The Natural State is aptly named not only for its beautiful natural landscapes, but its incredible biodiversity. From rare glade-dwelling plants to salamander species found only on a few mountaintops, from prairie specialists to denizens of swamps and caves, the array of species here is astounding. Even a group that might seem rather homogeneous at first glance can be far more diverse than most might realize. No group better demonstrates that than Arkansas’s crayfish fauna. Incredibly, our state is home to nearly 60 species of crayfish, including 13 found only in Arkansas.
Perhaps best known for their pincers (chelae), crayfish are members of the order Decapoda, a group of crustaceans characterized by having five pairs of legs (“decapod” meaning “10-footed”). The first pair of legs (chelipeds) bears the pincers, which are used for several purposes, including defense, capturing food, and social interactions with other crayfish. Luckily, crayfish have an amazing capacity to regrow their pincers and other appendages, which are frequently lost due to a variety of circumstances. Behind the chelipeds are four pairs of walking legs, the first two of which are equipped with much smaller pincers that aid in feeding and grooming.
Crayfish have a segmented abdomen, consisting of seven segments, the first five of which are equipped with a pair of pleopods or swimmerets. These leg-like structures, which aid in moving through water, are much smaller than the walking legs. At the very end of the abdomen is the telson, or tail fan, which a crayfish can use a as a rudder to propel itself backwards through the water.
Crayfish breathe through plume-like gills located in the thorax. Like the gills of fish, these structures extract oxygen from the water, but the gills of crayfish are so sensitive that they can actually pull moisture from the air as well, provided the crayfish remains sufficiently moist. This is what allows crayfish to travel overland, although the degree to which crayfish are found on land varies greatly among species.
The eyes, located on the ends of stalks that can move independently from one another, give most crayfish species excellent vision. Two pairs of antennae also provide further sensory input in the form of both touch and smell. A crayfish’s mouth consists of several overlapping structures used to crush or shred its food. Most crayfish are omnivores and consume a wide assortment of foods, including plant matter, algae, carrion, insects, snails, small fish, and even other crayfish. Crayfish are in turn a vital food source for many animals that live in or near the water, including fish, turtles, wading birds, and mammals such as raccoons or mink. Most crayfish are primarily nocturnal, hiding during the day and venturing out to forage at night.
A rigid exoskeleton composed of a fibrous substance known as chitin covers the crayfish’s body. As it grows, the crayfish must periodically shed its old shell and replace it with a new one, a process known as molting. After molting, crayfish remain soft for days, a time in which they are especially vulnerable to predation.
Crayfish are found in a wide range of habitats throughout the state. Our creeks, streams, and rivers of all sizes are home to numerous species of crayfish, but so are ephemeral pools, caves, and even open areas far from permanent water where some species have made remarkable adaptations for burrowing down to the water table. Crayfish burrows are often detectable due to the presence of distinctive “chimneys” consisting of mud pushed up to the surface during the excavation process. These chimneys, most often seen during the spring, represent only the uppermost, visible portion of the tunnel system.
Several crayfish species in Arkansas belong to the stream-dwelling genus Faxonius. One of these is the beautiful Longpincered Crayfish (Faxonius longidigitus), Arkansas’s largest species and one of the largest in North America. Endemic to the White River basin of northern Arkansas and southern Missouri, it can be found dwelling in the pools of bluff-lined highland streams. This crayfish shelters during the day in crevices among slabs of bedrock or boulders and ventures out at night to search for food. It is one of our most distinctive crayfish, with its immense size and extremely elongated, slender, blue-black pincers tipped in red.
On the other extreme end of the spectrum, the diminutive Midget Crayfish (Faxonius nana) is among our smallest species. This species is recognizable due to its very compact build, short, broad pincers, and prominent dark saddle-shaped marking across the junction of the thorax and abdomen. The Midget Crayfish is endemic to a small portion of the western Ozarks in Arkansas and Oklahoma, where it is found predominantly within the Illinois River watershed.
