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

crayfish Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some spe ...

which is native to the United States, in the

Ohio River The Ohio River () is a river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing in a southwesterly direction from Pittsburgh, Pennsylvania, to its river mouth, mouth on the Mississippi Riv ...

Basin in parts of

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

Kentucky Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...

, and

Indiana Indiana ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Michigan to the northwest, Michigan to the north and northeast, Ohio to the east, the Ohio River and Kentucky to the 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 The John Day River is a tributary of the Columbia River, approximately long, in northeastern Oregon in the United States. It is known as the Mah-Hah River by the Cayuse people. Undammed along its entire length, the river is the fourth longest ...

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

, which runs into the

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

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 The Animal Diversity Web (ADW) is a non-profit group that hosts an online database site that collects natural history, classification, species characteristics, conservation biology, and distribution information on species of animals. The website ...

. 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. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

Behavior

Many species of

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s that live in communities together utilize a

dominance hierarchy In the zoological field of ethology, a dominance hierarchy (formerly and colloquially called a pecking order) is a type of social hierarchy that arises when members of animal social animal, social groups interact, creating a ranking system. Dif ...

to establish order, and studies have shown that some species of

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

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 is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

in the

Northern United States The Northern United States, commonly referred to as the American North, the Northern States, or simply the North, is a geographical and historical region of the United States. History Early history Before the 19th century westward expansion, the ...

and parts of

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. 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, the Heartland or the American Midwest) is one of the four census regions defined by the United States Census Bureau. It occupies the northern central part of the United States. It ...

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 Freshwater crustaceans of North America Crustaceans described in 1852 Endemic crustaceans of the United States Taxobox binomials not recognized by IUCN Least concern biota of the United States Taxa named by Charles Frédéric Girard