The small, brown moths clinging to trees in North Cheyenne Cañon Park are on the cusp of death, but eggs left in their wake could endanger forests across the Pikes Peak region.
Parts of this popular Colorado Springs park were hit in the summer pf 2015 by two species of defoliating moths – part of a simultaneous outbreak that stripped the needles from thousands of otherwise healthy Douglas fir and white fir trees.
City and state foresters scrambled to prevent a repeat performance in 2016, warning it could have dire consequences.
“If we have repeated defoliations, these trees will die,” said Dennis Will, staff forester for Colorado Springs Parks, Recreation and Cultural Services. “Depending on how large this thing gets, we could be talking about thousands of acres of dead trees.”
The moths began to feed in late May and early June of 2015, nourished by lush growth after the wettest spring on record in El Paso County.
Will estimates the infestations damaged 2,000 acres on city-owned property, including Bear Creek Canyon and Blodgett Peak Open Space, and moths can be found in pockets scattered across Pike National Forest northwest of Colorado Springs.
In the Pikes Peak region, the problem is most pronounced in North Cheyenne Cañon Park, where visitors have responded in shock to orange and brown trees, some gone bald at the crown. Though many hikers suspect pine beetles – a more familiar scourge – it’s moths in their larval form that are to blame.
“We get most of our complaints on Mount Cutler Trail, which is one of our most popular trails,” said Bob Falcone, president of Friends of Cheyenne Cañon, who described one variety of moth caterpillars as “fuzzy little things” that swarmed on tree boughs before transforming into moths.
One of the invaders, the tussock moth, hatched in numbers not seen in a couple of decades. Then, they were a significant problem in the Rampart Range, where an outbreak killed thousands of trees over a two- to three-year stretch before the tussock moths died off naturally.
This year, they appear to be a waning threat after only one season, their ranks thinned by nuclear polyhedrosis virus, which caused mass die-offs and is likely to prevent the tussock moths from returning in substantial numbers in 2016.
But the virus has no effect on the second species of invader, the western spruce budworm, raising concerns that by spring of 2016, the millions of eggs they left in their wake could come roaring back to life, further damaging forests already weakened by a season of defoliation.
What caused the problem is unclear. Outbreaks of tussock moths and western spruce budworms tend to recur in cycles, said Dave Leatherman of Fort Collins, former entomologist for the Colorado State Forest Service. Colorado Springs appears to be one of the few areas where they regularly appear in tandem, even competing for food on the same trees, Leatherman said.
“You have two fairly voracious defoliators occurring simultaneously in space and time, and you don’t normally see that in forestry,” Leatherman said. “Usually it’s one thing at a time.”
The prospect of large die-offs of Douglas fir and vulnerable white fir populations is more than an aesthetic concern.
If the trees die, they will raise the fire threat along the Front Range by providing thousands of acres of fuel. Large swaths of dead trees also can worsen runoff, a particular concern along Bear Creek, which contains the last known population of genetically pure greenback cutthroat trout.
To combat the problem, city parks staff convened a meeting with the Colorado State Forest Service and several other entities battling the moth infestation, including Colorado Springs Utilities, The Broadmoor hotel, El Paso County parks and the U.S. Forest Service.
One proposal suggests calling in a helicopter or single-engine air tanker in June 2016 to dive bomb swarming larvae with BT, or bacillus thuringiensis, a naturally occurring soil bacterium that kills moths and butterflies but leaves other species unharmed.
It’s an expensive fix. Perry Park, in Douglas County north of Palmer Lake, recently sprayed for tussock moths at the expense of $63 per acre.
For Colorado Springs alone, the tab of an aerial assault could reach $150,000, Will said.
“This is the biggest project that city forestry has ever had,” he said. “We’ve got lots of homework to do. We’re learning as we go.”
One task remaining is to determine the extent of the infestations, which is being done with the help of aerial surveys by Colorado State Forest Service and the U.S. Forest Service, the city said in a news release.
Even as the city prepares for an outbreak, it’s possible the problem could end naturally. In the past, similar bug problems have been eliminated by checks and balances inherent in Mother Nature, Leatherman said.
In the case of western spruce budworm, spiders, predatory insects and birds can help keep populations in check, as can spring freezes and changing weather. Whether natural solutions come into play is yet another unknown, Leatherman said.
“One of the biggest friends these insects ever had was Smokey the Bear,” Leatherman said. “When he took fire out of the system, that created some imbalances in the trees that insects are left to rectify.”
“I always say, ‘Fire, beetles or log trucks – pick one.'”
What We Believe
We are driven by our deep respect for our environment, and our passionate commitment to sustainable tourism and conservation. We believe in the right for everyone - from all backgrounds and cultures - to enjoy our natural world, and we believe that we must all do so responsibly. Learn More