Mammoth Spring Crayfish

Faxonius marchandi (formerly Orconectes marchandi)

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Photo of a Mammoth Spring crayfish.
The Mammoth Spring crayfish has a very localized distribution. In our state, it lives only in the Warm Fork of Spring River, in Oregon County.
Chris Lukhaup
Species of Conservation Concern
Family

Cambaridae (freshwater crayfish) in the order Decapoda (shrimp, crabs, and lobsters)

Description

The Mammoth Spring crayfish is a reddish-brown crayfish with broad, powerful pincers. The pincers have numerous blackish specks on their basal parts. The abdomen is dark rust-red without specks. The carapace is light tan, with a dark brown band crossing the back of the head and another at the junction of the carapace and abdomen. This crayfish bears a striking resemblance to the Ozark crayfish, and both species occur in the Warm Fork. Males of the two species are easily distinguished by the shape of the reproductive structures (gonopods). The gonopod tips are long and slender in the Ozark crayfish, short and blunt in the Mammoth Spring crayfish. The Ozark crayfish is lighter tan and less reddish, especially on the pincers.

Size

Adult length: about 1½ to 2½ inches.

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Photo of a Mammoth Spring crayfish hiding under a rock.
Mammoth Spring Crayfish
Like many other crayfishes, the Mammoth Spring crayfish hides beneath rocks.

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mammoth spring crayfish
Mammoth Spring Crayfish
Habitat and conservation

The Warm Fork of the Spring River, where this species is found in our state, is a medium-sized, clear Ozark stream with well-defined riffles and runs. This species occurs on riffles over gravel or rubble substrate.

Foods

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

image of Mammoth Spring Crayfish Distribution Map
Distribution in Missouri

The Mammoth Spring crayfish has a very localized distribution near Mammoth Spring in the Spring River of Arkansas and Missouri. In our state it has been collected only from the Warm Fork (and two of its tributaries) of Spring River near Thayer.

Status

This may be Missouri’s rarest crayfish. It is a Missouri Species of Conservation Concern. Because of its small numbers and very limited range, within a single drainage system, the species could easily be extinguished from the face of the earth. Thus it is considered critically imperiled.

Life cycle

Like many other Ozark stream crayfish, this species apparently breeds in early fall, generating eggs and hatching young in the spring.

Human connections

In addition to feeding many types of wildlife, crayfish provide food for many species that humans hunt and fish. Crayfish are fascinating, colorful creatures in their own right, and part of our rich native heritage. Many people enjoy spying them through the clear water of Ozark streams.

Ecosystem connections

Crayfish are an important link in the food chain between plants and other animals, breaking down plant materials that are resistant to decay. Crayfish in turn are an important food for many other animals. Presence of crayfish in a stream or pond usually indicates good water quality.