Caterpillar peak may have passed
Forest tent caterpillar numbers crashed in 2014, a year they should have multiplied, surprising forest pest experts but leaving residents and visitors of northern forests grateful and their trees intact.
Even better news is that the number of leaf-eating north woods caterpillars likely will be down again this year just when it was expected they would peak.
That was good for anyone planning outdoor reunions, weddings and camping trips in May and early June when billions of the caterpillars were expected to be writhing around the region.
"My prediction for this year is that most people and most places will not be seeing FTC," said Mike Albers, Grand Rapids-based forest health specialist for the Minnesota Department of Natural Resources and one of the state's leading authorities on the pest. "My guess right now is that it will be similar to last year."
Albers was out in the woods in April looking for forest tent caterpillar egg masses in the crooks of trees, mostly aspens. Those caterpillars — sometimes incorrectly called "army worms" — usually crawl out in early May..
Forest tent caterpillars last peaked in 2001 and 2002 when they defoliated more than 7.3 million acres of forest each year, the largest outbreaks in recorded history. They rendered trees bare, ruined orchards and wiggled up the sides of homes and across roads and driveways, eating and defecating before they wrapped themselves in cocoons to metamorphose into little brown moths that lay eggs and start the cycle again.
As expected, the caterpillar numbers eventually crashed after they overpopulated, eating themselves out of food and starving. They also succumbed to disease, especially a parasitic fly that emerges on the heels of every forest tent caterpillar outbreak.
By 2006, only 1,900 acres were defoliated statewide, the low point of the most recent cycle.
Then slowly, as they have every decade since people paid attention, the native caterpillars began to expand in number and range across northern Minnesota. By 2012, they defoliated 274,000 acres and in 2013 that number skyrocketed to 1.1 million acres.
By then, because large-scale outbreaks have occurred every 10 to 15 years over the past century, Albers and other experts assumed that the next peak caterpillar outbreak was near, likely between 2014 and 2016.
But then something happened to reverse the caterpillars' course. Last spring, very few if any caterpillars emerged from their egg masses to munch aspen leaves, their favorite food.
Albers has a theory why forest tent caterpillars never reached their expected peak and appear to be declining. Those parasitic flies — often called friendly flies because they like to land on people, but can't bite people — increased far sooner than usual during an FTC cycle.