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      Juvenile Orconectes virilis crayfish (Photo: Crustaceanguy, - Click for full size
    Taxonomic name: Orconectes virilis (Hagen, 1870)
    Common names: northern crayfish (English), virile crayfish (English)
    Organism type: crustacean
    Orconectes virilis is a crayfish native to the Missouri, Mississippi, Ohio, and Great Lakes drainages of the United States. It has become introduced to locations throughout the United States through live pet and bait trade and has also established in a few locations in Europe. Its important impacts to introduced systems include competition with and displacement of native fish and crayfish and the reduction of snail, macroinvertebrate, and macrophyte abundance and biodiversity.
    Orconectes virilis is reddish-brown to olive-brown in color. Adults reach about 13 cm long with males typically growing larger than females. It has bumps on the medial side of its carapace and along its chelae. Chelae also often have dark specs and orange or reddish tips. O. virilis may also have paired black marks along its abdomen (ANSIS, 2007).
    Similar Species
    Astacidea, Orconectes immunis, Orconectes limosus, Orconectes punctimanus

    Occurs in:
    lakes, water courses, wetlands
    Habitat description
    Orconectes virilis may inhabit rivers, streams, lakes, marshes and ponds that are permanent and well oxygenated (Collicut, 1998). They prefer warm waters of moderate turbidity with cobble or rocky substrates and abundant logs, rocks, vegetation, and other debris to use as cover. They are also known to dig pits in river banks and under rocks when water levels are low (ANSIS, 2007; Benson, 2010). O. virilis can survive a temperature range of 0-32°C and has a preferred temperature range of 24-25°C. Its movement is halted at temperatures below 10°C. It is unable to withstand acidic conditions and prefer locations with a pH of over 5.37. O. virilis is also untolerant of poor water quality and high salinity (ANSIS, 2007).
    General impacts
    Orconectes virilis may have a variety of impacts on introduced ecosystems that include direct and indirect impacts on habitat, competition with and displacement of native species, and other ecological interactions.

    O. virilis is known to alter and reduce macrophyte biomass and diversity (Chambers et al, 1990; Davidson et al, 2010; Olden et al, 2009). It may displace native crayfish as in the case of the endangered Pacifastacus nigrescens in California (Light et al, 1995); Orconectes obscurus and Cambarus bartonii in North Carolina (Cooper et al, 1998); and Orconectes limosus and Cambarus bartonii bartonii in Maryland (USA) (Schwartz et al, 1963). Field and laboratoy observations indicate that is may compete with and/or cause the decline of native fish species such as juvenile desert suckers (Catostomus clarkii), the Sonora sucker (Catostomus insignis), and the federally threatened Little Colorado spinedace (Lepidomeda vittata) in Arizona (Davidson et al, 2010; Bryan et al, 2002); the flannelmouth sucker (Catostomus latipinnis) in Colorado (Carpenter, 2005); and the White Sands pupfish (Cyprinodon tularosa) in New Mexico (Rogowski & Stockwell, 2006). It has been reported to contribute to the decline of the Chiricahua leopard frog (Rana chiricahuensis) in Arizona (Davidson et al, 2010). O. virilis is also known to cause the decline of native snails (ANSIS, 2007), as in the case of three forks spring snail (Pyrgulopsis trivialis) in Arizona (Davidson et al, 2010) and Canadian native snails Stagnicola elodes and Physa gyrina in laboratory studies (Hanson et al, 1990).

    Additional impacts associated with O. virilis include the reduction of insects and other macroinvertebrates (Davidson et al, 2010; Hanson et al, 1990), the alteration of the structure and composition of littoral zones (Chambers et al, 1990), the increase in turbidity of waters (Davidson et al, 2010), and impacts to irrigation networks and levees as a result of their burrowing near head gates and weir boxes (Godfrey, 2002).

