Experts see few other ways to stem the grisly pests
By Will Thorn
Too many moose are ambling the regenerating forests of Essex County, the corner of the Northeast Kingdom where the elusive, droopy-faced creatures tend to congregate in Vermont. At least, that is, according to the state.
Vermont’s fish and wildlife board voted in April to issue 180 moose hunting permits for this year’s season, administered exclusively in Essex County. The allotment is expected to cull about 10% of the population there and bring density closer to one moose per square mile — a move to stem the species’ primary antagonizer, the winter tick.
Most probably prefer a strategy that doesn’t involve hunting an iconic species on the decline, and animal activists say permits embolden hunters to go after trophy bulls, not suffering, tick-ridden moose. “Having a season on moose already suffering from serious threats sounds irresponsible,” said Brenna Galdenzi, president of the Stowe group Protect Our Wildlife.
Experts have probed other ways of defeating the ticks — fungal pathogens and pesticides, genetic engineering, more habitat — but those solutions are still being studied or only stopgaps. As unpalatable as culling moose seems, it may be the only way to prevent more of them from being bloodied, emaciated, freezing and dead.
“People hear, ‘Oh, moose are dying from winter ticks,’ but they don’t really grasp what we mean when we say a load of winter ticks; they think we mean a couple thousand,” said Josh Blouin, a wildlife specialist with the Vermont Department of Fish and Wildlife. “So when you tell people we’ve counted 35,000 winter ticks on half a moose calf, you can see their eyes widen, and it takes their brain a minute to really comprehend what that even means, what that even looks like.”
Blouin worked on a research team that tracked 90 calves under a year old fitted with radio collars between 2017 and 2019. In two of the three years, winter tick outbreaks killed more than 50% of the calves. On average only 49% of them survived their first winter to their first birthday.
“The public I think oftentimes sees the moose as this declining species facing all these problems, and the management solution is to kill more of them. Like, is that the right thing to do?” said University of Vermont professor Jed Murdoch, who worked with Blouin on the study, published in 2021. “But at the same time, if you see these moose in the environment, and you see what sort of poor state and poor health they’re in … you can’t help but say, ‘We’ve got to try to do something to make healthier moose here, and what can we do?’”
Other animals, like white-tailed deer, carry winter ticks. But moose never developed the same attention to good grooming as those species. When they start feeling the ticks, it’s long after the pests have accumulated and started gorging. Clumsily they try rubbing the ticks off on trees, tearing off patches of their protective, insulating hides.
The sheer number of ticks on a given moose makes grooming a futile endeavor regardless, even if the beast could pluck them off with tweezers. Winter ticks are “almost like a whole layer of skin underneath their guard hairs,” Murdoch said. Infestations get so bad that “there’ll be a blood stain in the snow because they’re popping all those ticks from their weight.”
When Murdoch and Co. were tracking moose, they’d go into the field to perform necropsies when one of the collared animals died. Coming across an intact carcass of an infected calf, they’d remove its hide and halve it before trimming away hairs and counting ticks by hand, shuffling between 10 by 10 centimeter patches in a grid. The highest number of winter ticks on half a calf hide Blouin said he could recall was about 35,000.
“Probably conservatively, you could say there were 70,000 or more winter ticks on some individuals, likely more on others,” he said.
Moose breeding season coincides with winter ticks’ questing period, a time when thousands of larvae climb up to the edge of vegetation and wait for an unsuspecting host to brush by, said Nick Fortin, deer and moose project leader for the fish and wildlife department and member of the 2021 study.
The combined factors of increased moose movement during breeding and a high density in the Essex County area increase the chances a moose will pick up and spread winter ticks.
Shortening winters have also improved the chances of ticks surviving and reproducing. The longer warmer weather persists in the fall, Fortin said, the more chances larvae have to latch onto a moose before colder weather or snow sends them to an early grave. In the spring, a female tick diving onto a forest floor covered with leaf litter instead of snow is far more likely to both survive and lay the eggs of ticks that will harass moose in the fall.
It’s a conundrum with many variables and few easy answers. As Murdoch put it, “What other tools do we have in our toolkit?”
Well, here’s one: biopesticides, or natural substances or species that can combat pests.
UVM professor Cheryl Sullivan, an insect expert, said there is a rising demand for alternatives to traditional but harmful chemical pesticides. She has studied how to manage pests like winter ticks via fungal pathogens, for example.
Outside rare instances of “biological warfare” between the pesticide and its host, ticks don’t develop resistance to biopesticides like they do to chemical ones, Sullivan said. But she said biopesticides would be difficult to use for winter ticks because of their wide dispersal across the state and their location is uncertain.
“In order to get funding to look at this specific problem, it would be extraordinarily expensive, and it would take many years of research to show that it’s efficacious, especially in the wild,” she said.
Likewise, treating the entire 650 or so miles of the Essex County wildlife units isn’t going to happen “unless someone wants to give us several billion dollars,” Fortin said, though he added the strategy might work on a smaller scale if unintended consequences prove manageable.
What about treating the moose with chemical pesticides as a preemptive measure, much like a person putting on bug spray?
The ticks would likely develop a resistance to them, Sullivan said, and it would be difficult to get moose to eat enough treated food to get an effective dose.
Murdoch mentioned fighting winter ticks with a gene drive, the genetic modification of a species to drive a change through its population. He cited the federal government’s approval of gene drives to kill disease-carrying mosquitoes by releasing genetically engineered males who would pass on a gene lethal to female offspring.
Murdoch doesn’t believe this idea is being discussed. Gene drives typically happen with non-native species and for the benefit of humans, not other animals, he said, and could come with an unappetizing price tag.
Moose like to live in regenerating forests, and experts have thought about creating such landscapes to spread out the animals’ population. But “just because a landowner in central Vermont creates young forest, it doesn’t mean all of the sudden moose are gonna come flocking there. It’s got to be where moose already exist and where they’re thriving,” said Blouin.
All told, said Murdoch, “the most practical, cost-efficient and quickest way of dealing with the problem is probably reducing moose density.”
That doesn’t mean, however, that the department’s approach hasn’t been met with criticism. Galdenzi, from Protect Our Wildlife, said that “the moose herd is suffering from so many stressors that we think they should be protected at this point and not hunted.”
She believes a moose-hunting season is a “complete abdication of responsibility to these animals” that only incentives trophy hunting.
Galdenzi said the weather and winter severity were bigger indicators than moose density of the number of winter ticks on a moose and questioned whether the 2021 study existed to maintain the moose season.
Rick Joyal has a different approach. Joyal, a lifelong hunter and director of the Derby Fish and Game Club, said he was “almost 100% sure” the roughly 500 members active in the club per year would support hunting as a way for fewer moose to die from winter ticks.
“My opinion is that more moose were killed because of ticks than were taken by rifles or by hunting, and I think that when they say to keep the population in the carrying capacity of the land, I think that’s the way to go,” he said.
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