WILDER SIDE OF OAKLAND COUNTY
Mysterious miniature “chimneys” have emerged in wet meadows and moist lawns all across our county. They are gateways to the secret underground world of several species of crayfish, collectively known as Chimney Crayfish. Mudbugs and crawdads are two other frequently used common names for crayfish, a group of arthropods that look very much like miniature lobsters. I like to use the eye-catching title of Lawn Lobsters to describe them when writing about them, and that’s just what I did four years ago when creating text for an interpretive sign for Oakland County Parks that featured the chimney construction skills of Cambarus Diogenes, a local species commonly known as the Devil Crayfish. It is also one of the most widely spread crayfish of the United States.
Michigan has eight native species of crayfish. This, now slightly outdated, but very colorful poster from the Michigan Department of Natural Resources gives an overview of the species. NOTE: The Red Swamp Crayfish, an invasive species has now been detected in sizable numbers in Novi.
Why our common “Lawn Lobsters” build chimneys remains a point of debate, but crayfish must dig a burrow to reach the water table. I would love to interview a crayfish to ask why they build chimneys. Their answers might be amazing! There are no shortages of theories as to why they are built, and as is often the case in the world of nature, the simplest possibilities are probably the correct ones.
The crawfish has to dig a burrow if it wants to be able to submerge in water beneath the water table and something must be done with the excavated mud. What is known is they use their legs and mouth parts as tiny shovels and backhoes to dig up mud and make it into a squishy balls known as pellets. If they were to scurry across a lawn to deposit the pellets away from the tunnel, they would be extremely vulnerable to night predators – which in Oakland County would include raccoons, opossums and skunks. But if the pellets are used to build a chimney around the hole, they do not have to wander at all and the safety of the burrow entrance is always present for an immediate escape hatch. The work goes on under the cover of darkness and each pellet is taken topside and placed on the surface in a circular pattern, much like a brick layer might work. The work continues most of the night, layer by layer, and by the time the first rays of sunlight illuminate the newly constructed chimney, the crayfish has scurried back down into its underworld of tunnels. Some of the chimneys are extremely well crafted structures that might be over six inches tall, while others lean a bit and look like the work of an apprentice chimney builder, working without much guidance or sleep.
A human observer may notice that some of the colors and textures of the chimney vary slightly. That is easily explained, for as the crawfish burrows down, it brings up soil from different layers of soil with different textures and colors. “Grayish mud” remains the most common color of the “smoke-stack” looking things, as some people refer to the chimneys, and “squishy” remains the common texture. Once completed, the chimneys serve as the entrance to the tunnels that may descend two or three feet down and then branch out to side tunnels and burrows. Some scientists think the chimney assists in airflow down the burrow and that would increase the amount of oxygen being absorbed by the subterranean water within the tunnels. During times of drought and extreme heat, the chimney would certainly shade the tunnels and perhaps keep life more comfortable for the crayfish.
It goes without debate that their handy work is impressive. It draws attention from humans who are puzzled when an early morning walk across their lawn reveals the freshly constructed chimneys. Almost a month has slipped by since I first noticed comments on a community Facebook page with photos of crayfish chimneys in an Oakland County lawn that were captioned rather dramatically, and incorrectly this way: “OMG! SNAKE HOLES!!!!” I jumped into the fray and identified them as the tunnel entrances of the chimney crayfish and shared the fact that snakes are not equipped to dig. I intentionally left one fact out about what might be down the holes.
Crayfish are an important components of and perhaps unsung heroes of Oakland County ecosystems because those tunnels are critical habitat for other species. Crayfish are in fact considered keystone species. National Geographic defines keystone species in an easy to understand way, “A keystone species helps define an entire ecosystem. Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether.”
What I did not share online in the Facebook debates, to avoid an endless follow up of fearful questions, is that for about five months of the year, in some areas of our county, the tunnels beneath the chimneys serve as the winter quarters for the only venomous reptile of Oakland County, the federally protected Eastern Massasauga Rattlesnake. Our rather reclusive “swamp rattlers” will sometimes seek out the burrows of crayfish. Once safely below the frost line, the rattlesnakes submerge themselves in the relatively warmer groundwater and stay in the burrow from late October until mid-April when the rising temperatures of the soil and air lure them back to the surface.
Rattlesnakes are not the only species that take advantage of the tunnels. Researchers have probed the hidden recesses of the burrows with endoscopic cameras and have even noticed frogs hibernating in the same hibernacula as our rattlesnakes. It’s almost as if the tunnels of the crayfish are the place to meet, mingle and survive, for it’s also been discovered that the Hine’s Emerald Dragonfly, one the most endangered insects in Michigan, deposits her eggs in the subterranean waters of the burrows during times of drought, a testament to the fact that that nothing in nature lives in isolation.
Now you know some of the secrets of the “lawn lobsters” and the amazing chimneys they build, another reminder that the interconnected world of nature on the wilder and urban sides of Oakland County is full of wonder.
Jonathan Schechter is the Nature Education Writer for Oakland County Government and blogs weekly about nature’s way, trails, and wildlife on the Wilder Side of Oakland County.