Species description: A very striking blue crab with a wide carapace (twice as wide as it is long) that reaches sizes of up to 22 cm. Carapace colour can vary from grey-blue to blue-green on the upper surface, and is yellow-white on the underside. This species exhibits sexual dimorphism in mature individuals; in mature males parts of the pincer are bright blue and tips are red, and in mature females parts of the pincers are orange and tips are purple. Colouration can vary depending maturity and on moult cycle stage. There are 9 teeth on either side of the carapace with the 9th tooth being especially prominent, considerably longer and more pointed than the others. Pincers are long with several prominent spines on them. Fifth pair of legs end in flattened paddles. It is an active swimmer and can be aggressive.

Habitat: Found from lower shore to depths of up to 90 m, although more commonly 0-35 m. Burrows in muddy sand. Can tolerate a range salinity so is found in estuaries as well as deeper water. Egg laying and hatching occurs in estuaries, mature adults will migrate back to estuaries to breed. Juveniles have also been recorded in seagrasses in its native range or areas where this species has become established.

Distribution: The native range of this species is the western Atlantic, but it has been introduced in many areas outside of this. It is sold live in Britain and Ireland which is the potential source of any occurrences. Several sightings have been reported over the years throughout Britain and Ireland. In Ireland there have been recently reported sightings in Dublin Bay, and most recently in 2024 there were reports from Sussex, one live and one dead animal in Brighton; although it is still unclear if these are establishing (currently deemed unlikely) or were escapees or unintentional releases of live transported animals. Any sightings should be reported immediately.

Similar Species: Unlikely to be confused with any other species.

Key Identification Features:

• Large, striking blue crab.
• In mature males parts of the pincers are bright blue with red tips, in mature females they are orange with purple tips.
• Prominent spines on pincers.
• 9 teeth on either side of the carapace, 9th tooth considerably longer, more prominent and pointed than the others.

Distribution Map from NBN: Callinectes sapidus at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Callinectes sapidus at iNaturalist World Species Observations database.

WoRMS: Callinectes sapidus at World Register of Marine Species. Accepted name: Callinectes sapidus Rathbun, 1896. AphiaID: 107379.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Eucarida; Decapoda; Pleocyemata; Brachyura; Eubrachyura; Heterotremata; Portunoidea; Portunidae; Portuninae; Callinectes