23-05-2025
Carlton County is ground zero for spongy moths
May 23—CARLTON COUNTY — As spongy moths, an invasive species that defoliates forests, continue their westward pursuit, Carlton County has become ground zero in Minnesota's effort to scale back the infestation.
Having already infested Lake and Cook counties, the invasive moth, formerly known as gypsy moth, is now gaining a foothold in parts of St. Louis and Carlton counties. To combat this, the Minnesota Department of Agriculture plans roughly half of this year's spongy moth treatments in Carlton County.
"When you look at that kind of population front, it's a lot farther advanced in the north," said Mark Abrahamson, a plant protection specialist with the Minnesota Department of Agriculture.
This summer, the MDA plans to aerially treat 12 different areas within Carlton County, totaling about 27,000 acres, using a pheromone to attract and trap male moths to disrupt their mating.
A spring treatment using Bacillus thuringiensis var. kurstaki — or Btk, a bacterium that kills the moth's caterpillars — also was scheduled for around 800 acres in Carlton County, but that was
canceled after the MDA did not receive the necessary federal funds
for the treatment in time.
The spongy moth is monitored and controlled through a national
Slow the Spread Program
— a partnership between the MDA, U.S. Forest Service and 11 states. In Minnesota, the program has been used to manage 1.1 million acres.
The program estimates it has slowed the spread of spongy moths by more than 60%. Though Abrahamson said there is no way to eradicate the spongy moth, programs like this can significantly slow the spread.
"Without this program, which has been in place for several decades now, it would have been ... pretty much throughout Minnesota, we would just be living with it," Abrahamson said.
Abrahamson said about 75% of the state funding to treat the spongy moth comes from the federal government. Though the MDA is planning its summer treatments, it is a possibility that funding will be pulled again.
"There's always the possibility that something unexpected could occur as well. So we'll be, you know, prepared if that's the case, but we're optimistic that we should be able to move forward," Abrahamson said.
Abrahamson believes the canceled spring treatments won't drastically affect Carlton County's spongy moth population. The moths are already established to a point where Btk would not be as effective as mating disruption, which is more effective among established populations.
"By this summer, we wouldn't expect that people are going to really be noticing a lot," Abrahamson said.
Originally hailing from Europe, the spongy moth first came to North America from Massachusetts in the 1860s as part of a failed science experiment to breed silk-spinning caterpillars, according to Mass Audubon, a New England-based conservation organization. The caterpillars escaped to the scientists' backyard and began their westward conquest from there.
The moth's population has proliferated in the northern parts of the country. Though the reasons are not entirely known, Abrahamson theorizes it could be because the larvae, which move on a silken thread, can travel across lakes great distances.
