Crayfish chimneys

Crayfish chimneys in a drying wetland at Seedskadee NWR.

Insects buzzed in the heat as our small group from the Outdoor Writers Association of America puttered around the canoe landing getting boats, paddles, and lifejackets ready for a trip around a cypress swamp. I wandered off through a muddy brown field to find some “facili-trees” in the nearby forest. On my way back to the group, a strange shape caught my eye. Parting the tall stems of dried grasses, I found a hollow tower made of mudballs. It was only about six inches tall and a few inches wide, but the discovery felt big to me. I’d never seen anything like it!

Our local guide chuckled at my excited questions, and quickly identified the sculpture as a crayfish’s mud chimney. The crayfish I catch (well, the crayfish that my students catch—I let them have all the fun) in the Namekagon River of northern Wisconsin live in a world of sand, rocks, and swift water. If they built towers like this, the river would wash them away. But there are hundreds of species of crayfish in North America, and some of them are sculptors.

Even though my current local crayfish aren’t much for burrowing, I grew up in the muddy creeks and rivers of Iowa, where surely the crayfish build chimneys. My dad nicknamed me his “mud and water daughter” by golly, how had I not seen this pattern in my mud? He can’t figure it out either. There were lots of burrowing crayfish in the farm ponds and pasture creeks where he grew up in central Iowa. He’s seen them along the Turkey River of northeast Iowa, too, where I first learned to paddle a canoe. Now that I’m looking, I bet I’ll find some next time I visit home.

Journeys of discovery are fun at any age, so I burrowed through the internet for information.

Burrowing crayfish are sometimes called “land-lobsters” or terrestrial crayfish. Most crayfish are aquatic — living in ponds or streams — since they need to absorb oxygen through gills. Others simply inhabit wet ground with a high water table, and excavate burrows that flood and give them space to breathe. As they dig, they are loathe to exit their burrows and expose themselves to danger, so they roll the mud into a ball using their legs and mouthparts and brick it up in an ever-rising chimney of mud around their tunnel entrance. Only under cover of darkness will they exit their bunker and go in search of food.

Have you ever learned something new, and then suddenly started to notice it everywhere?

This September, I was once again on a paddling trip to a beautiful place. My family blew in to an island campsite on Saganaga Lake in the Boundary Waters Canoe Area Wilderness in northern Minnesota. While whitecaps crashed against our rocky landing, and the stiff breeze whisked away all available warmth from our tent sites, we bushwhacked to the lee side of the island. The goal was to do some shore fishing in a protected bay. As I stooped out of the alder thicket and onto the muddy shoreline, a strange shape caught my eye.

There, among the grasses and rushes in a mucky flat, were a few little towers of mud. Crayfish chimneys? In the Boundary Waters?

I was both surprised and stumped, and soon distracted by fishing. When the wind finally died and the sun came out, we no longer needed to seek refuge in the bay. I never even went back to snap a photo. My best guess, with some post-trip research and consultation with experts, is that the chimneys could have been made by calico crayfish, a widespread native species that is known to burrow.

Fast forward to October, when local artist Sara Balbin asked me to be part of the “Going, Going, Gone? Artists Explore Disappearing Species” exhibit at the Northern Great Lakes Visitor Center in Ashland. Sara had chosen to sculpt the endangered Hine's emerald dragonfly, and asked me to write a few words about its ecology to pair with her artist’s statement.

I discovered that these rare dragonflies with brilliant green eyes live in shallow wetlands on dolomitic limestone bedrock, and Door County is their last stronghold. What’s more, as their wetlands evaporate in late summer, the aquatic dragonfly nymphs retreat into the damp recesses of devil crayfish burrows! I laughed out loud when I read that — a reaction of surprise and delight. These burrowing crayfish are turning up everywhere.

Scientists acknowledge that some dragonfly nymphs may become lunch for the resident crayfish, but the relationship must allow enough of them to survive for it to be beneficial to the population as a whole. It’s important enough that crayfish conservation is recommended as an essential part of the recovery of the endangered dragonfly.

And dragonflies aren’t the only ones who find refuge with the land-lobsters. Federally threatened eastern massasauga rattlesnakes have been found hibernating in crayfish burrows, and it’s likely that the damp habitat helps them avoid both freezing and desiccation.

I’m definitely not alone in my appreciation for mud.

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