A Species Alert has been issued for Crayfish plague (Aphanomyces astaci). It is unknown how the plague may have reached the infected sites but it can be been introduced through infected equipment or through introduction of a non-native crayfish species that can be a carrier of the plague.
Help tackle the threat from this plague by reporting any mass mortalities of the native White-clawed crayfish (Austropotamobius pallipes) or the presence of any non-native crayfish in our rivers and lakes. If you suspect you have seen a non-native crayfish, take a picture of it showing the underside of the claws and report it through this webpage https://records.biodiversityireland.ie/record/invasives or e-mail invasives@biodiversityireland.ie.
Below are some identification tips on how to tell the species apart. Note that males are larger than females and that body colouration can be very variable. You can also download the Crayfish identification tips handout.
White-clawed crayfish (Austropotamobius pallipes)
- Status: native protected crayfish and the only freshwater crayfish species found in Ireland.
- Length: adults up to 12 cm from the tip of tail to front of head but usually less than 10 cm.
- Body: topside may have a slightly wrinkled appearance, and normally a brown to olive colour. Underside pinkish-white.
- Claws: are noticeably granular and are whitish to light pink on the underside, never red.
- Most distinguishable feature from the non-natives: whitish underside of claws.
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Signal crayfish (Pacifastacus leniusculus)
- Status: potential invader with a risk of major impact.
- Length: adults up to 16 cm, but more often up to 15 cm.
- Body: topside is smooth, normally reddish-brown but can be bluish-brown. Claws seem very large relative to body size.
- Claws: white or turquoise patch at junction between fixed and moveable finger. Underside of claws are red.
- Most distinguishable feature from the White-clawed crayfish: red underside of claws.
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Red swamp crayfish (Procambarus clarkii)
- Status: potential invader with a risk of major impact.
- Length: adults up to 15 cm, but usually 10 cm.
- Body: roughened carapace, often red or maroon in colour. Some spines on carapace.
- Claws: large red tubercles and spines give the claws a knobbly appearance. Sharp carpal (wrist) spine.
- Most distinguishable feature from the White-clawed crayfish: knobbly claws with red tubercles
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Marbled crayfish (Procambarus species)
- Status: potential invader with a risk of major impact.
- Length: adults up to 13 cm, but usually less than 10 cm.
- Body: topside is smooth, bluish tinged to brightly blue with a marbled pattern.
- Claws: small claws and marbled the same as the body.
- Most distinguishable feature from the White-clawed crayfish: marbled pattern to body and claws.
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Turkish crayfish (Astacus leptodactylus)
Also known as the Narrow-clawed crayfish
- Status: potential invader with a risk of major impact.
- Length: adults up to 16 cm, but usually up to 15 cm.
- Body: topside is rough. Variable colour from sandy yellow to dark green, can be mottled in paler specimens, occasionally blue; leg joints often dark orange.
- Claws: claws normally same colour as body but underside lightly coloured. Fingers long, straight and narrow
- Most distinguishable feature from the White-clawed crayfish: fingers of claws are long, straight and narrow.
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Noble crayfish (Astacus astacus)
- Status: potential invader with a risk of major impact.
- Length: adults up to 17 cm, but usually not more than 15 cm.
- Body: mostly smooth. Topside colour very variable from light brown to dark brown, can be blue or red but normally dark brown to black at the back and olive-brown near the front.
- Claws: very broad. Topside of claws are granular and usually the same colour as the body. Underside of claws reddish to brown (but not bluish-white on top of claw as in Signal crayfish). Two widely spaced nodules (tubercles) on the inner side of the fixed finger.
- Most distinguishable feature from the White-clawed crayfish: Very broad claws and with two widely spaced nodules (tubercles) on the inner side of the fixed finger.
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Spiny-cheek crayfish (Orconectes limosus)
- Status: potential invader with a risk of major impact.
- Length: generally small, less than 10 cm but can reach 12 cm.
- Body: horizontal brown stripe on each abdominal segment is characteristic. Cheek spines may not be obvious until held. Note that Turkish crayfish may have small spines on cheeks and sides of head.
- Claws: Rather small, look granular (pitted) but feel smooth to touch. Has a large sharp spine on inside of ‘wrist’ (carpus). Underside tip of claws are orange with a black band below.
- Most distinguishable feature from the White-clawed crayfish: horizontal brown stripe on each abdominal segment.
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Additional identification resources
- Invasive Crayfish Species (Great Britain document) www.buglife.org.uk/sites/default/files/Invasive%20crayfish%20species%20-%20Profiles_0.pdf
- Protect Irish Crayfish leaflet
- Signal crayfish ID guide
- NAPRA Ireland risk assessments: http://nonnativespecies.ie/risk-assessments/
- Crayfish ID Tips handout
- Crayfish plague alert 2 updates: www.biodiversityireland.ie/crayfish-plaque-2017
There are many non-native species of crayfish available through the aquarium trade with just a selection shown here. If you see any species of crayfish that you think may be a non-native species please photograph and report it.