Phylum: Arthropoda - Class: Insecta - Order: Coleoptera - Family: Cantharidae
One of the commonest waterside beetles, this terrestrial insect is found in lowland and upland areas wherever there is rough grassland. Look out for this particular Soldier Beetles wherever you see lots of thistles of various kinds. Like several other similar 'soldier beetles', they are also attracted to various members of the family Apiaceae (formerly referred to as the umbellifers) such as Wild Carrot, Hemlock Water-dropwort and Hogweed.
The head, thorax and abdomen are orange-brown, but the wing cases are very variable and can be orange, brown or almost black depending on the subspecies. Males have much larger eyes than females. At 10 to 15mm long, this species is rather larger than the Common Soldier Beetle Rhagonycha fulva, which is also seen most often on 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 the superb pattern pictured below, which was 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. (1st Edition 1997; 8th reprint 2010; fully revised 2nd Edition 2017) 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.