Zebra Mussel - Dreissena polymorpha

Adults are up to 3 to 4 cm in length with a typical mussel shape. The shell is yellow with darker bands or zig-zags. It is highly variable, as suggested by its latin name, and some specimens lack the stripes and can be all white or all brown/black.

The most likely confusion is with the closely related Quagga Mussel Dreissena rostriformis bugensis which has now been found in our area. Though Quaggas grow to a larger size, young colonies generally comprise smaller mussels so this isn't a reliable guide. The easiest way to tell them apart is that the two shells of the Zebra Mussel join in a flat plane (ie. the shell is bilaterally symmetrical). A single shell should therefore lie flat on the ground. Quagga Mussels however are not symmetrical and the two shells fit together with a sinuous join and a single shell will wobble on a flat surface. The two also have a differently shaped outline. Zebra Mussels are roughly triangular with a prominent ridge whereas Quagga Mussels are more rounded, broadly 'D' shaped and lack the ridge. See Identification Aids for more details.

The False Dark Mussel Mytilopsis leucophaeta also has a similar shape to the Zebra Mussel but this is a brackish water species and has not been found in Leicestershire or Rutland.

• up to 4-5cm
• triangular shape
• pointed shell hinge end
• the two shells fit flatly together (bilaterally symmetrical)
• prominent ridge on the shell surface

Images should be submitted with your record showing the key ID features, otherwise include a comment explaining how you identified the species.

Lakes, canals. reservoirs and slow rivers. It attaches itself to solid surfaces such as walls, stones and other mussels. It can colonise soft sediments if dead mussel shells provide sufficient substrate for it to attach to. Larvae are sensitive to UV light so it is not normally found below 1m in depth where it can form huge colonies.

All year round

This is a non-native pest species that arrived in Britain in the 1820's. Since 1999 there has been a dramatic increase in its abundance and it can be a problem in water treatment or extraction facilities, such as at Rutland Water.

Widespread in England, but less common elsewhere in Britain.

Widespread but local in Leicestershire and Rutland.