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The Moths Eating Our Trees

July 22, 2020

By Christie Brodie, Interpretation Projects Coordinator, Royal Botanical Gardens.

If you’ve walked along our trails recently, you may have noticed an abundance of caterpillars and lack-luster foliage in the trees. That’s because this year, Spongy Moth (Lymantria dispar dispar, formerly known as LDD or Gypsy Moths) populations are booming.

Spongy Moths were brought over to Massachusetts in the United States in the late 1860s, with the purpose of breeding them with silkworms to establish a silkworm industry in North America. However, when the moths were accidentally released, they quickly became invasive.

The young, small caterpillars are easily spread through wind gusts. The caterpillars dangle from a thin line of silk and wait for the wind to transport them to another location. While this natural dispersal method is slow, transportation of goods and firewood has expanded their range much faster than what would have occurred naturally.

Spongy Moth Caterpillar
Spongy moth Caterpillar
Moth Adult (Male)
Spongy Moth Adult (Male)
Spongy Moth Adult (Female)
Spongy Moth Adult (Female)

The larvae (caterpillars) of the Spongy Moth feed on the leaves of hundreds of trees and shrubs but tend to prefer Oak Trees. Since Oak Trees are a staple in the Carolinian forest, these non-native pests are threatening this unique ecosystem.

The moth’s population numbers rise and fall cyclically year-to-year. In years, like this one, where the Spongy Moth population is high, it can sound like it’s raining on a bright sunny day in the forest. Not from rain, but from the amount of frass (caterpillar poop) dropping from overhead.

These non-native pests can be frustrating for nature lovers, but there are some ways to attempt to control their population.

On year’s when the Spongy Moth populations are booming, you may have seen trees wearing burlap skirts in our garden areas. The tree skirt (like the one in the photo above) is a simple way to protect leaves from being eaten by hungry caterpillars without harming other creatures. Spongy Moth caterpillars typically feed during the night, and during the day they seek shelter on the ground. When they climb back up the tree to feed, they end up trapped under the skirt. By stopping the Spongy Moths in their caterpillar stage, they can’t breed and contribute to future generations of moths.

Our trees are dressed to impress, and control pest populations!

Tree skirt around trunk of an Oak Tree in Hendrie Park (from 2017)
Tree skirt around trunk of an Oak Tree in Hendrie Park (from 2017)
Spongy caterpillar caught in tree skirt in Hendrie Park (from 2017)
Spongy Moth caterpillar caught in tree skirt in Hendrie Park (from 2017)

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