The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Faxonius obscurus
Faxonius obscurus
(Allegheny crayfish)
Native Transplant

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Faxonius obscurus (Hagen, 1870)

Common name: Allegheny crayfish

Synonyms and Other Names: Orconectes obscurus (Hagen, 1870). This species underwent a reclassification in 2017, changing the genus of non-cave dwelling Orconectes to Faxonius (Crandall and De Grave 2017).

Taxonomy: available through www.itis.govITIS logo

Identification: The Allegheny Crayfish, Faxonius obscurus, displays a light brown to olive-green coloration, and a dark brown wedge on the dorsal surface of the abdomen (Ortmann 1906; Taylor et al. 2015). This species coloration is similar to the Northern Clearwater Crayfish (Faxonius propinquus), which commonly cooccurs with F. obscurus. The coloration of F. propinquus claw tips are generally orangish-brown followed by a pale or yellowish band of color. This differs from F. obscurus claws that are usually tipped with orangish-brown, followed by a dark green-blackish band, and then a pale-yellow band. Adults of the two species may be distinguished by their coloration if they have recently molted; however, algae growth and weathering of the shells may inhibit this, requiring further examination of morphological features (Ortmann 1906; Taylor et al. 2015).

Faxonius obscurus can be distinguished by examining several morphological traits, which are well depicted in Taylor et al. (2015). They possess a concave rostrum that lacks a median keel, and first form males have a prominent shoulder on the anterior margin of their gonopod elements. Its chelae (pincers) are large and straight with moderately long fingers and two rows of tubercles along the mesial margin of its palm region (Ortmann 1906; Crocker 1957; Taylor et al. 2015). Chelae of old males are broader and more flattened with a wide gap at the base (Ortmann 1906).

Size: Individuals from the Mahoning River, Portage County, Ohio were found to have a maximum CL of 40 millimeters (mm) (Fielder 1972). The largest specimen identified by Ortmann (1906) from Allegheny County, Pennsylvania, measured a total length (TL) of 93 mm.

Native Range: The Allegheny Crayfish is native to streams of the Allegheny, Monongahela, Genesee, and the upper Ohio River Drainage; as well as a small portion of the upper Lake Erie Drainage. Its native distribution lies within eastern Ohio (Jezerinac 1986; Taylor et al. 2015), western Pennsylvania (Ortmann 1906; Bouchard et al. 2007), a small portion of west Maryland (Kilian et al. 2010), northern West Virginia (Loughman and Welsh 2010), and western New York (Crocker 1957).

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Faxonius obscurus are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
ME200320032Lower Androscoggin River; Presumpscot
MD198219821Lower Susquehanna
NY193920197Irondequoit-Ninemile; Lake Ontario; Lower Hudson; Mohawk; Niagara River; Oneida; Schoharie
PA1982202312Bald Eagle; Conococheague-Opequon; Lehigh; Lower Susquehanna; Lower Susquehanna-Penns; Lower Susquehanna-Swatara; Lower West Branch Susquehanna; Mid Atlantic Region; Raystown; Schuylkill; Upper Juniata; Upper Susquehanna-Lackawanna
VA201920191North Fork Shenandoah

Table last updated 5/21/2024

† Populations may not be currently present.

Ecology: The Allegheny crayfish inhabits large streams with firm substrates such as sand, gravel, and cobble (Ortmann 1906; Crocker 1979; Taylor et al. 2015). Specimens are generally found under stones or large debris in stream beds where they excavate small holes. They rarely dig sizable burrows; however, when larger stones are not present they will dig shallow tunnels just below the surface along the water’s edge. The openings of these tunnels are often inconspicuous, and they tend to run horizontally for only a few inches (Ortmann 1906).

The life history of the Allegheny Crayfish is similar to that of other Faxonius species from the region. Mature F. obscurus mate during August and September, and their eggs hatch the next spring between April and May. Once hatched, the young become independent after one to two months of development. During their first summer, immature individuals molt several times, increasing their carapace length by 1 to 2 or more mm each time. Their growth and activity ceases during the winter months and continues as temperatures rise during the spring. Male F. obscurus reach maturity during their second summer, and once mature they transition to their second form in the spring and revert to first form in late summer (Fielder 1972). The minimal carapace length (CL) of sexually mature individuals was estimated to be 19.9 mm for males and 23.1 mm for females (Crocker 1957). The maximum life expectancy of F. obscurus is believed to be roughly 2 years (Fielder 1972).

