The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
Range & Status
The distribution of this species in the National Atlas (Kerney, 1999) would imply this is a nationally scarce species in Britain. However, subsequent surveys, especially in Dorset rivers, have resulted in many new records so the species would no longer warrant this status. In Cornwall the only records are from the Bude Canal (SS20C) and from the Tamar Lake Reservoir (SS21V). Both records date from 1973 and the species has not been refound, so its current status in Cornwall is unclear.
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.