St. Francis River Crayfish

Media
Photo of a St. Francis River crayfish.
Status
Name
Species of Conservation Concern
Scientific Name
Faxonius quadruncus (formerly Orconectes quadruncus)
Family
Cambaridae (freshwater crayfish), in the order Decapoda (shrimp, crabs, and lobsters)
Description

The St. Francis River crayfish is a medium-small crayfish. It is brown, with blackish blotches and specks on the dorsal surface of the pincers and body (the specks are most numerous on the abdomen). The pincers are often trimmed with red, and thickly set hairs (setae) are present in the gap at the base of the fingers.

Similar species: The only other small brown native crayfish within the general range of this species is the Big Creek crayfish. The two species cannot be separated with confidence without comparing the male reproductive structures (short and blunt in the St. Francis River crayfish; long and slender in the Big Creek crayfish). The two species are rarely found in the same stream.

The woodland crayfish, which has been introduced into the St. Francis River drainage and is invasive in that drainage, is distinguished by its own pattern of blotches and speckles.

Size

Adult length: about 1¼ to 2½ inches.

Where To Find
St. Francis River Crayfish

The St. Francis River crayfish occurs only in Missouri, in the upper St. Francis River and its tributaries (mostly exclusive of Big Creek and other streams supporting populations of the Big Creek crayfish), in St. Francis, Iron, Madison, and Wayne counties. It has been collected in the same stream as the Big Creek crayfish in only a few locations.

Lives in clear, rocky streams, ranging from small headwater creeks to moderately large rivers. Prefers silt-free bottoms near or beneath dense beds of water willow or boulders. Its burrows are dug in gravelly substrate beneath rocks. Its distribution largely complements that of Big Creek crayfish; the two species might compete because of similarities in habits and habitat.

Crayfish are generally omnivores, eating a wide variety of plant and animal materials.

Imperiled; a species of conservation concern. The St. Francis River crayfish occurs only in Missouri (it is endemic to our state), with a localized distribution that has shrunk in past decades.

This species was first described from specimens collected from Stouts Creek at Ironton in 1931, where it was reported the species was very abundant. Since then, however, the woodland crayfish was introduced to that stream and has replaced them. This illustrates why crayfish should not be released anywhere except from where they were originally collected.

Life Cycle

Like other Ozark stream crayfish, this species has both a fall and a spring reproductive season. In their first year, young will reach 1 to 1½ inches in length, but few of these become sexually mature in their first year. Both males and females grow at different rates, but eventually reach the same maximum size. Most St. Francis River crayfish don't live more than two years.

Crayfish feed many types of wildlife, including many species that humans hunt and fish. Crayfish commonly serve as bait, plus many people eat crayfish, too. Crayfish are fascinating, colorful creatures in their own right and are part of our rich natural heritage.

Their opportunistic, omnivorous feeding makes them an important link in the food chain between plants and vertebrates, breaking down plant and other materials that are resistant to decomposition. Crayfish in turn are an important food for many other animals.

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About Aquatic Invertebrates in Missouri
Missouri's streams, lakes, and other aquatic habitats hold thousands of kinds of invertebrates — worms, freshwater mussels, snails, crayfish, insects, and other animals without backbones. These creatures are vital links in the aquatic food chain, and their presence and numbers tell us a lot about water quality.