The Ringed Crayfish (Faxonius neglectus) is one of our most distinctive crayfish, named for the black rings around its claws that offset the brightly colored orange-red tips. Arkansas is home to two subspecies of Ringed Crayfish, including the nominate form (F. n. neglectus) and the even more strikingly marked Gap-ringed Crayfish (F. n. chaenodactylus), which has additional broad cream-colored or whitish bands above the dark ones. The two subspecies are found in different watersheds in the Ozark Highlands.
The northeastern part of the state is home to several rare, narrow-range endemic species, including the Mammoth Spring Crayfish (Faxonius marchandi), the Coldwater Crayfish (Faxonius eupunctus), the Spring River Crayfish (Faxonius roberti), and the Eleven Point River Crayfish (Faxonius wagneri). The latter two species were just described in 2018. The Eleven Point River Crayfish was given its scientific name in honor of Brian Wagner, the Arkansas Game and Fish Commission’s (AGFC) aquatic wildlife diversity biologist. One of the foremost experts on crayfish in the region, Wagner first recognized the distinctiveness of this form in 2005. Another Ozark endemic, Hubbs’ Crayfish (Cambarus hubbsi), belongs to the more heavily built genus Cambarus. This stout species is olive-tan to greenish in coloration and has broad, powerful pincers. Hubbs’ Crayfish is thought to be longer-lived and slower-growing than many other stream crayfish species.
The Red-spotted Stream Crayfish (Faxonius acares) is found only in Arkansas, where it is restricted to streams in the Ouachita Mountains and is easily recognizable by the parallel rows of large red spots on its abdominal segments. The Little River Creek Crayfish (Faxonius leptogonopodus), is restricted to the Little River basin of southwest Arkansas and adjacent southeast Oklahoma. Some populations of this species show an intricate pattern of leopard-like spotting on the carapace. The Ouachita Highlands are also home to the Western Painted Crayfish (Faxonius palmeri longimanus), another striking species with spotted chela encircled by blue-black bands tipped in red.
The Red Swamp Crawfish (Procambarus clarkii) is one of the most familiar crayfish species, as well as the most economically important – this is the main species commercially harvested for human consumption. This species, which grows quite large, inhabits swampy lowland areas of the state, such as sloughs and oxbows. In these habitats you can also find some of the smallest crayfish in the state, such as the Swamp Dwarf Crayfish (Cambarellus puer) and Ditch Fencing Crayfish (Faxonella clypeata), as well as some of the strangest, such as the Shrimp Crayfish (Faxonius lancifer). Lowland areas with a high water table are also home to a variety of burrowing species, including the Painted Devil Crayfish (Lacunicambarus ludovicianus), easily recognizable due to the bright red lining on its carapace.
Due to their secretive nature, the life histories and distributions of burrowing crayfish are often poorly understood. The state-endemic Boston Mountains Crayfish (Cambarus causeyi) is found only in the Boston Mountain ecoregion of north-central Arkansas, where it excavates tunnels in the rocky soil, often beneath boulders in roadside ditches. The Osage Burrowing Crayfish (Procambarus liberorum), a regional endemic, has one of the most unusual discovery stories – it was first discovered by a cat! It was first described in 1978 from three specimens caught by a cat in Bentonville. Other species have been discovered more recently, including the Caramel Crayfish (Fallicambarus schusteri), described in 2015 and known only from a handful of roadside ditches in extreme southwest Arkansas and adjacent southeast Oklahoma.
Still other Arkansas crayfish exhibit even more drastic adaptations to extreme environments. Arkansas is home to three species of highly specialized cave-dwelling crayfish – the Benton County Cave Crayfish (Cambarus aculabrum), the Bristly Cave Crayfish (Cambarus setosus), and the Hell Creek Cave Crayfish (Cambarus zophonastes). Species that live in caves have a number of special adaptations, including the loss of pigmentation, greatly reduced eyes, and low metabolic rates.
These are just a handful of the crayfish species that call Arkansas home, and as you can see, new species are still being discovered right here in our own backyard. The next time you’re exploring the outdoors and come across one of these fascinating creatures, take a closer look and think about the amazing diversity all around us. But don’t get pinched!