Caterpillars spike around lakes and rivers near Aleknagik and Dillingham for second year

Jul 28, 2017

This summer animals gorged themselves on caterpillars while the caterpillars gorged themselves on alder and willow. That resulted in fat gulls, trout and bears and in defoliated vegetation.

Noctuid caterpillars in Wood Tikchik State Park
Credit Daniel Schindler

Visitors to Wood-Tikchick State Park were greeted by an unusual sight this summer. Alders that are normally dense, green and leafy were bare.

“It looks almost like fall came early, so everything’s kind of brown and without any leaves on it,” says Daniel Schindler, a professor from the University of Washington who does aquatic and fisheries science research in the park.

It is the second year in a row that people around Dillingham, Aleknagik, Wood-Tikchik State Park and the Togiak National Wildlife Refuge are reporting a massive outbreak of caterpillars. Schindler is seeing at least two species, one bright green and one brown with dark stripes. They likely belong to the family Noctuidea.

In the state park, the caterpillars’ appetites left their mark along the entire chain of five lakes. Up to the second lake, Schindler says the alders were completely defoliated up to 1000 feet in elevation.

It is the most damage to alders and willows from caterpillars he has seen in roughly 20 years working in the region. As the summer draws to a close, caterpillars are dropping off plants to burrow into the soil where they will winter over in their pupa form. In the spring they will emerge as moths.

Caterpillars ate the leaves off the alders on the bottom slopes at Elbow Point in Wood-Tikchik State Park. This image was taken in 2016. Schindler says this year's defoliation was similar.
Credit Daniel Schindler

Before the caterpillars hunkered down for winter, gulls, fish and bears had a heyday.

“Usually just before the salmon show up, the rainbow trout are pretty skinny, and this year they have big extended bellies on them. When we sample what they’re eating, it’s mostly caterpillars. Even the bears are eating them. The bear scat is full of caterpillar remains,” says Schindler.

Now that the very hungry caterpillars are disappearing, the alders are quickly regrowing their leaves. That’s something Schindler notes that they did last year as well.

“By middle of September when most of the vegetation was starting to go yellow and brown,” he recalls. “The stuff that resprouted was still going gangbusters and was bright green. It’s pretty clear that the plants have some sort of evolutionary history with them. My wonder is whether the plants can handle two, three years of this in a row. That’s where there may be some long term damage to the vegetation.”

Still, it is unlikely that this huge caterpillar population will remain at its current size in the years ahead. Noctuid moths tend to go through a boom-bust cycle.

“In Scandinavia where people have studied them a long time, it’s often a decade between major outbreaks. They’ll explode for a year or two and then disappear for a long time,” says Schindler.

It is unclear when the population will hit its peak and decline, but it does seem that the area will see another spring full of moths.

Contact the author at avery@kdlg.org or 907-842-5281.