The Great Diving Beetle (Dytiscus marginalis) is a large aquatic insect found in Europe and northern Asia, common in Wales, much of England, and southern Scotland. Adults measure 27–35 millimeters, and larvae can reach up to 60 millimeters.
These beetles inhabit still or slow-running freshwater with vegetation and are dark on top and yellow underneath. Males have shiny wing cases with suction cups on their front legs for holding onto mates and prey. They are strong fliers, often using moonlight to find new water sources, and may mistakenly land on wet roads.
Before diving, they trap air bubbles in their wing cases. They reproduce by laying eggs underwater in aquatic plants, with an incubation period of 17 to 19 days.
