The great diving beetle (Dytiscus marginalis) 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).
Both adults and larvae of this beetle are voracious predators, taking a wide range of prey including fish. They actively search for prey, and periodically swim to the surface in order to take in air (3). Adults often fly at night, and may land on glass surfaces or roads, mistaking them for water (2). When threatened, they exude a foul-smelling fluid from the anus that deters potential predators from eating them (5).
Females lay their eggs in cavities, which they cut in the stems of water plants that protrude from the water. The eggs hatch after a number of weeks (5).
This water beetle is common in most aquatic habitats, in both still and running water (3), and frequently occurs in garden ponds. The great diving beetle is scarcer in chalk and limestone areas (1), and seems to prefer ponds with plenty of weeds (4).
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