Crayfish are crustaceans belonging to the order Decapoda, which are known for having ten legs (five pairs of “walking legs,” which are exactly what they sound like). Other members of this order include shrimps, lobsters, and crabs. In fact, crayfish closely resemble small lobsters. They have many names, including crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, and mudbugs, although in Michigan “crayfish,” “crawdad,” and “crawfish” are what they are most commonly referred to as.
Crayfish are known for their small claws on the ends of each of the last four pairs of walking legs, and their two large claws on their frontmost pair of walking legs, called chelae. These claws are used for a variety of tasks, including digging, capturing prey, warding off predators and threats, displays of threat or dominance to predators or other males, and holding mates in place during reproduction. They have a strong exoskeleton, or carapace, that further protects them, which is often molted and regrown dozens of times in their lifetime to allow for size increases as the crayfish matures.
They have notably segmented bodies (collectively called the abdomen) and a head that is joined to their thorax, known as the cephalothorax. Their eyes exist terminally (see definitions one and two) on small stalks that can move independently. Their snouts are rather sharp and protruding in appearance and are used to aid in digging and turning over rocks in search of food. Uniquely feather-like gill structures along their abdomen allow them to respirate underwater, though these gills can also function on land so long as they remain somewhat moist.
Michigan’s Native Crayfish Species
Specifically, Michigan’s eight native crayfish species belong to the family Cambaridae. While some crayfish are marine, Cambaridae is the largest of the three freshwater crayfish families in the world and contains over 400 distinct species. Most of the species in this family are found in North America and Europe, though scattered other species can be found on every other continent except Antarctica.
There are also two well-known, incredibly damaging invasive crayfish species in Michigan: the rusty crayfish (Faxonius rusticus) and the red swamp crayfish (Procambarus clarkii), the former being the most widespread and the latter more recently becoming established in the state around 2017.
1) Big Water Crayfish (Cambarus robustus)
As indicated by its common and Latin names, C. robustus is fairly large for a crayfish, with a carapace length that can measure two to three inches in length, sometimes more. On each chela (large, front claw), they have two rows of bumps, known as tubercles, which run parallel to one another. Their chelae are substantial and robust. They have a smooth body meant for blending into the mud and water, preferring more neutral colors like brown, olive green, grey, or tan.
Like most crayfish, the big water crayfish is not tolerant of pollution. They can be found in well-oxygenated, clear, fairly fast-flowing streams and smaller rivers. They have been found in somewhat acidic lakes, as well. Often, they live in holes and hollows beneath large rocks in the water. They occupy most of the Lower Peninsula of Michigan and are not known to occur in the Upper Peninsula at all. They reach breeding maturity around two years of age; females can live for several breeding seasons, while males typically only spawn once before dying.
2) Calico Crayfish (Faxonius immunis)
The calico crayfish is a moderately sized crayfish averaging between 1.5 and 3.5 inches in total length. Also known as the paper shell crayfish, this species has a notably thin shell that makes it vulnerable to predators. They are secondary burrowers, meaning that they can and will create their own burrows but prefer to occupy already-made burrows created by other creatures or natural holes and depressions. They will readily hide in these burrows if threatened or when water and food conditions aren’t favorable, such as when water levels are low.
Found throughout most of the Lower Peninsula and the southwest portion of the Upper Peninsula, calico crayfish are most often found in well-vegetated, soft-bottomed streams, flooded ditches, vernal pools, and sometimes flooded grassland areas. Their tubercles are arranged along the outermost edge of each chela, and the chelae are long and narrow. Their coloring can be quite varied, ranging from black, brown, green, grey, some mottled variation of these, and can even include hues of purple or blue on their chelae.
3) Devil Crayfish (Lacunicambarus diogenes)
The devil crayfish is so named for its often deep brown or black primary coloration with vibrant red highlights, particularly on the chelae, though the entire body can also have red coloration. Its head is smooth and contains no spines, and each chela contains two or three rows of notably large tubercles on the “palm.” A medium to large-sized crayfish, the devil crayfish can have a carapace length that ranges from one to nearly three inches in length, with females being slightly smaller than males.
Originally discovered in 1852, recently in 2018 scientists found through genetic testing that this species actually is a species complex, meaning it contains multiple (in this case, three) separate sub-species. Two, L. diogenes and L. polychromatus, are known to exist in Michigan.
They readily burrow and do not live exclusively in waterbodies or flooded areas. They can be found in agricultural fields, ditches, prairies, and floodplains more often than they are found in permanent water bodies such as ponds or rivers. They can be found throughout most of both the Upper and Lower peninsulas.
