Flying Cat Circus: Stoneflies

There are around 1600 species of stoneflies in the world, 450 of which are to be found in North America, and yet I found that I knew next to nothing about them. I suspect I’m not the only one, and I hope to remedy that with this Things from the Shelf.

I recently went on a tubing trip with my dad down the Apple River. The weather cooperated, the river was clear, and we only had one spot where we had to get out and clamber over a fallen tree. The only problem I encountered was the fact that my tube had sprung a leak, so I could hear it bubbling the entire trip and I was riding about five inches deeper by the time we pulled out.

Otherwise, it was great. The Apple River that runs through my grandfather’s land is beautiful, with trees lining the riverbanks on either side and deep fish ponds where I could flail free of my inner tube and dive. There were a few close calls—I nearly got taken out by a duck house that was staked in the middle of the river—and some of the fallen trees that we passed underneath were close enough that we had to lean in order to slip under.

There’s a lot of wildlife out there on the river, secluded from human civilization as we were. My dad acquired a spider passenger after we went under a log at one point—I’m thinking it was some sort of orb weaver—and there were swarms of damselflies of all colors ranging along the banks that would alight on your arms or legs if you sat very still as you went by.

Now, as we were passing some rocks not far from the park where we pulled out, I noticed that the rock was peppered with little gray shapes. I was waiting for my dad to get through the rapids, so I anchored myself on the rock and took a closer look to pass the time, and found that they were stonefly sheds. Stoneflies, for those who don’t know, are very closely related to the cockroach. They’re long of body—from six to fifty millimeters in length—with long, veined, transparent wings that fold up crosswise over their back, hence their scientific name—‘Plecoptera’ meaning ‘twisted’ in Greek.

What I was finding was the sheds from the partially-grown naiads. Stoneflies go through what is known as incomplete metamorphosis, meaning they don’t make sudden, definite shifts from one stage in life to another like a caterpillar metamorphosing into a pupa and on into a butterfly. Instead, they develop gradually into an adult over a period of instars—growth stages between sheds—until their wings have fully developed and they can leave on their mating flight. The naiads look a lot like the adults, save without wings. They have a wide, flat head, a three-sectioned thorax, and a segmented abdomen from which branches a pair of tails (or ‘cersi’). The wings begin developing partway through their metamorphosis as little sacs on their backs, and will grow steadily until they reach their adult stage.

The adult stoneflies deposit their eggs in fast-moving rivers, so the naiads naturally must be adapted for life on the river bottom. Their bodies are flat, with the strong, anchoring legs splaying out from the sides so that they can cling to rocks in fast currents and let the water rush right over them. They’re also equipped with gills, which appear as tiny, hair-like structures growing on and around the thoracic region, mostly where the legs meet the body. They anchor themselves on rocks in the center of the current, and seem to prefer fast, cold, highly oxygenized water. If there isn’t enough oxygen for them to breathe, they’ll perform ‘push-ups’ in order to move more water over their gills.

When the adults hatch, they don’t have much for mouthparts. They will have chewing mandibles, but these tend to be nonfunctional since the adults usually don’t live long—from a few hours to a few days—though they do survive a little longer than the average mayfly. They immediately rise to mate, and afterwards the female will either lay her eggs near the surface of the water or dive beneath the surface to lay them on the bottom. The eggs have adapted just as the naiads and adults, and are equipped with either a sticky substance or some sort of anchor to fasten them to the river bottom. After eight to ten months, the eggs hatch, and the process starts all over again.

The sheds that I found ranged in size from an inch to half an inch, and I was told that they were small compared to what they would become later on during their metamorphosis. After my dad caught up, I decided that on the next cycle through, I would bring a jar and collect some of the sheds. I did that, and put it in a bag and tied it around my waist. After the beating I dealt it coming down the river the second time, I’m surprised it was still intact, and yet somehow I was able to not only keep the jar, but also find the rock where I’d seen the sheds and collect a good dozen or so for my shelf museum. A week later, I realized I still didn’t have a post ready for the weekend, so I pulled out the box of stoneflies and began researching.

For the most part, I found out everything I wanted, but unfortunately, there’s something I’m still curious about: How does the circulatory and respiratory system of the stonefly shift from breathing water through gills to breathing air through little holes (called ‘spiracles’)? So far, I’ve had no success with Google. If any of my readers can figure out the answer, I would greatly appreciate it if they would post in the comments section below, and I will be sure to share the answer on the blog for all to see.

Happy reading!

S. R. Koch