Spongy moth caterpillar populations are booming this year. That’s not good for trees.
Ten counties that make up the Chequamegon Nicolet National Forest are under quarantine for spongy moth caterpillars.
Spongy moth caterpillars are about 2.5 inches long with five pairs of blue dots and six pairs of red dots that run down their back in rows.
They’re usually around for about seven weeks before they transform into moths. But during that time, they can do a lot of damage to deciduous trees.
Patrick Engelken is an entomologist in Forest Health and Protection with the U.S. Forest Service based in St. Paul.
He says they start eating leaves almost as soon as trees push them out in the spring.
“Spongy moth caterpillars will eat voraciously at lot of the leaves. During outbreaks, they’ll eat all the leaves off the entire tree. It can be very stressful for the trees. When they eat trees that are already being stressed out like this summer where we’ve had a very dry spring and summer, the trees are already not their healthiest. It just adds another stressor,” said Engelken.
Engelken says a couple of years of that stress can lead to those trees dying.
In Chequamegon-Nicolet National Forest, the Washburn and Lakewood-Laona districts have been hit particularly hard by the caterpillars.
Right now, the insects are at a peak outbreak of their 10-year cycle.
“I know this year we’ve seen a lot of reports of really high populations up in Northern Wisconsin. I was up there doing fieldwork last year. I saw firsthand how devastating it is in some spots,” said Engelken.
Spongy moth populations will eventually crash. The insect is susceptible to some naturally occurring pathogens that grow in moist conditions, but with this dry year that disease can’t keep the population numbers in check.
Landowners can help by killing any of the caterpillars they find.
The Forest Service recommends wearing gloves to collect the caterpillar, pupae, and egg masses you find on your property and drop them in soapy water or a bleach solution.
You shouldn’t touch the caterpillars with your bare hands as the hairs on them can cause skin rash or welts.
Engelken recommends checking wheel wells of cars and campers for egg masses.
“Being really meticulous and searching anything you’re moving from a quarantined county or back into a quarantined county or even if you’re just going out to a campground somewhere spongy moth might occur or other people traveling to from who knows where. It’s a good rule of thumb to search your car, search your camper, search anything you’ve had out on the campground before you take it back with you just to prevent that unnecessary and unwanted spread back home,” said Engelken.
The moth has been found in 20 Eastern and Midwest states.