Means of Introduction: This species was likely introduced outside of its native range through bait bucket releases (Ortmann 1906; Berrill 1978; Bouchard et al. 2007).

Status: This species has been introduced to and is established regionally in Massachusetts, Maine, eastern Pennsylvania, eastern New York, and Ontario, Canada (Crocker and Barr 1968; Berrill 1978; Crocker 1979; Jezerinac 1986; Bouchard et al. 2007). F. obscurus is numerous within Delaware River Drainage and has been collected from both Pennsylvania and New Jersey (Bouchard et al. 2007).

Impact of Introduction: Invasive Faxonius species are known to threaten native crayfish species through competitive exclusion or hybridization (Lodge 2000; Loughman and Welsh 2010).

Remarks: F. obscurus has been displaced from parts of its native range, and it is threatened by the Rusty Crayfish (Faxonius rusticus) and Virile Crayfish (Faxonius virilis) (Jezerinac 1986; Daniels 1998; Kilian et al. 2010; Taylor et al. 2015).

References: (click for full references)

Berrill, M. 1978. Distribution and ecology of crayfish in the Kawartha Lakes region of southern Ontario. Canadian Journal of Zoology 56:166-177.

Bouchard, R.W., D.A. Lieb, R.F. Carline, T.R. Nuttall, C.B. Wengert, and J.R. Wallace. 2007. 101 Years of Change (1906 to 2007) The Distribution of the Crayfishes of Pennsylvania Part I: Eastern Pennsylvania. Academy of Natural Sciences of Philadelphia, Philadelphia, PA.

Crandall, K.A. and S. De Grave. 2017. An updated classification of the freshwater crayfishes (Decapoda: Astacidea) of the world, with a complete species list. Journal of Crustacean Biology 37(5):615-653. https://doi.org/10.1093/jcbiol/rux070

Crocker, D.W. 1957. The crayfishes of New York State (Decapoda, Astacidae). University of the State of New York, Albany, NY.

Crocker, D.W., and D.W. Barr. 1968. Handbook of the crayfishes of Ontario. University of Toronto Press, Toronto, Ontario.

Crocker, D.W. 1979. The crayfishes of New England. Proceedings of the Biological Society of Washington 92:225-252.

Daniels, R.A. 1998. Changes in the distribution of stream-dwelling crayfishes in the Schoharie Creek system, eastern New York State. Northeastern Naturalist 5:231-248. https://www.jstor.org/stable/3858623

Fielder, D.D. 1972. Some aspects of the life histories of three closely related crayfish species, Orconectes obscurus, O. sanborni, and O. propinquus. The Ohio Journal of Science 72(3):129-145. http://hdl.handle.net/1811/5691

Jezerinac, R.F. 1986. Endangered and threatened crayfishes (Decapoda: Cambaridae) of Ohio. Ohio Journal of Science 86(4):177-180. http://hdl.handle.net/1811/23156

Kilian, J.V., A.J. Becker, S.A. Stranko, M. Ashton, R.J. Klauda, J. Gerber, and M. Hurd. 2010. The status and distribution of Maryland crayfishes. Southeastern Naturalist 9(Special Issue 3):11-32.

Lodge, D.M, C.A. Taylor, D.M. Holdich, and J. Skurdal. 2000. Nonidigenous crayfishes threaten North American freshwater biodiversity: lessons from Europe. Fisheries 25(8):7-19. https://www.researchgate.net/publication/250017393

Loughman, Z. J., and S.A. Welsh. 2010. Distribution and conservation standing of West Virginia crayfishes. Southeastern Naturalist 9(3):63-78. https://www.researchgate.net/publication/232689227

Ortmann, A.E. 1906. The crawfishes of western Pennsylvania. The Annals of the Carnegie Museum 3:387-406.

Taylor, C.A., G.A. Schuster, and D.B. Wylie. 2015. Field guide to crayfishes of the Midwest. Illinois Natural History Survey, Champaign, IL.

Author: Procopio, J.

Revision Date: 5/10/2019

Citation Information:
Procopio, J., 2024, Faxonius obscurus (Hagen, 1870): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=2243, Revision Date: 5/10/2019, Access Date: 5/21/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


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Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [5/21/2024].

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