    Orconectes virilis is a popularly consumed food in the United States and increasingly more so in Europe (Collicut, undated). O. virilis a commonly used fish bait and is sold as such in bait shops. It is also sold commercially in the pet trade as pets or prey for predaceous aquarium fishes (Hunner, 1997). Beginning in approximately 1950 O, virilis was stocked as a biological control in the Colorado River watershed of western New Mexico and northeastern Arizona, primarily for vegetation control (Johnson, 1986).
    Geographical range
    Native range: United States (USA): Arkansas, Colorado, Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Montana, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, Texas, Wisconsin, Wyoming; Canada: Manitoba, Ontario, Saskatchewan
    Known introduced range: United States (USA): Alabama, Arizona, California, Connecticut, Delaware, Idaho, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Pennsylvania, Rhode Island, Tennessee, Utah, Vermont, Virginia, West Virginia; Canada: New Brunswick; Mexico: Chihuahua; Netherlands, Sweden, United Kingdom (UK)
    Introduction pathways to new locations
    Live food trade:
    Other: Orconectes virilis is commonly used as fishing bait and commonly sold in bait shops. Many of their introductions have been attributed to their use as such.
    Pet/aquarium trade: Orconectes virilis may be introduced to new locations via aquarium trade (Filipova et al 2009).

    Local dispersal methods
    Other (local): Orconectes virilis is used as fishing bait
    Water currents:
    Management information
    Preventative measures: Education of the public, especially, pet traders, anglers, and bait shop owners, of the negative impacts of Orconectes virilis and the dangers associated with releasing nonnative crayfish may help reduce their introductions to new locations (ANSIS, 2007).
    To minimize effects to irrigation systems in rice fields, the fields may be drained temporarily to drive crayfish in to their burrows so rice seedlings may establish (Godfrey, 2002).

    Biological control: The protection of sport fish and regulations that reduce their harvest in order to increase predation on Orconectes virilis is one potential means of reducing its populations (ANSIS, 2007).
    A bacteria and the White Spot Syndrome Virus were examined for their effectiveness as potential biological controls for Orconectes virilis. The bacteria Spiroplama penaeiled led to 100% mortality when injected but body parts injected with S. penaeiled and fed to O. virilis did not induce mortality indicating that transmission via cannibalistic feeding is not viable. The White Spot Syndrome Virus yielded 100% mortality when injected or fed to all sizes of O. virilis indicating that it may be spread through cannibalistic feeding. WSSV did not infect non-target invertebrates but further research into this virus as well as other potential biological control agents for O. virilis is required before a viable one is found (Davidson et al, 2010).

    Orconectes virilis is omnivorous and consumes a variety of live and dead animal and plant material (ANSIS, 2007). It is known to consume macroinvertebrates such as snails and insects, as well as, small fish, fish eggs, tadpoles, and macrophytes. O. virilis is believed to obtain most of its nutrition by scavenging dead animals (Collicut, 1998).
    Breeding of Orconectes virilis begins in the fall to early spring and extends until the adults retreat to deep water and become inactive. Breeding sometimes occurs for a brief period in the spring when the water begins warming (Collicut, 1998; ANSIS, 2007). Females store sperm for up to months and fertilize their eggs in the spring. Eggs are attached to swimmerets in a large ball resembling a raspberry. The eggs hatch one to two months after they are laid. Young hatchlings look like miniature adults and can probably grow to about 2-3cm long by the fall. (Collicut, 1998).
    Lifecycle stages
    The maximum lifespan of Orconectes virilis is 3 years. They undergo several molts in their first few months. O. virilis typically reaches a length of 23-56 mm in first year and a length of 58-84 mm by the second. They reach maturity during their second summer usually around 24mm.(ANSIS, 2007). O. virilis undergoes form alternation between the sexually mature Form I during the mating season and the sexually immature Form II outside of the mating season (Matthews et al, 2008).
    Reviewed by: Dr. Brian Hazlett. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor. USA
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Wednesday, 21 July 2010

ISSG Landcare Research NBII IUCN University of Auckland