Maine is home to the largest moose population in the lower 48 states. But in one of the moosiest corners of the state, nearly 90% of the calves tracked by biologists last winter didn’t survive their first year.

And the culprit? A tiny critter that is thriving in parts of Maine as the climate warms.

This story is part of our series "Climate Driven: A deep dive into Maine's response, one county at a time." Deep Dive Climate Driven

“You look at one data sheet after another of what we found in the woods on these moose and it’s the same profile every time: it is winter tick,” said Lee Kantar, the lead moose biologist with the Maine Department of Inland Fisheries and Wildlife.

Winter ticks, which are sometimes called moose ticks, have been pestering Maine moose for about a century and likely longer. But their numbers have exploded in parts of Maine, New Hampshire, Minnesota and southern Canada. It’s not uncommon for biologists or hunters to find moose infested with 40,000, 75,000 or even 90,000 ticks. Some infested moose rub themselves virtually bald trying to scrape off the irritating ticks, creating the phenomenon known as “ghost moose.”