There are many stillwater flies imitating beetles. With over 4,000 aquatic and terrestrial beetles in the UK these are taken opportunistically by trout. Chafers particularly are found in the upland areas. Chafers or coch-y-bonddu is the welsh chafer. Chafers are about 1cm long and are brown with shell like wings. These are blown from deciduous trees and bushes on windy days in considerable numbers where they get gorged upon by trout.
Some trout develop a taste for aquatic beetles often small only 5mm long, these can often be seen swarming like buttons on the surface of still and slow moving waters.