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You have the names inverted and it would be safer going with just an ID of Dytiscus as there are 4 species which you could not separate from this image.
Chris Brooks - www.dragonfly-images.co.uk
My Flickr site - www.flickr.com/photos/ceb1298
Lat/Lng: 52.6051, 1.4543
OS grid ref: TG339064