View crayfish in the field guide.
Among the largest and most common invertebrates in Missouri's lakes, streams, and wetlands, crayfish often appear in densities of around 20 animals per square meter of stream surface area. This abundance, which is greater than almost anywhere else in the world, is good news because crayfish possess many traits that make them critical to the proper functioning of our water bodies. Crayfish are also an important food for more than 200 other animals, serving as the main forage for some of Missouri’s most popular sport fish. Aside from contributing to Missouri's ecological function and natural diversity, crayfish serve industry and culture in the form of fish bait and freshwater seafood. Crayfish feature in Cajun and other traditional cuisines.
It can be hard for nonscientists to identify crayfish species. The only identification aids available in many states are highly technical keys that place heavy emphasis on slight differences in reproductive structures (gonopods) in mature males. Fortunately, Missouri crayfish have more readily observed features that can be used in determining the species. Also, many have definite and quite limited distributions, reducing the number of species from any given area that need to be considered in the identification process.
At first glance, most crayfish look pretty much alike, but closer study reveals that the species differ greatly in size, color, and the proportional development of various body parts. These differences are in turn related to the diversity of habits that crayfish have adopted to find food, reproduce their kind, and avoid being eaten by predators such as fish, birds, and mammals.
Let's compare two species of Missouri crayfish to illustrate these differences. The longpincered crayfish (Orconectes longidigitus) is one of the largest North American species, achieving a length of six inches or more from the front of its head to the tip of its tail. In contrast, the Neosho midget crayfish (Orconectes macrus) rarely exceeds two inches in the same dimension. The longpincered crayfish is olive-tan, trimmed with bright red, and its pincers are dark blue-green, prominently studded with yellow knobs. The Neosho midget crayfish is a subdued mottled brown and black color, without bright markings or knobs.
The difference in build between them suggests the difference between a bulldog and a greyhound: The stout build and short, heavy pincers of the Neosho midget crayfish contrast sharply with the more slender build and long, narrow pincers of its larger relative. The Neosho midget crayfish is bite-sized for any goggle-eye or bass, and it avoids being eaten by burrowing in rocky shoals with its powerful pincers. An adult longpincered crayfish can mount a formidable defense, and it boldly prowls the bottoms of bass-laden river pools at night in search of food.
The longpincered crayfish feeds on a variety of plant and animal materials, living and dead, including other crayfish. However, the Neosho midget crayfish is definitely not on its menu, since these two species never occur together naturally. They occupy non-overlapping ranges in the southern Ozarks, with the longpincered crayfish confined to the White River and its tributaries, and the Neosho midget crayfish occurring in the adjacent Spring and Elk River drainages to the west.
Missouri has at least 35 species of crayfish, more than most neighboring states. Our state harbors about 10 percent of the country’s species and seven species that occur nowhere else in the world except for Missouri. Each species of crayfish occurs only in certain natural settings or habitats that reflect its special requirements; the diversity of crayfish that occur in our state results from the many types of aquatic habitats that are found here. Based on their habitats and requirements, crayfish can be divided into four broad categories:
These categories overlap to a certain extent. For example, some species occur for much of the year in seasonally flooded pools, then burrow into the bottom as these pools dry up in summer.
Missouri is divisible into four aquatic regions, each with its own characteristic group of crayfish. Some species are found in more than one region, and others have only a very local occurrence. The regions serve to identify the typical crayfish habitats and centers of abundance.
The Prairie Region is in north and west Missouri. This region supports a limited crayfish fauna of seven common species. The grassland (or prairie) crayfish (Procambarus gracilis), a burrowing species, inhabits grasslands and former grasslands, often at considerable distances from any surface water. Another burrower, the devil crayfish (Cambarus diogenes), lives in timbered (and formerly timbered) areas along the courses of streams or near ponds. The northern (or virile) crayfish (Orconectes virilis) occurs in just about any prairie stream capable of supporting crayfish. It is probably Missouri’s most widespread species. In mud-bottomed streams and shallow sloughs, it is joined by the papershell (or calico) crayfish (Orconectes immunis), and in rocky streams of the eastern prairies, the golden crayfish (Orconectes luteus) is present.
The Ozark Region is in south-central Missouri. The clear rocky streams of this region are the distribution center for 26 species of crayfish. Eight of these species have never been found outside of Missouri, and 11 others have only a limited distribution in neighboring states. Ozark crayfish are distributed according to river basins, and species that are abundant and widespread in one basin are often absent from adjacent basins. Examples are the Neosho midget crayfish (Orconectes macrus) in the Neosho (Spring-Elk) River basin, and the saddleback crayfish (Orconectes medius) in the Meramec River basin. More generally distributed species include the golden crayfish (O. luteus), and the spothanded crayfish (Orconectes punctimanus). The Missouri Ozarks harbor three species of blind, white crayfish that are restricted to cave or underground streams. These are the bristly cave crayfish (Cambarus setosus) of the western Ozarks, the Salem cave crayfish (Cambarus hubrichti) of the eastern Ozarks, and the Caney Mountain cave crayfish (Orconectes stygocaneyi), which is known from only one cave in southern Missouri.
The Lowland Region is in southeastern Missouri. This region supports a distinctive assemblage of eleven crayfish species. Most of these species inhabit swamps, sloughs, and seasonally flooded areas. Although they occur much of the year in surface waters, they exhibit a strong tendency to burrow during the drier seasons. The red swamp crawfish (Procambarus clarkii) and the White River crawfish (Procambarus acutus) are the most common and generally distributed crayfish in these habitats. They occur also in lowland streams and ditches, where they are joined by another common species, the gray-speckled crayfish (Orconectes palmeri). Other crayfish that occur at a few locations in the Lowland Region are the one-inch-long Cajun dwarf crayfish (Cambarellus puer) and Shufeldt's (or swamp) dwarf crayfish (Cambarellus shufeldtii), the slightly larger shield (or ditch fencing) crayfish (Faxonella clypeata), and the shrimp crayfish (Orconectes lancifer).
The Big River Region includes the Missouri and Mississippi rivers. Many kinds of fish are characteristic of the channels of these streams, but crayfish occur only as small local populations or stray individuals. Several crayfishes characteristic of the other regions are common in sloughs and marshes on the large river floodplains. These include the White River crawfish (P. acutus) and Cajun dwarf crayfish (C. puer) along the Mississippi River, and the papershell (or calico) crayfish (O. immunis) along the Missouri River. The devil crayfish (C. diogenes) is the common burrowing crayfish on floodplains of both rivers. Another big-river crustacean, though not a crayfish, is the four-inch-long, freshwater Ohio (or Ohio River) shrimp (Macrobrachium ohione). It was formerly abundant in the Mississippi River downstream of St. Louis but began to decline in the 1940s. The species persists today in low but stable numbers along Missouri’s border.