Identification | Mitten Crab Watch

Add a record

If you see a mitten crab, a sighting report requires:
- a clear photograph of the individual
- the number of crabs seen
- the exact location, time and date of the sighting

If you have the iNaturalist app (available on iOS and
Android), a useful tool to record any wildlife sightings both in the UK and overseas, you can submit the record directly on the app or via the iNaturalistUK website.

You can download a Mitten Crab ID guide from NNSS here.

You can also upload records to iRecord, which like iNaturalistUK, shares the data with the NBN Atlas, a national biodiversity database.

Alternatively, you can email the Marine Biological Association through dassh.enquiries@mba.ac.uk with your photograph, location, time and date of the sighting and they can record the sighting for you.

Identification

Mitten Crabs can be easily confused with other species. The following list of features will help you to identify them:

Grey-green to dark brown crab
Long walking legs
Squarish body up to 86 mm across
4+4+4 pattern of teeth around front of shell (Fig 1.)
Dense brown 'fur' on the white-tipped claws (Fig 2.)
Habitat: rivers, brackish water estuaries, rarely along the marine inshore coast
Juveniles may lack 'fur' on claws

You can download the GB non-native species secretariat (NNSS) Mitten Crab ID guide here.

Fig 1. 4+4+4 spine configuration.

Fig 2. Mitten Crab claw.

Similar Species

Broad clawed porcelain crab (Porcellana platycheles).

2 long antennae
Only 3 pairs of walking legs apparent
Found on the sea shore but never in freshwater rivers

Common shore crab (Carcinus maenas).

Lacks 'fur' on claws
Shell shape more triangular
Found on the sea shore and in estuaries but never in freshwater rivers