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.
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 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…