Pacifastacus leniusculus Dana, 1852

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English Signal crayfish Status LU: established. 1st record: 1996.
Lëtzebuergesch Signalkriibs Status Eur.: established. IAS of EU concern.
Français Écrevisse de Californie RA: ISEIA: A3, Black List. Harmonia+: n/a.
Deutsch Signalkrebs Wikipedia: Wikipedia - English - Signal crayfish Wikipedia - Français - Ecrevisse de Californie Wikipedia - Deutsch - Signalkrebs Nederlands | Wikispecies: n/a (2020)
Nederlands Signaalkreeft Back to the list of invertebrates

Report the species

Report Pacifastacus leniusculus to the National Museum of Natural History.

Brief description

Signal crayfish female Pacifastacus leniusculus Pacifastacus leniusculus Dana, 1852 is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the North European Astacus astacus fisheries, which were being damaged by crayfish plague, but the imports turned out to be a carrier of that disease. The signal crayfish is now considered an invasive species across Europe, Japan, and California ousting native species there. The signal crayfish is now the most widespread alien crayfish in Europe, occurring in 25 countries. From 1907, crayfish plague, an infectious disease caused by the water mould Aphanomyces astaci, damaged stocks of the native European crayfish Astacus astacus. All American species carry the infection, but it is only lethal to individuals that are already stressed; to European species, the infection is rapidly fatal (Wikipedia contributors 2020).

The signal crayfish is an omnivore, with most of its dietary intake being detritus. Members of this species are typically 6–9 centimetres long, although sizes up to 16–20.32 centimetres are possible. They are bluish-brown to reddish-brown in colour, with robust, large, smooth claws. They have a white to pale blue-green patch near the claw hinge, like the white flags that signalmen used for directing trains—hence the name. Around 200–400 eggs are laid after mating in the autumn, and are carried under the female’s tail until they are ready to hatch the following spring. The eggs hatch into juveniles, which pass through three stages (two moults) before leaving their mother. Sexual maturity is reached after two to three years, and the lifespan can be up to 20 years (Wikipedia contributors 2020).

Status and distribution in Luxembourg

Records of Pacifastacus leniusculus Dana 1852 in Luxembourg. Data source: Recorder-Lux, iNaturalist & GBIF, 2024-07-13.

1020 occurrences of Pacifastacus leniusculus Dana, 1852 are documented in the Recorder-Lux database, the first from 1996 (MNHNL, iNaturalist & GBIF, 2020). The species has been present in Luxembourg since much earlier though. Dhur & Massard (1995) describe stockings of P. leniusculus in the lake of Esch/Sûre (1972), Kriibseweier/Gonderange (1974, 1975, 1976), Attert, Wark, Tandlerbaach, Dirbach, ponds at Kockelscheuer and Gostingen, the lake in Echternach, the Sûre close to Wallendorf and the Syre, ranging from 1977 to 1986.


Action plan

Finalised Action Plan for Pacifastacus leniusculus (De Sousa 2020)

Risk assessment

ISEIA protocol

A3 (3+3+3+2) = Black List (Ries et al. 2017: 68).

Harmonia+ protocol

Not assessed yet.

Worldwide distribution

Fact sheet

PDF fact sheet of the Nature and Forestry Administration: FR | DE


  • Administration des eaux et forêts, Service de la chasse et de la pêche, 1998. Fische in Luxemburg. Kartierung der Fische, Neunaugen und Flußkrebse des Großherzogtums Luxemburg. ISBN 2-495-28004-8. 153 pp.
  • Administration de la gestion de l’eau, 2010. Les poissons au Luxembourg, Cartographie des poissons, lamproies et écrevisses du grand-duché de Luxembourg. 2e édition. ISBN 978-2-91989-713-1. 213 pp.
  • Atten, D., 1987. Étude des populations d’Ecrevisses d’eau douce au grand-duché de Luxembourg et spécialement de l’Écrevisse de Californie. Luxembourg, Mémoire sci. asp. prof., 190 pp.
  • De Sousa, Tiago, 2020. Plan d’action pour espèces exotiques envahissantes au Grand-Duché de Luxembourg: l’Écrevisse signal, Pacifastacus leniusculus (Dana, 1852) et l’Écrevisse américaine, Faxonius limosus (Rafinesque, 1817). Version 4/09/2020. Administration de la nature et des forêts, Luxembourg. 29 pp.
  • Dhur, G. & J.A. Massard, 1995. Étude historique et faunistique des Invertébrés immigrés ou introduits dans la Moselle luxembourgeoise et ses affluents. Bull. Soc. Nat. luxemb. 96: 127-156. [PDF 1896 KB]
  • GBIF, 2020. Pacifastacus leniusculus (Dana, 1852) in GBIF Secretariat (2019). GBIF Backbone Taxonomy. Checklist dataset [accessed 2020-03-13]
  • Meisch, C. & J.A. Massard, 2015. Les recherches sur les crustacés (Crustacea) du Luxembourg : aperçu historique. Bull. Soc. Nat. luxemb. 116: 381-390.
  • MNHNL, iNaturalist & GBIF, 2020. Pacifastacus leniusculus in MNHNL-mdata, online portal combining species observation from Recorder-Lux, iNaturalist and GBIF. National Museum of Natural History, Luxembourg. URL: [accessed 2020-03-13]
  • Ries, C., A. Arendt, C. Braunert, S. Christian, A. Dohet, A. Frantz, G. Geimer, M. Hellers, J. A. Massard, X. Mestdagh, R. Proess, N. Schneider & M. Pfeiffenschneider, 2017. Environmental impact assessment and black, watch and alert list classification after the ISEIA Protocol of invertebrates in Luxembourg. Bull. Soc. Nat. luxemb. 119: 63-70. [PDF 360 KB]
  • Wikipedia contributors, 2020. ‘Signal crayfish’, Wikipedia, The Free Encyclopedia, 31 January 2020, 01:54 UTC, <> [accessed 2020-03-13]

 Page content last updated on 2021-06-15. Last proofread by Caroline Grounds on 2019-12-11.