Frozen Beetles: The Mystery Continues

Those of you who have followed this blog for a long time might remember that I’ve speculated several times about the phenomenon of finding various insects frozen in the ice on wetlands and ponds. About two years ago, I even conducted a rigorous (?) scientific experiment to see whether those insects were dead or just temporarily frozen. You can revisit that post here, if you’re interested. Spoiler – they were most definitely dead, but I had fun with the analysis anyway.

As a result of my continued exploration of this topic, I think I can confidently say that most insects – especially terrestrial insects – found frozen in wetlands and ponds are dead. But why and how they got there is still uncertain. Today, I added to that uncertainty.

I stopped for a quick visit at a frozen wetland in one of our relatively recent prairie/wetland restorations. It had been warm over the weekend, and then had fallen back below freezing during the early part of this week. As a result, I figured there might be some interesting patterns in the ice. This is what passes for entertainment in my world.

This large beetle was waiting for me when I arrived at the frozen wetland today.

Shortly after arriving, I spotted a big black beetle – head down and half encased in ice. Based on how often I see frozen insects in the ice, that wasn’t a big surprise. What’s more interesting is that I’ve visited this same wetland maybe a half dozen times over the last couple months. During that time, I’ve explored its frozen surface pretty extensively and have not seen a single frozen insect. Today, I found numerous frozen insects of various species, along with quite a few snail shells. Why now?

My first thought was that maybe the insects had been frozen in the lower layers of the ice for a while, but had just been revealed now because of the melting that happened over the weekend. That doesn’t make any sense, though, because I’ve watched the surface of this same wetland swale freeze and thaw several times this winter. I saw a lot of grass seeds on the ice today too – especially from prairie cordgrass (Spartina pectinata) – which I assume was a result of yesterday’s winds. Maybe the insects had been lying dead on the edge of the wetland and were blown onto the ice by those same winds. But, if so, why hadn’t I seen them at other times during the winter after other windy days?

I also found this cute little green beetle.
This isopod (aka sow bug, roly poly) was encased in ice next to some frozen bubbles.

I suppose it’s possible that the insects were overwintering nearby in thatch or below ground and then ‘woke up’ for a while during the warm weekend. If so, they could easily have wandered out onto the melting ice and gotten stuck, either in pools of melt water or by overnight refreezing. In fact, this is my best hypothesis. But it still doesn’t explain why I haven’t seen insects on previous visits because we’ve had plenty of warm days followed by cold snaps.

I don’t get it. But, as I’ve said many times before, there are plenty of other things I don’t understand about prairies, wetlands, and the species that live in them. It’s part of why I continue to enjoy exploring them. And since there’s no possibility that I’ll ever learn everything there is to learn about this ecosystem, I guess I’ll get to keep happily wandering around them for many more years – being extra careful not to get stuck out on the ice…

Photos of the Week – January 31, 2020

We got some light snow this week. Then, as soon as the sun came out, that snow began to melt. I was on a conference call when the sun emerged and I had a hard time sitting still during the remainder of that call… As soon as we signed off, I was out the door and heading to our family prairie, hoping to get there before the snow disappeared. I made it, but just barely – I could almost see the snow patches shrinking as I walked around.

We don’t normally have a stream on the property, but the ‘drain’ that leads to the pond was full of water – the result of recent rains and snow melt perched on the frozen ground. Judging by tracks, the consistency of the slushy ice in the so-called stream was just enough that the raccoons could almost run across the top. The exceptions, where the tracks suddenly got much deeper and filled with water, revealed a story that would have been entertaining to watch in real time.
I wandered between patches of tall and short vegetation, looking for tracks and other signs of life and activity.
Coral berry (Symphoricarpus orbiculatus) in a snow bank.
There were lots of small mammal tracks, especially where vegetation was short. Ok, maybe it was just easier to see the tracks in those open areas, but it really did seem like they were more abundant where vegetation was sparse.
The best story I found was this one – here’s my interpretation. A mouse was hopping from the top left of the frame toward the bottom right. As it reached the bottom of the frame, it must have spotted the hawk (owl?) coming at it and suddenly reversed its course. It made it about three feet before the raptor swooped in from the top right and snagged the mouse where you see the wing print (and where the mouse tracks end). The raptor then ‘bounced’ once and landed in the center of the frame, where it shuffled forward a little while it either got a better grip on the mouse or consumed it. You can click this image to see a larger version of it.
More mouse tracks. I didn’t see any indication that this particular mouse was caught by a raptor.

Winter prairies, as my last post discussed, can seem empty of life at first glance. Certainly, there is much less going on than during the chaotic revelry of the summer, but fresh snow can help reveal some of what’s actually happening. I didn’t come away from this trip with the kinds of photos I was hoping for, but it’s hard to complain. The tired adage about ‘a bad day fishing’ applies here too, and I fully recognize the privilege I enjoy that often allows me to drop everything and head to a prairie at a moment’s notice.

The stories hidden in winter prairies are fewer and harder to find, but that also makes them more gratifying to discover. If you’re fortunate enough to live where fresh snow reveals stories in prairies near you, I hope you’ll be able to go on your own expedition.