4) Digger Crayfish (Creaserinus fodiens)
Digger crayfish are adept burrowers with very cylindrical bodies. Their dactyl, which is the smaller, movable part on each chela (frontmost claws), has a noticeable notch and can also possess small hairs. They are usually tones of brown and grey, making them hard to spot. Their fairly large burrows have been found to provide habitat for at least two endangered species: the Hine’s emerald dragonfly (Somatochlora hineana) and the small Eastern massasauga rattlesnake (Sistrurus catenatus). The former’s larvae hatch and mature in the burrows, while the latter hibernate through the winter in the burrows. These burrows also aid in aerating the soil.
In the Spring, these crayfish are most likely to be seen wandering about as snowmelt raises the water table to such a degree that their burrows become too saturated for their liking. They prefer to reside in forested wetlands (such as swamps) and floodplains, but can also be found in ditches, vernal pools, and slow-moving streams so long as they have ample detritus and leaf matter along the bottom. It is found throughout most of the Lower Peninsula.
5) Northern Clearwater Crayfish (Faxonius propinquus)
This crayfish is small, averaging around an inch in length or less. Most often brown or tan, the northern clearwater crayfish can have some red or orange highlighting on their chelae and legs, though this isn’t incredibly common. Their chelae have some scattered groupings of tubercles along their inner edges. These crayfish closely resemble the invasive rusty crayfish, and in fact have been found to hybridize with them which has led to some concern about the eventual possible demise of F. propinquus populations as a result.
The northern clearwater crayfish is widespread in the state, able to be found in both fast-moving and more stagnant bodies of water throughout the entire state. They are quite poor at burrowing, and as a result greatly prefer rivers, lakes, streams, and ponds that have ample vegetation, rocks, and pebbles for them to hide amongst. Since they lack much ability to burrow, this species becomes at risk of drying out during times of low water levels or drought.
6) Paintedhead Mudbug (Lacunicambarus polychromatus)
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Closely related to the devil crayfish, the paintedhead mudbug looks quite similar but generally has overall lighter tan coloration with bright red or orange outlines on their rostrum (the nose and mouth area), chelae, and occasionally on their tail. They have small tubercles that are strewn all across their chelae. They have quite large and powerful claws, often with blue and green hues, which enable them to burrow quite adeptly.
They are found primarily in the southern half of the Lower Peninsula and prefer a more terrestrial life than many of their relatives. They are not often found in permanent bodies of water, but instead prefer agricultural fields, ditches, floodplains, damp meadows, streambanks, and occasionally more suburban areas. Their burrows can be identified by a tall “chimney” of dirt, out of which you might be able to glimpse their large, colorful claws poking out as they wait for passing prey, which often includes worms and insects.
7) Virile Crayfish (Faxonius virilis)
The virile crayfish is another species that has been known to hybridize with the rusty crayfish, and as such is at risk both from this and being outcompeted by its invasive relative. Virile crayfish can grow quite large – up to 5 inches in length! They have long, narrow chelae that are small compared to their overall body size. They usually have a grey, brown, or olive-toned carapace and their claws may have slightly blue or green hues which can appear greyish, often with notably large, yellowish tubercles.
Found broadly throughout the Upper and Lower peninsulas, virile crayfish are quite hardy and adaptable. As such, they are found in small and large rivers and streams as well as lakes, ponds, and the massive Great Lakes themselves. They prefer locations with rocky substrates but can also be found in more soft-bottomed, vegetated areas if they are forced out of their territory by other virile crayfish or invasive and aggressive red swamp crayfish. Their populations are at risk as red swamp crayfish continue to grow in number and spread across the state.
8) White Water Crayfish (Procambarus acutus)
The white water crayfish is perhaps most easily identified by its chelae, which are the longest, thinnest, and smallest in comparison to body size of any of the Michigan crayfish species. Their colors are often dark-hued and range from various shades of black, olive and tan, to brown, red, or yellow. Regardless of their overall coloration, their chelae tubercles are exclusively black. They are a medium to large crayfish, averaging between two and five inches in length. They closely resemble the invasive rusty crayfish, but look for the black tubercles to distinguish the two as rusty crayfish do not possess these!
White water crayfish are most often found in slow-moving to stagnant water bodies included various types of wetlands, slow streams, and inundated ditches. Though their range is not extensive and seems to be restricted to the southernmost portions of the Lower Peninsula, they are abundant where found.
They have been found to be excellent hosts for the harmful fluke Alloglossoides caridicola and the parasitic worm Alloglossidium dolandi, so it may be a boon that these crayfish do not have an extensive range as these parasites can spread to other P. acutus populations as well as to other crayfish species. The Alloglossoides caridicola fluke in particular seems to greatly favor white water crayfish as hosts, taking up residence in their antennal glands. Thankfully, these parasites appear to only live seasonally so the threat to these and other crayfish may be minimal.
