Note: The descriptions and illustrations come from many sources and authors (listed in the References below). Many of the descriptions are from authors describing crayfishes from other states, as well as my own observations of voucher specimens and new specimens from around PA (special thanks to John Rawlins of the Carnegie Institute and Ned Gilmore of the Academy of Natural Sciences for helping me obtain voucher specimens from their collections). I am solely responsible for the organization and scientific accuracy of this key...which, by the way, is likely to be updated as I see more species from around the state. Please do not publish any part of the key. While I believe it to be scientifically accurate, until published and reviewed by other crayfish biologists, it is for educational purposes only.
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Keystone species are those species that are most important in shaping the total ecology of a system. Crayfish are often keystone species in that they are an important resource for many other animals and can affect species diversity and abundance directly. The invading species, the Rusty Crayfish (Orconectes rusticus) can remove all plants from a system and eats fish eggs, too. This crayfish is very aggressive and removes local crayfish species (extirpates them), grows quickly (too big for fish to eat), and reaches high densities. Water systems dramatically change when the rusty crayfish moves in and takes over.
Birds (herons, barred owls, other water birds), water snakes, large salamanders, frogs, raccoons, muskrats, minks, river otters, many fish (trout, bass, etc.), turtles, other crayfish, and people (Cajun crawfish!). Crayfishes represent high-quality protein that nearly any animal will want to eat. The shell (carapace) of a crayfish, however, is not digestible by animals (although the calcium may be removed) and is typically broken down by microbes.
Insects, plants, detritus (decomposing plants and animals), worms, other crayfishes, fish eggs (especially the invading Rusty Crayfish...very bad for the streams ecology), etc. Crayfishes are basically omnivores...they'll eat anything, but prefer high protein content in their food.
Good question! So far there are 12 species (13 if you include subspecies) of crayfishes reported in PA. Sometimes they are easy to tell apart, others are very hard to distinguish. I suspect a few more species will be found since they are found in neighboring states. Two species are introduced to the state, the rusty crayfish and the northern crayfish (Orconectes virilis). To determine what species a crayfish is, go to the Key to PA Crayfishes.
Some crayfishes are burrowers and can live far from surface water. They must have underground water, though, like a shallow aquifer, underground spring, or nearby water. Burrows can be quite deep with many branching tunnels, some leading to nearby water. If you live in the right places (southwestern and eastern PA), you might see crayfishes walking around a garden far from water during the humid summer nights.
Crayfishes can be nearly any natural color: yellow, green, blue, red, white (cave species), and every possible combination of colors. They can have intricate patterns of color, solid colors with different colored edges, spotted, and multiple colors at once. Oddly, burrowing crayfish that are rarely or never seen in open water can be the most colorful. Species found in open water are generally the color of the rocks, sand, mud, grass, etc. of the background substrate so that predators can't see them. I have found brick-red crayfish in streams with leaf litter of the same color, and greenish crayfish (same species as the brick-red crayfish) in rocky steams. Natural selection will determine which color is best for survival.
Crocker, D.W. 1957. The Crayfishes of New York State. SUNY at Albany. Albany, NY.
Crocker, D.W. and D.W. Barr. 1968. Crayfishes of Ontario. University of Toronto Press, Canada.
Hobbs, Jr., H.H. 1972. Crayfishes (Astacidae) of North and Middle America. US Government Printing Office, Washington, D.C.
Jezerinac, R.F., G.W. Stocker, and D.C. Tarter. 1995. The Crayfishes (Decapoda: Cambaridae) of West Virginia. Ohio Biological Survey, Ohio State Unversity, Columbus, Ohio.
Ortmann, A.E. 1906. The Crawfishes of the State of Pennsylvania. Memoirs of the Carnegie Museum, Vol. II, No. 10., Pittsburgh, PA.
Page, L.M. 1985. The Crayfishes and Shrimps (Decapoda) of Illinois. Illinois Natural History Survey Bulletin, Vol. 33, Article 4, Sept.
Peckarsky, B.L., P.F. Fraissinet, M.A. Penton, and D.J. Conklin, Jr. 1990. Freshwater Macroinvertebrates of Northeastern North America. Cornell University Press, Ithaca, NY.
Pflieger, W.L. 1996. The Crayfishes of Missouri. Missouri Dept. of Conservation, Jefferson City, MO.
Taylor, C.A. et al. 1996. Conservation Status of Crayfishes of the United States and Canada. Fisheries, Vol. 21, No. 4:25-38.