Key for the identification of British Dytiscidae

The Dytiscidae are a group of water beetles with a good number of species in Britain.  They are characterised by long thread-like antennae and include quite a few large species.  The document below should enable you to identify your beetle to species.  Alternative keys and illustrations should be sought in Foster & Friday (2011) available here http://www.field-studies-council.org/publications/pubs/key-to-adults-of-the-water-beetles-of-britain-and-ireland-(part-1).aspx.