Where Snowpack Meets Soil: An Important Winter Home For Bugs

IRA FLATOW: This is Science Friday. I’m Ira Flatow.

KATHLEEN DAVIS: And I’m Kathleen Davis.

By now, a large amount of the US is in spring. Meaning the snow has largely melted away and temperatures are rising. And you may have noticed that insects are coming back out. Insects don’t all just die away in the winter. Many species wait out the season in a secret place that lies underneath the snow pack, but above soil. This is called the subnivium.

New research has come out that sheds more light onto this mysterious ecosystem. And joining me now is the lead author of that study, Chris Ziadeh, who did the study as a graduate student of the University of New Hampshire, in Durham.

Welcome to Science Friday, Chris.

CHRIS ZIADEH: Hi, Kathleen. Thanks for having me on today.

KATHLEEN DAVIS: So help me picture this subnivium. What does it look like?

CHRIS ZIADEH: Yeah. So the subnivium is a space that forms under the snowpack. It occurs right between the bottom layers of the snow itself and the ground. It’s not a very large space, probably just measuring like an inch or two in height depending on environmental conditions, but it runs along all areas where there’s sufficient snowpack present. The subnivium forms because heat is generated from the ground and it melts those bottom layers of snow directly adjacent to the ground.

I know the subnivium is kind of a difficult thing to imagine, but if you go out into the snow in the winter and you’re walking around, wherever you step, you can actually reach down where your foot was just at and feel around, and you should feel a space right between the ground and the snow. And that’s the subnivium.

KATHLEEN DAVIS: Oh. So is the snow on top of the subnivium kind of working like a warm blanket, per se?

CHRIS ZIADEH: Yeah. So the subnivium is dependent on that snowpack, as you said, to act as a warm blanket. The conditions are kind of strange down there in the subnivium. It’s stays right around 0 degrees Celsius, right around freezing, and about 100% humidity. The conditions may not seem ideal to me or you, especially the near freezing aspect of it. But it’s far better than the conditions typical of the ambient winter conditions, very much more warmer than ambient conditions, and temperatures don’t fluctuate as much down there because of that snowpack.

KATHLEEN DAVIS: And it sounds like some creatures actually thrive in the subnivium. I mean, what do we know about what life is like down there?

CHRIS ZIADEH: Yeah. So like I said, it’s right around 0 degrees Celsius. So right around freezing. It’s quite humid down there. And there’s actually not a lot of sunlight penetrating through the snowpack there. So it’s probably pretty dark. And conditions remain constant down there, which is why these arthropods seem to do so well compared to the ambient conditions. Because if they’re out and about in the ambient conditions of winter, they wouldn’t do so well. But in this subnivium, it remains constant in there. They seem to be pretty happy.

KATHLEEN DAVIS: And what exactly is an arthropod?

CHRIS ZIADEH: So an arthropod is insects or insect-adjacent animals. So essentially, what I usually say is anything that crawls along the ground and doesn’t have a spine is likely an arthropod. So think spiders, centipedes, beetles, all fall underneath the realm of arthropod.

KATHLEEN DAVIS: OK. So originally I was sort of imagining a big bug party, with maybe some tasty treats for our arthropod friends in the subnivium. Do we know if it’s a particularly active place?

CHRIS ZIADEH: Yeah, it’s probably not an arthropod party. But yeah, arthropods are dependent– they don’t regulate their temperature very well– their body temperature. And so they’re dependent on environmental temperature. And so when it’s cold, like it is in the subnivium, they become quite lethargic. And so they’re rather slow. So whatever they’re doing down there, they’re doing it very slowly.

KATHLEEN DAVIS: OK. So let’s talk about this study that you did, where you looked at the types of species that we’re likely to find in the subnivium. What did you find?

CHRIS ZIADEH: Yeah. So we collected quite a variety of different arthropods in the subnivium. Some of the taxonomic groups that were pretty common include things like spiders, beetles, centipedes, mites, and springtails, just to name a few. We also found quite a few immature arthropods down there. So arthropods that are in earlier life stages.

KATHLEEN DAVIS: So are new arthropods being born in the subnivium?

CHRIS ZIADEH: Yeah. So arthropods are doing whatever they typically do. Whatever you imagine arthropods do in the summer, they’re also doing in the subnivium. So they’re continuing to move around, feed, search for mates, breed, avoid predators. Everything associated with an arthropod’s life cycle is also occurring down in the subnivium.

