Threat of moose-killing tick infestation looms as far-north climate warms
Yareth Rosen
A small but dangerous parasite, the winter tick,
is spreading north and west as winters become
shorter and now is knocking at Alaska's border.
A researcher holds a tick plucked off a dead moose in
Minnesota. (Ron Moen / University of Minnesota Duluth)
populations in New England and the upper Midwest,
has been confirmed in Canada's Yukon Territory and
in the Northwest Territories, where it's infecting elk,
mule deer and some moose.
"Now that they're moving farther north through
Canada, north and west, they're eventually going
to arrive here, if they're not here already," said
Kimberlee Beckmen, wildlife veterinarian for
the Alaska Department of Fish and Game.
"We will be next. It's only a matter of time."
For moose, the winter ticks' effects can be
gruesome. The ticks gather in the fall on
forest plants, latch onto passing animals
and stay there through the winter, swelling
to the size of grapes as they feed off their
hosts' blood.
Tens of thousands of ticks can latch on to a
single moose. They make the moose itchy,
uncomfortable and prone to spending a lot
of time and energy scratching, sometimes
rubbing away fur, and too little time eating.
"It makes them waste away and eventually
freeze and starve to death," Beckmen said.
"It's pretty horribly devastating."
Many of the moose develop bald spots or
are left with only sparse bits of pale
undercoat hair. The thin, pale-colored
animals are sometimes called "ghost moose."
Infestations are most dangerous for calves,
which are already vulnerable in winter.
In some areas of New England, where
infestations have swept through the
moose populations, winter ticks have
killed more than three-quarters of the calves.
The ear of a dead moose calf in northern New
Hampshire shows attached ticks so engorged
with blood they are the size of grapes.
(Henry Jones / University of New Hampshire
A load of more than 40,000 ticks will use up a
calf's entire blood supply in four weeks, Pekins
said. "They get anemic, they have declining weight
too, and that's just the end of them," he said.
Adult moose are more likely to survive, but
reproduction has been affected, with far
fewer cows giving birth to twins, he said.
Although elk and deer are also infected,
they are less harmed by the ticks because
they groom their bodies regularly and are
better able to remove the parasites, Pekins
said.
The spread of winter ticks is aided by the
warming climate, according to Pekins and
other scientists.
Because of the timing of ticks' life events,
higher temperatures, earlier springs, later
winters — the pattern in a warming world —
help them survive, proliferate and attach to
moose.
Adults females drop off animals in the
spring to lay eggs, Pekins said. For an
egg-laying female tick, "Her survival is much
higher if it's bare ground than if it's 2 feet of
snow," he said.
The resulting larvae climb up vegetation and
cluster together in the fall in big balls, which
passing moose or deer can pick up — and
they are affected by the timing of winter's
arrival, Pekins said. "The first snow event
is key to killing the larval ticks that are up
in the vegetation," he said.
As in New England state and winter-tick
infested Midwestern states like Minnesota,
shorter winters are cited as a reason for
the spread in Canada.
For Yukon wildlife, winter ticks have been
most prevalent so far among elk, though
they are found on moose and deer, territorial
officials report.
A cow moose in northern New Hampshire shows hair
loss typical of tick-infested animals now called “ghost
moose.” Tick-infected moose scratch away their dark
overhairs to leave only pale strands underneath. Moose
in this part of New England have been found with an
average of 40,000 ticks, some with thousands more.
(Dan Bergeron / University of New Hampshire)
In the Northwest Territories, tick-infected "ghost
moose" were first documented in the 1980s, and
cases have increased since then.
They have spread as far north as 66 degrees latitude
in the territory's Sahtu region, and have also been
found on caribou, according to biologists' reports.
The Arctic Circle is about 66 degrees north latitude.
If infested Canadian animals wander over the border
during the time of the year they're carrying winter
ticks — between September and April — that might
be all it takes to spread the problem, Beckmen said.
"They're going to drop those ticks in Alaska," she said.
Also ominous for Alaska is the result of past research,
done by Beckmen's predecessor at Fish and Game,
which suggests winter ticks can survive even harsh
Fairbanks temperatures.
Randall Zarnke, a former Fish and Game
veterinarian, and his research partners tested
some captive winter ticks, monitoring adult
females and the eggs' hatch success in three
Alaska locations, including Fairbanks; many
test subjects survived, said the study, published
in 1990.
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