Allegheny Crayfish, Faxonius obscurus

OTHER COMMON NAMES

Obscure crayfish

ETYMOLOGY

Faxonius, named for Walter Faxon (1848-1920), American ornithologist and carcinologist. Former genus, Orconectes, is from Orcus, god of the underworld in Roman mythology + nectes: swimming (Greek); obscurus: covered (Greek), perhaps for its propensity to hide under rocks

Ecology, Habitat, & Behavior

While Allegheny crayfish are listed as being present in Vermont, we’re on the very outer edge of their range and they are certainly not common here. If you were to seek them out, you’d likely have the most luck in the rocky bottomed sections of secondary and tertiary streams where fish predators are less abundant (source). While the natural history of crayfish in general is understudied, this species in particularly has remained out of the lens of scientists and there is sparse information on their habits (the two best resources were from 1957 and 1972).

In an exhaustive study of the life history of the Allegheny crayfish (along with the closely related northern clearwater crayfish and Sanborn’s crayfish), Dorothy Fielder revealed several interesting patterns in crayfish population dynamics. Not surprisingly, abundance was the smallest in the late fall and early spring, with post-breeding and winter mortality the prime driver of declining populations. By May virtually all male Allegheny crayfish were second form (F2) non-breeding males, which was earlier than the other 2 related species. About 2 months later, in early July, males began to revert to their second form (F2) just in advance of the breeding season. In April, when the females are in berry, they become almost entirely absent from trapping efforts.

Allegheny crayfish are smaller crayfish, lower on the dominance hierarchies when living in the same place as other species of crayfish. They establish hierarchies within a population, with larger, more aggressive individuals gaining access to preferred refugia (hiding places) and feeding spots. While dominant individuals may have the advantage in acquiring resources (Allegheny crayfish greatly prefer detritus over animal or green plant food sources: source), and therefore able to put more energy towards molting and growth, in periods where food was not a limiting resource (usually in the summer), smaller individuals molted more frequently and grew quicker than larger ones (source).

QUICK FACTS

Avg carapace length: <1.5 inchesLife expectancy: 2-4 yearsAge at maturity: Males in 2nd summerHabitat: Slow moving water with rocky substrate# of eggs: 75+Diet: Primarily detritus, though mostly unknownNative or non-native: Non-nativeActivity pattern:

Diurnal and Nocturnal

Uses: Bait

Life History Event Date/Season
Mating August to September
Fertilization Delayed
Laying Eggs April & May
Young detach from female June
Males in F1 Late summer
Males in F2 Spring

Key features for ID + similar species

Overall, extremely similar to the closely related northern clearwater crayfish.

  1. Dark brown wedge on abdomen
  2. Lacks median carina (keel) on rostrum
ROSTRUM

Wide, dished rostrum with straight, tapering margins. Absence of a median carina can differentiate this species from the northern clearwater crayfish.

COLOR/MARKINGS

Light brown to olive green body, with dark brown wedge on abdomen.

CHELAE

Large and straight. Palm with two rows of tubercles on mesial (towards the center of the crayfish) margin. Fingers somewhat long, with dactyls straight, hooked inward at tip.

AREOLA

Wide areola (the gap between the carapace plates).

Range map for Allegheny Crayfish

Range map based on observations from iNaturalist.org

As of 2019, it does not have any data points on iNaturalist, but it is found in the state. Range map based on observations from iNaturalist.org

General Research on Crayfish

  • NOBANIS: Invasive Alien Species Fact Sheet : source
  • Crayfish of the White River Watershed: source
  • Crayfish curriculum for educators: source
  • The Crayfishes of New England: source
  • Species of Ontario Crayfish: source
  • Lecture on Crayfish: video
  • Some aspects of the life histories of three closely related crayfish species, Orconectes obscurusO. sanborni, and O. propinquussource
  • Dictionary of crayfish names: source
  • Biological synopsis of the rusty crayfish: source
  • Observations on the life cycle of Procambarus acutus acutus in South Carolina culture ponds: source
  • Natural History of the two Crayfish of Northwestern Iowa, Orconectes virilis and Orconectes immunis: source

Crayfish of Vermont species profiles