Climate change is giving ticks a leg up on their hosts. “It’s about as grody a picture as you can imagine on a dead animal,” a researcher said.
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The biggest number of winter ticks that Peter J. Pekins ever found on a moose was about 100,000. But that moose calf was already dead, most likely the victim of anemia, which develops when that many ticks drain a moose’s blood. So it was probably a lowball estimate, because some of the ticks had already detached.
“It’s about as grody a picture as you can imagine on a dead animal,” said Dr. Pekins, a professor of natural resources and the environment at the University of New Hampshire. (A warning: The pictures below are, indeed, grody.)
Between 2014 and 2016, Dr. Pekins counted ticks on moose calves at two locations in New Hampshire and Maine. He wanted to see how the moose were faring, given that climate change has been delaying snow’s arrival in New England’s winters.
The longer-lasting warmth gives the ticks a leg up as they glom onto the moose, their preferred hosts, in the fall. They then feed through winter and hop off in the spring to lay eggs.
The moose-tracking exploits of Dr. Pekins and his colleagues were published last month in the Canadian Journal of Zoology. They argued that three consecutive years of tick outbreaks “arguably reflects a host-parasite relationship strongly influenced by climate change at the southern fringe of moose habitat.”
While large numbers of ticks, literal bloodsucking parasites, aren’t great for adult moose, they’re especially bad for moose calves, which can die from the onslaught.
With the help of a team that shoots nets from helicopters to catch and tag the calves with radio collars (a process that takes about 15 minutes for the moose and eschews the use of drugs), Dr. Pekins was able to track 179 moose calves. The average number of ticks he found on them was 47,371.
“Anything over 35,000 is trouble for a calf moose,” he said. Over the study period, 125 calves died, 70 percent of those being tracked.
In some ways, the moose are a victim of their own success.
“Maine and New Hampshire had less than 50 moose in the 1970s,” Dr. Pekins said. But their numbers have multiplied many times over since then, thanks to improvements in the available habitat and a lack of predators like wolves.
As a result, Maine now has anywhere from 60,000 to 70,000 moose; New Hampshire had as many as 8,000 or 9,000 in the early 2000s, though the numbers now hover around 5,000. And it’s the abundance of moose that enables the ticks to survive.
“You need a lot of moose on the landscape to have a lot of parasites,” Dr. Pekins said. “That’s the host-parasite relationship.”
That relationship was more or less in balance until the changing climate tilted the scales in the ticks’ favor. Over the long term, Dr. Pekins doesn’t expect the moose to die off completely, but there will be fewer of them.
The ticks don’t want the moose to die off completely, either. “The parasite doesn’t want to kill off its host — that’s bad evolution,” Dr. Pekins said. “Because the parasite loses the game.”
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