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In the last half of June, visitors to the Potter Park Zoo and passersby on the Lansing River Trail got an eerie feeling near the parking lot pay booth. The expansive parkland north of the booth somehow feels wrong, but it takes a few seconds to realize what is happening.
The wooded area north of the parking lot and west of the picnic pavilions — a large thicket covered by 100 or more oaks, maples and other towering old trees — was almost completely stripped of its leaves by last week.
Gypsy moths, one of the most destructive pests in North America, have taken over.
Richard Kobe, chairman of the MSU Forestry Department, recently biked past the affected area.
“It’s quite striking,” Kobe said. “The defoliation makes it look like early spring.”
Some nights, as dusk falls, you can stand under the trees and clearly hear the moth’s spiky larvae, or caterpillars, crunch away. It sounds, and feels, like a soft rain as they munch the leaves. Fine leaf debris, as if from a mulching mower, blankets the hillside.
Lansing Parks Director Brett Kaschinske said the city is monitoring the attack. Most of the damage is already done, he said, because the caterpillars will turn into moths in July.
Gypsy moth hatches are “eruptive,” varying drastically from one egg for every 2.5 acres to 1,000 for every 2.5 acres, according to the U.S. Forest Service. When an unusually wet spring comes after two successive dry springs, as happened this year, conditions are right for an “eruption.”
Kaschinske said the Potter Park trees will survive the onslaught, bad as it looks now. Kobe agreed.
“We probably won’t see major long-lasting effects,” Kobe said.
Hardwood trees produce a second set of leaf buds, in late July or early August. That should give the trees enough solar panels to keep them alive during the winter.
It takes several successive years of moth hell to kill a tree, and even then, only about 20 percent of affected trees die, although large-scale die-offs happen.
Kobe said the usual annual die-off, about 1 percent, might increase to 2 percent.
The city has no plans to wage chemical warfare against the moths. Kaschinske said there are already signs of naturally occurring viruses and fungi that will “keep these things in control.”
“Unfortunately, the population of moths has to hit a high before that starts to take over,” Kaschinske said.
When the population peaks, the moths start stressing each other, instead of the trees, leaving an opening for a virus disease called NPV to decimate the population. High gypsy moth populations collapse in three years or fewer, according to the MSU Extension Service.
Like them or not, gypsy moths have become part of the ecosystem of North American forests since they jumped the Atlantic 150 years ago.
“Last year, extensive areas of northeast lower Michigan got hit by gypsy moth,” Kobe said.
Unlikely as is seems, scientists know exactly whom to blame for all this. A portrait painter and amateur entomologist named E. Leopold Trouvelot brought gypsy moth egg masses to Boston from his native France, started raising them in his backyard in the 1860s and accidentally allowed some of them to escape.
By the 1880s, the buggers were defoliating trees in Boston and quickly spread through North American hardwood forests. They are a hardy and determined lot, as recent visitors to Potter Park will attest. After trying burning egg masses and using pesticides, foresters all but gave up on fighting them over 100 years ago.
“After this accident, Trouvelot apparently lost interest in entomology and became interested in astronomy,” reads a deadpan entry in the U.S. Forest Service website.