The great diving beetle is, as the name suggests, a large aquatic beetle (4). It is has a beautifully streamlined body shape and is dark brown to blackish in colour with yellow legs and a yellow border around both the head and the thorax. The wing cases, or 'elytra', are ridged in females but smooth in males. Males can also be distinguished from females by the presence of suction pads on the front legs; two of which are very large. The brownish larvae have large heads, which bear impressive, large jaws (3).