You may not see them, but they’re there. Growing in Lakewood’s tall canopy are tiny invasive organisms that have the potential to wreak havoc on Pacific Northwest forests, especially oak trees.
It’s called a sponge moth.
These tiny caterpillars, with their small yellow heads, furry bodies and distinctive blue-red polka dot patterns, can eat more than 300 species of trees and shrubs and, if left unchecked, can eat all the leaves in a forest from the canopy to the ground within a few months.
Washington State Department of Agriculture staff found five sponge moths in Lakewood in 2025, compared with 10 the year before, so a half-mile area of Lakewood will be treated to eradicate them this April or May, communications consultant Karla Salp said.
This invasive sponge moth caterpillar was discovered in Lakewood in 2024 and 2025 and eradication treatment was carried out in the spring of 2026. Sponge moth caterpillars have a small yellow head, furry body and a unique pattern of blue-red dots.
(Kara Salp/Washington State Department of Agriculture)
It may not seem like much, but the goal is to keep the moths out of Washington for years, Sarp said. Sponge moths are not native to North America and were introduced to the region from Europe and Asia. She said there are more of these animals on the East Coast, but some are making their way to the West Coast on bicycle tires, outdoor lawn furniture or vehicles.
Salp said some people may develop a rash after exposure to caterpillars. In high enough concentrations, spongy moth droppings can cause car crashes because their droppings (which fall from trees) can make roads slippery, she said.
“They have the potential to cause widespread damage,” Sarp said. “If this happens for just one year, most trees – if they don’t have other stressors – can recover and regrow. But when this happens for many years in a row, like in an outbreak, this can actually kill the tree.”
Thankfully, Lakewood is nowhere near those numbers, she said. The goal is to eradicate the moths while their numbers are still low, Sarp said.
Sponge moth caterpillars eat more than 300 species of trees and shrubs and, if left unchecked, can strip a forest of all its leaves from the canopy to the ground in a matter of months.
(Kara Salp/Washington State Department of Agriculture)
Over the next month or two, some residents within a one-mile radius southwest of Custer Road may see a small plane flying overhead, spraying the trees below with a biopesticide called Btk (Bacillus thuringiensis). Btk, a naturally occurring bacterium commonly used for pest control in organic farming, is a safe and effective way to eradicate sponge moths, according to the WSDA.
Btk contains a type of bacteria that caterpillars can’t digest, so when they eat leaves with Btk on them, they die, Salp said. According to the WSDA, numerous studies have shown that Btk poses a very low risk to human health and is not harmful to other insects such as bees or ants in addition to animals, birds or fish.
Salp said not many other moths or butterflies have the same reproductive cycle as sponge moths, which hatch in the spring. She said the WSDA deploys the Btk treatment when about 40 percent of the leaves emerge, which is when sponge moth larvae hatch and caterpillars begin feeding on them. They typically pupate in June or July and emerge as moths in late summer, Sarp said.
The Washington State Department of Agriculture plans to deploy Btk in select areas of Lakewood this spring using a small aircraft. Btk is a naturally occurring bacterium commonly used for pest control in organic farming and is safe for humans and animals.
(Kara Salp/Washington State Department of Agriculture)
“All the damage is caused by caterpillars. Caterpillars eat the leaves and that’s the biggest problem,” Sarp said. “The moths themselves don’t actually eat anything in their adult stages. They basically just mate, then lay eggs and die. That’s basically their life cycle for a year. Then those eggs overwinter, and then the next spring, they hatch out again.”
People can subscribe to alerts about when treatment will occur, which often depends on the weather. If you think you’ve spotted a caterpillar or moth, you can take a photo and send it to WSDA.
“Most people won’t see caterpillars because they’re usually in the canopy,” Sarp said. “Most people don’t see caterpillars unless you see a large number of them climbing up and down the tree, falling out of the tree and then climbing back up the tree.”
