasive species in North America. Winter moths number in the millions and create a tremendous amount of damage to trees like maple, white elm, cherries, ash, basswood and several others.

Identifying Characteristics of Winter Moths

Female winter moths are small, only about 8 mm in length. They are gray in color, have no wings and are unable to fly. The males are larger than the females and may be light brown or tan in color. The trailing edge of the moth’s wings have a fringed appearance.

Life Cycle of the Winter Moth

Adult winter moths emerge around Thanksgiving, coming up from the ground in late November and into December. After the adult moths emerge, the female, who cannot fly, climbs to the base of a tree and then goes about attracting a mate by producing pheromones.

After the moths have mated a female will lay approximately 150 eggs in crevices in the tree or in the tree bark. Both the males and the females die shortly after mating.

When springtime comes, the eggs hatch into inchworms. The inchworm’s are smooth and green in color with a thin white stripe running lengthwise down either side of their body. The caterpillars make their way to the tops of the trees by spinning a thin strand of silk which allows them to ride up air currents to the treetops.

It is here that the damage to the trees begins. The caterpillars will feed on leaves and flowering buds, devouring everything they can from March or April until mid June when they make their way down to the soil to begin the transition from caterpillar to moth.

The Damage They Can Cause

Shortly after hatching, the winter moth larvae burrow into the flower buds and begin feeding. When one flower bud is completely devoured, they will move on and begin feeding on another. The older larva feed on the leaves and foliage of trees.

The larvae of the winter moth are voracious eaters and the defoliation they cause can result in the death of the branch that the leaves are on, or even the death of the entire tree.

What Can Be Done to Stop the Winter Moth

One popular method for dealing with winter moths is a technique known as tree banding. This is done by putting a paper or plastic strip around the tree. The strip is covered in a sticky substance and the idea is that as the caterpillars are making their way up the tree, they will get stuck on the tree band and die.

The problem is that this particular method is not very effective. Some caterpillars can make their way across the tree band and some can find a way under it.

There are also oil sprays available that can be applied to tree trunks and branches. The oil is supposed to kill the eggs before they can hatch, but this method does not yield perfect results either.

Another method for dealing with winter moths is to use Bacillus thuringiensis (kurstaki), or B.t.k. for short. This is a bacteria that, when ingested by a caterpillar, will become active and begin to multiply. When the bacteria multiplies they produce toxins which are lethal to the caterpillar. This technique works well with younger caterpillars, but the older ones are not as susceptible.

There is an insecticide that can be used to deal with moths that is also based on a bacterium. Insecticides known as Spinosad products work effectively on all ages of caterpillars, affecting their nervous systems. These pesticides are not harmful to parasites and predators, but they can be harmful to honey bees.

In addition to the various methods mentioned above there are also certain insecticides that are only available to licensed commercial applicators and not available for homeowners to purchase. One such product is known as Tebufenozide. This product works by mimicking the molting hormone in caterpillars, preventing them from molting or shedding their exoskeleton. When they cannot grow and form a new exoskeleton they will die.