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Ticks Love Moose Right To Death — Here's Why

In Explain Maine, an occasional series, we look at some of the things that are unique, interesting and quirky about our great state, and we hope to solve some mysteries as well.

During my first summer in Maine, back in 2014, I covered a press conference in which scientists, tour guides and officials talked about the danger ticks posed to moose and the sadness of being presented with the heartbreaking sight of a moose completely covered in the bloodsucking parasites.

It’s not just upsetting on that level. There are also serious concerns about moose populations dropping over time — and the economic and ecological effects that could have in Maine.

This year, the state issued 22 percent fewer moose permits than it has in the past for the season that ends Nov. 26, with the Department of Inland Fisheries and Wildlife saying it needs to balance the needs of hunters with those of people who want to see moose in the wild.

Clearly this isn’t a situation that’s working out well for anyone — other than moose ticks. One has to wonder, why just moose? Why aren’t deer so badly hurt by ticks?

Evolution is the Answer

As we roll into November here in Maine, moose have finished their mating and are less visible than they were in September and October. But they’re still moving around in the forest, and that means they’re about to start picking up winter ticks.

Starting in November, the six-legged larvae of Dermacentor albipictus — more commonly, winter tick or moose tick — will climb up into trees or shrubs, and when an animal walks by, they’ll attach themselves.

“These ticks climb up a shrub, and they do it en masse, and you probably remember the old game barrel of monkeys, where you pick out a plastic monkey from a barrel and they all come with you?” Maine state moose biologist Lee Kantar says in his stomach-turning description of how that works. “That’s what happens with the winter tick larvae, so the ticks in that clump of ticks, they’re all reaching out with their appendages, and they sense a moose or something come by, and they’re able to grab onto the hair of the moose and all those ticks come with them. So you get a pod of let’s say 1,000 larval ticks, all at once.”

And then they’re on for life. Unlike most ticks, winter ticks live all three of their life stages — larva, nymph and adult — on one host, sucking its blood. A lot of its blood.

And this is where the “but why moose?” question begins to be answered.

Credit University of Minnesota Natural Resources Research Institute via North Country Public Radio
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University of Minnesota Natural Resources Research Institute via North Country Public Radio
Engorged winter ticks. Cringe.

So, Then, Why Moose?

As is so often the case with animal questions, the answer lies with evolution. Kantar says compared to other animals that might make tempting hosts for winter ticks, like deer, moose are relatively recent arrivals in our region, having been in North America for only about 10,000 years

What does that mean? Winter ticks have been living on deer for millions of years, and in that time deer and ticks have developed a sort of balance. Kantar says this likely involves deer becoming aware the tick larvae are there.

If you’re a deer, you’ll likely notice the larvae are there and do something like scraping them off on a tree, or grooming them off with your tongue, before they get to be too much of a problem.

Moose, on the other hand, will go along their merry way unaware of the larvae.

“It doesn’t do anything to defend itself against those larvae once the ticks are on there,” Kantar says, and the ticks live on the moose through the winter, during which time “they take an enormous amount of blood.”

He says by the spring, when the ticks become adults and moose become aware of and irritated by them, “it’s really at a point where they’ve done a lot of damage to that moose.”

Credit University of Minnesota Natural Resources Research Institute via North Country Public Radio
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University of Minnesota Natural Resources Research Institute via North Country Public Radio
Scientists say once infected moose can lose so much blood that they weaken during the winter months.

What Do Ticks Do to Moose?

Well, it’s not pretty. If a tick infestation is bad enough, it can create a situation where a moose dies of acute anemia.

“Essentially so much blood loss in such a short time frame that they can’t replace their blood fast enough,” Kantar says.

This usually happens in smaller animals, mostly, he says, to a calf trying to get through its first winter. That’s the worst-case scenario, but even if a tick infestation doesn’t kill a moose, it can weaken it and make it more vulnerable to disease or predators.

Why is this an increasing problem? Why do we hear so much more about it than we used to? A couple reasons.

First, the one you’d kind of expect: Warmer fall and early temperatures lengthen the season during which tick larvae are actively attaching themselves to moose. The ticks are active when it’s above about 40-50 degrees – temperatures found as late as December.

There’s also another reason: In the 1970s and ’80s, a massive outbreak of spruce budworm that had as one of its results a serious drop in the state’s population of moose.

But the population bounced back, and by the ’90s Kantar says it was at a peak. Which was, as it turns out, pretty bad news for moose.

“Having a lot of moose,” he says, “probably gave a foothold to ticks to increase over time as well, because they have a host that they do well on.”

What’s the Effect on the Population?

Maine and New Hampshire are doing a six-year study on moose mortality, which began in 2014. But early results aren’t fantastic: In 2015, nearly 75 percent of moose calves tagged in New Hampshire died. In Maine, it was 60 percent.

There’s some hope that if the population of moose drops, the population of winter ticks will also drop, and at some point things will level off — some have even suggested that more hunting could help. But Kantar says more warm autumns means more active time for winter ticks, and with those becoming more common, “it’s a tough thing.”

Do you have a burning question about something Maine-y that you’ve been dying to have answered? If so, use this form to ask your question — or email nflaherty@mainepublic.org.

Nora is originally from the Boston area but has lived in Chicago, Michigan, New York City and at the northern tip of New York state. Nora began working in public radio at Michigan Radio in Ann Arbor and has been an on-air host, a reporter, a digital editor, a producer, and, when they let her, played records.