One of the commonest waterside beetles, this terrestrial insect is found in lowland and upland areas wherever there is rough grassland. Look out for Soldier Beetles wherever you see lots of thistles of various kinds as well as members of the family Apiaceae (formerly referred to as the umbellifers) such as Wild Carrot, Hemlock Water-dropwort and Hogweed.
On breezy summer and autumn days, quite a few soldier beetles get blown onto the surface of streams and lakes, and they are an important food source for trout at such times, when aquatic insects are scarce. (The majority of aquatic insects are on the wing in spring and early summer.)
For more information about the Soldier Beetle, and tying details of suitable artificial flies (including a superb pattern devised by Taff Price) to imitate this important insect of upland streams and lakes, see Pat O'Reilly's guide to Matching the Hatch.
O'Reilly, Pat. (1997; 8th reprint 2010) Matching the Hatch. Shrewsbury: Quiller Publishing.
Foster G. N. & Friday L. E. (1988) Key to adults of the water beetles of Britain and Ireland (Part 1). Taunton: Field Studies Council.
Harde K.W. & Severa F. (1984) Field Guide in Colour to Beetles. Littlehampton Book Services.