The rusty crayfish (''Faxonius rusticus'') is a large, aggressive species of freshwater

crayfish Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mu ...

which is native to the United States, in the

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Basin in parts of

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia to ...

, and

Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...

. Its range is rapidly expanding across much of eastern North America, displacing native crayfishes in the process. The rusty crayfish was first captured in Illinois in 1973, and has been collected at over 20 locations in the northern portion of the state. In 2005, ''F. rusticus'' was found for the first time west of the

Continental Divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...

, in the John Day River,

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, which runs into the

Columbia River The Columbia River (Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, C ...

Description

Adult rusty crayfish can reach 10 centimeters (4 inches) in length, although they reach maturity at about 4.4 cm (1.7 in),Pappas, Janice
''Orconectes rusticus''
Animal Diversity Web. and can range in color from greenish grey, to reddish brown, They can be easily recognized by two "rusty", reddish colored spots on the sides of their back and their large front claws with black bands around the tips.Jensen, Doug (26 July 2013)
"Rusty Crayfish"
Minnesota Sea Grant. Male rusty crayfish have small hook-like features on their first pair of hind legs that they use to hold onto a female while mating.Gunderson, Jeffrey

Rusty Crayfish Gender Identification. File:Faxonius rusticus-male ventral.jpg, Male in

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...

Behavior

Many species of

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s that live in communities together utilize a dominance hierarchy to establish order, and studies have shown that some species of

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s do as well. The dominance hierarchy is an important aspect of a crayfish's biology and behavior. Crayfish tend to form dominance hierarchies with the other members of their population in a particular environment. The largest male will generally demonstrate the most dominance over the others by being the most aggressive, and picking fights with the other, smaller crayfish. The crayfish that wins the most fights is placed at the top of the hierarchy with the other members generally ranking in descending order based on size and sex. Studies have suggested that the largest determining factor in the formation of dominance hierarchies is size rather than sex. That means that female rusty crayfish can rank higher in the dominance hierarchy than male rusty crayfish if they are larger than them.

As an invasive species

The larger size and aggressive nature of rusty crayfish that have been introduced to a body of water makes it harder for them to be preyed upon by native species of fish, which are not accustomed to crayfish fighting them back. Instead of running away like the native crayfish species do when they come in contact with a predator, the rusty crayfish will take an attack stance with its claws raised above its head, which will generally scare away most predatory fish. Additionally, adult rusty crayfish can be too large for some fish to consume."Wisconsin Aquatic Invasive Species."
wisc.edu Because the rusty crayfish are able to avoid predators fairly well, their population in these new aquatic ecosystems was able to grow extremely quickly and within twenty years the rusty crayfish population had exploded and become an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

in the

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and parts of

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. Because these rusty crayfish populations have basically taken over the natives species' habitats and forced them out of their homes, many populations of native crayfish have experienced drastic decline over the past fifty years and the rusty crayfish has become the dominant species in much of the

Midwestern United States The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of the United States. I ...

Control efforts

There are some chemicals that will selectively kill only crayfish that have not been registered or labeled for crayfish control, but kill all species of crayfish and are not specific to rusty crayfish."Rusty Crayfish."
in.gov. Manual harvest for human consumption is an effective control strategy due to the large size of rusty crayfish. However, this strategy is only useful in reducing the adult population. Once a population of rusty crayfish is introduced to a body of water, it is very difficult to completely eradicate them. Therefore, the best control strategy is to try to prevent any further spread of the rusty crayfish. The best ways to prevent invasive species spread is to learn to identify the invasive species, and not use the species as bait or transport the species to bodies of water where it is not already present.

References

{{Taxonbar, from1=Q59712751, from2=Q3933598 Cambaridae Fauna of the United States Freshwater crustaceans of North America Crustaceans described in 1852