Ecosystem Engineers: Burrowing Crawfish Create Vital Habitat

by Zach Truelock, Herpetologist

A painted-hand mudbug in its burrow on a wetland preserve owned by Sycamore. Photo by Zach Truelock

While walking through a field, perhaps near a stream, pond, lake, or ditch, you may have seen tall muddy chimneys, clustered and towering over the ground. They’re unique and eye-catching on the landscape—and can be dense enough to appear as a tiny city made of muddy skyscrapers.

So, what are these things? Their architect is reclusive and rarely seen, but on rainy nights you may be lucky enough to see a pair of claws and antennae protruding from the entrance.

Crayfish, crawfish, crawdads, mudbugs—whatever you call them, these charismatic crustaceans form an integral part of the North American landscape. We are in a crayfish hotspot—nearly 70% of the approximately 500 species of crayfish in existence are native to the waters of North America. Much of this crayfish diversity occurs in the southeast, but the Midwest also has its fair share. Though many of us are most familiar with the aquatic species found in streams, lakes, and ponds, Indiana’s 21 species are diverse in form and habitat, occurring even in places such as caves, forests, and prairies.

It is perhaps the so-called “primary burrowing” crayfish that are most interesting. How does a typically aquatic animal, that uses gills to breathe, live on land?

Simply put—they dig. Burrowing crayfish dig long burrows down to the water table so they can wet their gills as needed and keep their burrows moist and cool. Because of this, they can spend nearly their whole lives underground. It would be hard to know they even existed at all if it weren’t for the large chimney-like towers they build above burrow entrances. The crustacean’s abodes can be extraordinarily complex with multiple chambers and entrances, going as deep as 15 feet underground! Their secretive habits have long made burrowing crayfish difficult to study, but scientists are increasingly learning more about these animals and the integral roles they play in the ecosystem.

A Kirtland’s snake in a crayfish burrow. Photo by Zach Truelock

Crayfish are sometimes considered keystone species because of how many different species eat them and their role in transporting nutrients to species higher on the food chain. The same is true of burrowing crayfish, but they also serve another role: as ecosystem engineers. Just as a beaver creates new habitat by blocking a stream, crayfish burrows create habitat and refuge for an impressive assortment of species. In the upper Midwest, federally threatened eastern massasauga rattlesnakes and copperbelly watersnakes use crayfish burrows for shelter and to hibernate. The larvae of the federally endangered Hine’s emerald dragonfly use crayfish burrows to survive periods of drought and freezing. Closer to home, the state-endangered Kirtland’s snake and the crawfish frog both historically occupied crayfish burrows within the Beanblossom Creek valley—though the crawfish frog has sadly since disappeared from this area. A close association has been noticed between the habitats and range of Kirtland’s snakes and the digger crayfish, and the small Kirtland’s snake may depend on the crayfish as a prey item as well as a habitat architect. A plethora of other species will also use crayfish burrows, including countless insects, salamanders, snakes, frogs, toads, spiders, and small mammals. Their burrows also help aerate the soil and recycle nutrients back up to the surface. The incredible list of biodiversity supported by burrowing crayfish, and the ecosystem services they provide, cements their importance as a true keystone species. But they are also fascinating in their own right.

Primary burrowing crayfish burrow at a Sycamore wetland preserve on Beanblossom Creek. Photo by Zach Truelock

It’s not fully understood why crayfish build chimneys over their entrances, but burrows often contain multiple entrances, some with chimneys and some without. Creating chimneys may allow crayfish to rid their burrows of excavated soil without leaving the burrow and potentially exposing themselves to predators. Juvenile burrowing crayfish seem to take cues from burrow chimneys excavated by older crayfish of their species and preferentially make their own burrows near established ones. Recent research has revealed another function of burrow chimneys—ventilation. When wind gusts blow near burrows, air is drawn in through the chimney-less opening and flows out the top of the chimney. Since burrow water is often low in oxygen, chimney construction may be important for allowing the crayfish to respire.

Three species of burrowing crayfish call the land that Sycamore Land Trust protects home: the digger crayfish (Cresearinus fodiens), the paintedhand mudbug (Lacunicambarus polychromatus), and the aptly named Crawzilla crawdad (Lacunicambarus chimera). The next time you see a crayfish chimney, stop and think about these amazing ecosystem engineers.

Paintedhand mudbug. Photo by Zach Truelock

This article is from the Winter-Spring 2024 issue of The Twig, “The Science Issue.” Read the issue at sycamorelandtrust.org/twig.