Crayfish (Decapoda)
All images on this website have been taken in Leicestershire and Rutland by NatureSpot members. We welcome new contributions - just register and use the Submit Records form to post your photos. Click on any image below to visit the species page. The RED / AMBER / GREEN dots indicate how easy it is to identify the species - see our Identification Difficulty page for more information. A coloured rating followed by an exclamation mark denotes that different ID difficulties apply to either males and females or to the larvae - see the species page for more detail.
Crustacea - Woodlice, Crayfish etc.
Crustacea are a large group of Arthopod invertebrates. Many of them are aquatic, living in marine or freshwater environments, but the familiar terrestrial Woodlice are Crustacea in the Order Isopoda, along with freshwater Waterlice or hoglice, plus a few marine species. Crayfish are in the Order Decapoda - literally meaning 'ten footed' - which also include marine lobsters and crabs. Shrimps are now placed in the Order Amphipoda, which includes marine and freshwater species.
Crustacea include many thousands of tiny freshwater species that are planktonic (living in the water) or benthic (found in sediments). These include the Water-fleas (Diplostraca or Cladocera), Copepods (e.g. the Orders Cyclopoida, Harpacticoida and Calanoida) and Ostrocods. Their position at the lower levels of the aquatic food-chain means they are of great ecological importance.
The 'Practical Guide to Identifying Freshwater Crustacean Zooplankton' by L M Whitty (2004) has helpful guidance on how to identify these smaller species (despite being based on North American species). The Freshwater Biological Association has published keys for several groups of aquatic Crustacea.
Some Crustacea are parasitic, like the Fish lice in the family Argulidae.
Crayfish (Decapoda)
There is one native species, the White-clawed Crayfish, which is legally protected because of its serious decline in the UK. The other species found in the UK are all introduced or escaped non-native species.
The American Signal Crayfish is now common throughout the UK and has very rapidly spread through Leicestershire and Rutland, displacing the native crayfish from most of our watercourses. It is a much bigger species, which breeds faster and is capable of dispersing over land. It out-competes the native White-clawed for habitat and food and shelter, but it also carries a fungal pathogen ('crayfish plague') which our native species are very vulnerable to. This is thought to be the main cause of the decline in White-clawed Crayfish. To avoid spreading the disease, it is very important to disinfect or completely dry out all angling or water-sampling kit (waders, nets, rods, wetsuits, etc) before using again.
Native species are more likely to survive in isolated water-bodies where Signal Crayfish is less likely to colonise, such as Stoney Cove, where it is believed there is still a thriving population.
Further information on Crayfish is on Buglife's website - 'Crayfish Identification, Distribution and Legislation'
