Diving beetle

If I was a small pond creature I would be very alarmed to see this swimming towards me. It's one of the great diving beetles Dytiscus dimidiatus, and is a mean predator, particularly the larvae which are not averse to snacking on tadpoles, newtpoles and small fish. In fact this is the largest of the six British species of great diving beetle, reaching 40mm in size, and is a rare insect being largely restricted to ancient fenland. The cream band around the margin and the pale brown underside are key identifying features. This one is a male, determined by the tarsi of its front legs which are modified into suckers for gripping the female during mating and the smooth elytra.