Every other Friday, the Outside/In team answers a listener question about science and the natural world.
This week's question comes from Moriah in Waterbury, Vermont.
"How the heck are ticks getting so bad even when we have these wicked cold winters?"
Producer Justine Paradis tucked her pants into her socks to find out.
Transcript
This has been lightly edited for clarity.
Justine Paradis: I’ve had the thought myself. It’s deep winter. The ground is hard as a rock. It’s yet another polar vortex. But, at least I can comfort myself that this means next summer, there will be fewer ticks. Right?
Laura Ferguson: The answer to that to some extent is sort of famous biology answer, which is just... it depends!
Justine Paradis: This is Laura Ferguson, a biologist at Acadia University in Nova Scotia. She studies how insects like ticks and mosquitoes respond to environmental change. And she said…
Laura Ferguson: Yes, ticks will die if they get too cold.
Justine Paradis: If only the conversation ended there. Laura says they see ticks dying off when they’re exposed to the wicked cold for prolonged periods. Specifically, below -10 degrees Celsius. But the thing is, ticks are very good at not getting cold.
Like many insects, ticks tuck themselves in for the winter in piles of leaves, where the layer of air pockets provide really great insulation, much like a puffy coat. If it happens to snow, well, even better. Snowpack is just another layer of insulation which keeps them even cozier.
The temperature difference here can be huge. During a recent polar vortex in Nova Scotia, Laura actually decided to measure it herself.
Laura Ferguson: And I think we hit -26 degrees overnight and Celsius. And then underneath that leaf litter and snow cover, it was minus six for maybe an hour. That was as low as it got.
Justine Paradis: Hear that? Under the leaves, it never even hit that -10 wicked cold threshold. Meanwhile, physiology-wise, ticks are hardcore.
Laura Ferguson: Sometimes they're producing what we call cryoprotectant molecules. These are molecules that maybe act a little bit like, say, antifreeze in your car.
Justine Paradis: These molecules lower the freezing point of fluids inside ticks’ bodies.
Unfortunately, it gets worse. Black legged ticks carry many microbes; notably, a bacteria called Borrellia burgdorferi, which causes Lyme disease in humans. A few years ago, Laura and her colleagues wondered: how does this Lyme-causing bacteria impact a tick’s ability to survive the winter?
Laura Ferguson: And we did find that for three years in a row, ticks that were infected with Borrelia burgdorferi tended to be better at surviving the winter.
Justine Paradis: I think I speak for a lot of us when I say: you've got to be kidding me. They don’t know why this Lyme-causing bacteria appears to help ticks survive the winter. So far, Laura says, it doesn’t seem to help them withstand the cold better. But, maybe it helps the tick manage its energy stores to hold out without eating all winter. Or maybe it compels the tick to change its behavior. There are still a lot of questions.
Laura Ferguson: What might those things be doing to the ticks? You know, is the tick sick? Is it changing the way it behaves to cope with the fact that it’s carrying this particular microbe around? Is being infected, making you better at pushing that northern range edge further and further? Which is what we've been seeing happening over the last couple of decades.
Justine Paradis: So, probably not what most of us want to hear when it comes to ticks and winter. And the Lyme bacteria appears to be making our coexistence with ticks more challenging… in more ways than one.
If you’d like to submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org. You can also leave a message on our hotline, 1-844-GO-OTTER.
