Why Are Spongy Moths A Problem?

You've seen spongy moths around, even if you didn't know what they were called, but you probably didn't guess the damage they could cause to your yard.

Spongy moths (formerly called Gypsy moths) are common in Virginia, but they are also an invasive pest. Not only do they damage trees and vegetation, but they can hurt humans as well!

What Do Spongy Moths Look Like?

Why Are Spongy Moths Unwanted Pests?

How Do I Keep Spongy Moths Away?

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What Do Spongy Moths Look Like?

As always, the first step in protecting against a pest is being able to recognize it. When spongy moths hatch, they start out as black and hairy caterpillars. Over time, they turn yellowish-gray with tufts and rows of blue and red spots along their backs, growing to be about 2-2.5 inches long.

After becoming adult moths, the females grow to have a wingspan of around 2.5 inches, while the males stay slightly smaller, measuring under 2 inches. Interestingly, the females do not fly, while the males do.

Spongy moths lay egg masses that can contain anywhere from 500-1,500 eggs. These masses are laid on tree trunks and overwinter to hatch in the spring. Young larvae are buoyant and able to travel up to five miles a day on the wind. The larvae feed heavily on tree leaves, pupating in late summer. Once emerged, the males will travel to find the females, as the females are flightless and have a very small range of travel once reaching adulthood.

Why Are Spongy Moths Unwanted Pests?

Spongy moths were first imported to the United States in an effort to find a silk-producing moth that could be hybridized with silkworm moths. However, during the research period, some of the spongy moths escaped and started defoliating nearby trees. Since that time, spongy moths have been responsible for defoliating millions of acres in the United States (Smithsonian). While the spongy moths prefer oak trees, they will feed on the foliage of most any tree or shrub. By doing this, spongy moths can kill trees directly as the trees can no longer photosynthesize; or, they can kill the trees indirectly by weakening them and making them more likely to die from other wood boring insects or tree diseases.

The destruction can be surprisingly quick. The spongy moth caterpillars feed nocturnally and can eat as much as one square foot of leaves in a day. As many eggs hatch in one area, your trees could appear to be eaten practically overnight. Some larger, healthy trees may be able to survive one or two cycles of spongy moth infestations, but will likely be too weak to survive after that.

Additionally, contact with spongy moth caterpillars or adult moths can leave a person with a rash similar to that of poison ivy. It can appear within minutes or hours after contact and will usually include stinging, pain, welts, bumps or pustules. The symptoms usually dissipate within a few days.

How Do I Keep Spongy Moths Away?

As they say, an ounce of prevention is worth a pound of cure, especially when it comes to pest control. Keep your yard clean and free of dead branches and stumps. Look for egg masses (they look spongy, thus the name) and scrap them off.

The best way to prevent spongy moth infestations is a professionally sprayed pest control application that is suited to spongy moth populations. This is particularly effective if it is in place when the larvae begin to hatch, and regularly applied throughout their life cycles.

If you find moths or caterpillars in your yard, kill them immediately and check daily for additional specimens. There are, unfortunately, no quick fixes for a spongy moth infestation so you'll have to stay on top of it for quite a while.

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For more local Virginia insects and pests, check out our other blog posts and our bug library