Orconectes virilis



Legal status

Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).

Regulated invasive species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].


Invasive species - risk of High Impact

Irish status


Introduction pathways - 1

Escape from Confinement

Introduction pathways subclass - 1

Pet/aquarium species

Invasive score


NAPRA Ireland risk assessed


Species Biology


Up to 12cm crayfish with a smooth carapace coloured chestnut or chocolate brown with a wine glass shaped light brown pattern (Holdich & Sibley 2009). Claws are broad and flattened with prominent pale coloured bumps (tubercles) on the margins. They are the same colour as the body but are an off-white colour underneath (Holdich & Sibley, 2009). The claws often have a blueish tint and are larger in the males (Collicut, 1998).


Orconectes virilis is an 'opportunistic omnivore' eating plant material, snails, insects, fish, fish eggs, tadpoles, macrophytes and carrion (Collicut, 1998). They are tolerant of a wide range of conditions (CABI, 2012) and are most active at night (Collicut, 1998).

May compete with Ireland's native White-clawed crayfish (Austropotamobius pallipes) monopolizing resources (Rogers & Watson, 2013) and can alter river ecosystems by reducing the numbers of aquatic macrophytes and macro invertebrates (Rogers & Watson, 2013). This species digs burrows and uses rocks and gravel for cover (CABI, 2102). Burrowing activities can destabilize river/lake banks leading to erosion and increasing water turbidity (CABI, 2012).

A combination of high fecundity, rapid growth and early sexual maturity means large populations can develop rapidly (Holdich & Sibley, 2009) and this omnivore may outcompete the native white-clawed crayfish (A. pallipes) for resources. They are probable vectors for Crayfish plague (Aphanomyces astaci) (Holdich & Sibley, 2009; Rogers & Watson, 2013) which can decimate native crayfish populations.

May be predated by coots (Fulica atra), herons (Ardea cinerea), perch (Perca fluviatilis), pike (Esox lucius), otter (Lutra lutra), mink (Mustela vison) and eels (Anguilla anguilla) as may O. limosus (Holdich & Black, 2007).


Mating occurs in autumn or spring. The female can store sperm once mated in autumn and will fertilise the eggs in spring (Collicut, 1998). Females can produce up to 490 eggs (Rogers and Watson, 2013). The fertilised eggs are carried attached to the female's abdomen until the young hatch in April/May (CABI, 2012). Hatchlings are small versions of the adult crayfish and will moult their shells as they grow. Both sexes become sexually mature at approximately 1 year of age (CABI, 2012). Males and females display cyclic dimorphism alternating between Form I (sexually active form) during the mating season and Form II (non-breeding form) once the mating season is over (Holdich & Sibley, 2009).

Pathway and vector description

The nearest population to Ireland is in the UK where they are thought to have been introduced by the dumping of an aquarium contents (Ahern et al., 2008; Holdich and Sibley, 2009). From there they spread along waterways and even over short distances on land. They can disperse up to 2km per year (Ahern et al., 2008). As the females can store sperm it is possible for single female could start a new population even if she isn't carrying any eggs (CABI, 2012).

Mechanism of impact

Competition, Disease transmission, Grazing/Herbivory/Browsing

Management approach

There are no effective methods for control or eradication of crayfish at present (NNSS, 2011).


Currently trapping is most used but juveniles don't often enter the traps and the adults are very wary making them difficult to trap (Holdich & Black, 2006).


Biocides can be used but they are expensive and cannot be used in flowing water (NNSS, 2011).

Broad environment


Habitat description

Freshwater rivers, lakes, canals, ponds, waterfilled gravel pits, streams and wetlands. Requires rocks or logs or vegetation to hide from predators during daytime (Collicut, 1998).

Species group


Native region

North America

Similar species

Austropotamobius papilles (White-clawed crayfish). A. papilles is brown to olive coloured, sometimes blueish and lacks tubercles on the claws.


World distribution(GBIF)

Introduced in Europe to the Netherlands and the United Kingdom (Ahern et al., 2008; Holdich & Sibley, 2009).

Native distribution

Native to North America (Missouri, Mississippi, Ohio and the Great Lakes Drainage system) and Canada.

Temporal change

Records submitted to Data Centre in 2021

The following map is interactive. If you would prefer to view it full screen then click here.

How can you help

Report any sightings to the National Biodiversity Data Centre.



Ahern D., England J. and Ellis A. (2008). The virile crayfish, Orconectes virilis (Hagen, 1870)(Crustacea: Decapoda: Cambaridae), identified in the UK. Aquatic Invasions 3(1):102 -104. Site accessed 10 October 2017.

Buglife (undated) Crayfish identification, distribution and legislation. Leaflet produced for Buglife and the Environment Agency. Buglife, Plymouth Site accessed 9 October 2017.

Collicut, D. 1998. Biology of Northern Crayfish. Nature North. Site accessed 10 October 2017.

CABI. (2012). Orconectes virilis (Virile caryfish) [original text by Adam Ellis] [Online]. Invasive Species Compendium: Wallingford, UK: CAB International. Available: Accessed 10 October 2017.

European Commission. (2017). Invasive Alien Species of Union Concern. European Union, Luxembourg.Global Invasive Species Database (GISD) 2015. Species profile Orconectes virilis. Available from: Site accessed 10 October 2017.

Holdich, D & Black, J (2006) The spiny-cheek crayfish, Orconectes limosus (Rafinesque, 1817) [Crustacea: Decapoda: Cambaridae], digs into the UK. Aquatic Invasions 2 (1) pp. 1-15, Site accessed 6 October 2017.

Holdich D.M. & Sibley P.J. (2009) ICS and NICS in Britain in the 2000s; Brickland J, Holdich DM and Imhoff EM (eds) (2009). Crayfish conservation in the British Isles. Proceedings of a conference held on 25th March 2009 in Leeds, UK. Site accessed 9 October 2017

Non-native Species Secretariat (NNSS) (2011) Rick assessment for Orconectes limosus – Spiny-cheek crayfish. Risk assessment carried out for Great Britain. Site accessed 6 October 2017.

Rogers, D. and Watson, E. (2013). GB Non-native Organism Risk Assessment for Orconectes virilis. Site accessed 10 October 2017.

GISD Species Account

UK Crayfish Hub