July 01, 2019Mysterious miniature "chimneys" are emerging in moist meadows and lawns as well as along stream banks across most of Michigan; just as they do every spring and well into summer. These mysterious chimneys are not gateways to a secret underground world, but rather the homes of several species of crayfish, collectively known as Chimney Crayfish with most of the work being done by Cambarus Diogenes, a species commonly known as the Devil Crayfish. Devil Crayfish, also known as mudbugs or crawdads; are the most widely spread crayfish of Michigan.
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 then 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 they would be extremely vulnerable to night predators which would include raccoons, opossums, skunks and even owls. But if the pellets are used to build a chimney around the hole they do not have to wander and the safety of the burrow entrance is always present as 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 in the same field, and rather significantly county by county. 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 they 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 scientist 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.
In the world of nature all things are interconnected, and crayfish (lawn lobsters) are more than bait, or something to toss in the campfire stew pot. But they are tasty. Jonathan Schechter photos
It goes without debate that their handiwork is impressive and draws attention from humans who are puzzled when an early morning walk across their lawn reveals the freshly constructed chimneys. More than a month has slipped by since I first noticed comments on a community Facebook page with photos of crayfish chimneys in a suburban lawn that were captioned rather dramatically, and incorrectly in bold letters 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 component of and perhaps unsung heroes of some ecosystems because those tunnels are critical habitat for other species. Crayfish are in fact considered keystone species. Wikipedia defines keystone species in an easy to understand way, "A keystone species is a plant or animal that plays a unique and crucial role in the way an ecosystem functions. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. ... The role that a keystone species plays in its ecosystem is analogous to the role of a keystone in an arch."
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, especially in southeast Michigan, the tunnels beneath the chimneys serve as the winter quarters for the only venomous reptile of Michigan, the federally protected Eastern Massasauga Rattlesnake. Our rather reclusive "swamp rattlers" will sometimes seek out the burrows of crayfish for winter hibernation. Once safely below the frost line, the rattlesnakes submerge themselves in the 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 spotted 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 Hines 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 nothing in nature lives in isolation.
Now that you know some of the secrets of the "lawn lobsters" and the amazing chimneys they build, let that serve as another reminder that in the world of nature all things are interconnected, and crayfish are more than bait, or something to toss in the campfire stew pot. But they are tasty.