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The Impact – Forest-wrecking Spongy Moth Caterpillars and Other Invasive Species

Mike McClanahan profile by Mike McClanahan

The Washington State Department of Agriculture is focused on eliminating as many spongy moth caterpillars as possible in parts of two counties.

 Native to Europe and parts of Asia, the spongy moth has been in North America for more than a century now. The destructive capabilities of spongy moth caterpillars have earned the species a special place on the least wanted list.

 They prefer deciduous trees, oaks are their favorites, but in large enough numbers will also strip evergreen trees of their needles. 

 In the Northeast, spongy moth outbreaks are blamed for defoliating entire forests, destroying hundreds of thousands of acres of hardwoods in states like Connecticut and Massachusetts. 

 The damage in Rhode Island was so extensive between 2015 and 2016 that it was picked up by satellite images.

 The state department of agriculture has been waging a war of attrition against the spongy moth since 1974 using a network of traps to figure out which areas are prone to an outbreak when the weather turns warm.

 They caught more moths in the Steamboat Island area of Thurston County than anywhere else. According to WSDA, it was the highest concentration of moths in thirty years. Aerial spraying to kill the caterpillars began May tenth, focusing on about 1400 acres of steamboat island and Hwy 101.

 The agency is also planning to spray 900 acres near the community of Concrete in Skagit County,

 This week we spoke with Sven Spichiger, Pest Program Manager with the Plant Protection Division of WSDA.

 “A defoliation event is pretty tough to live through. I grew up in the East, so I’ve been through a number of them. And what I can tell you is a defoliation event is when the population of caterpillars gets so out of control that they literally strip every leaf, every blade of grass, everything but an occasional lonely mountain ash tree, which is one tree they won’t eat,” said Spichiger.

Raising awareness of the many potential points of entry for the dozens of destructive species that could wreak havoc here is the job of the Washington Invasive Species Council.

We sat down with the council’s Executive Coordinator Stephanie Helms. For an overview of high priority invasive species besides the spongy moth, from razor-sharp, rapid spreading shellfish to dangerous plants like Giant Hogweed.

 “That sap gets on their skin and that skin is then in the sunlight, it can actually result in third degree burns,” said Helms.