KATHLEEN DAVIS: And I think that this is really interesting because I think there’s a myth out there that people who aren’t super familiar with insects might think, OK, the winter rolls around and all the insects die. But that’s not true, right?

CHRIS ZIADEH: Yeah, I also used to think that. Growing up, I thought that all the arthropods just kind of die out when winter rolls around. And we think that just because they disappear from our sight. They’re no longer part of our everyday lives, so they must be dead. But in reality, they seek out refuge in places like under the bark or in the mud of lake bottoms and in the soil and in the subnivium and in leaf litter on the ground.

So not only do some summer arthropods overwinter in the subnivium, one of our main findings was that there’s actually arthropods that only come out in the subnivium, which was quite interesting.

KATHLEEN DAVIS: Oh, interesting. So you were doing this study specifically in your neck of the woods, which is New Hampshire. I mean, can we presume that the species that we would find in the subnivium would be the same maybe in other states?

CHRIS ZIADEH: Yeah. I mean, you would probably find similar groups. The specific species would probably vary. But you’d probably find the same type of characters. So spiders were quite common in the subnivium in northern New Hampshire here. But, let’s say, in Vermont or further west, there might be some different spiders active. But I would guess that they are probably pretty close taxonomically and probably serve a lot of the same functions as the spiders here in New Hampshire in the subnivium.

KATHLEEN DAVIS: So there’s always a little bit of an elephant in the room when we’re talking about cold weather. And that is climate change. So do we have any idea how climate change might affect these insects that rely on the subnivium to wait out the winter?

CHRIS ZIADEH: Yeah, that’s a great point. That’s why I wanted to do this study is because climate change is an ever-present threat. And snowpack is obviously going to be affected by climate change. And these arthropods, like I mentioned before, are dependent on that deep snowpack during the winter. And so, with climate change decreasing that snowpack, these arthropods might experience more harsh conditions than they otherwise would.

It might seem counterintuitive that as temperatures increase that these arthropods will experience harsher, colder conditions. But without that deep snowpack there to insulate them, they’ll be exposed to the ambient conditions. And so yeah. So as temperatures rise, these arthropods will actually likely experience colder conditions.

KATHLEEN DAVIS: So in that case, how many of us assumed where all the insects died in the winter, that might actually be closer to reality?

CHRIS ZIADEH: Yeah, unfortunately, it’s likely that a lot of those arthropods in the subnivium won’t deal with this change well. Some of them might. It’s kind of speculation at this point. But yeah, removing that snowpack probably doesn’t bode well for most of them.

KATHLEEN DAVIS: There’s this bigger crisis of insect biodiversity loss, right? I mean, I feel like we are hearing all the time about different species that are going extinct.

CHRIS ZIADEH: Yeah. And that’s another main driver behind this study was this idea that’s going around in the entomology world right now. It’s kind of a hot topic. One of the main drivers of the study, along with climate change, was this idea that’s floating around the entomology world right now is insect decline. As you know, a lot of organisms are declining due to human activities. And it’s feared that we’re losing a lot of our insect abundance and our insect diversity. And a lot of this is going unnoticed because they are such small organisms that we just don’t see them disappearing.

And there was a couple of studies done here in New Hampshire that correlated insect decline with snowpack decline– just loosely correlated those. And that’s why I wanted to look at the organisms that would be most affected by snowpack decline– the insects that would be most affected– those that depend on the snowpack itself.

KATHLEEN DAVIS: Do you think, generally, that arthropods are not appreciated as much as they should be?

CHRIS ZIADEH: I do think that people don’t really appreciate arthropods as much as they should. Even if you don’t spend a lot of time thinking about arthropods, like most entomologists do, they do play an important role in our everyday lives and to the health of our forests. Most people know the importance of pollinators. But beyond that, maybe they don’t think about the roles of other arthropods very much. Many arthropods serve important roles in decomposition and nutrient cycling. They are important components of food webs. And some arthropods help keep pest populations low.

So even if you don’t think about arthropods often, they are important components to just about every aspect of our forests. And if arthropods continue to disappear, whether due to climate change or snowpack decline or some other reason, then there will be noticeable changes to things more visible to us, like our trees and our birds and many other things.

KATHLEEN DAVIS: A good case for protecting our arthropods. That is all the time that we have for now. I’d like to thank my guest, Chris Ziadeh, who did this study as a graduate student of the University of New Hampshire, in Durham. Thanks so much for joining us.

CHRIS ZIADEH: Thank you.

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