Water Beetle

Air supply

The great diving beetle breathes air, not water. It carries an air bubble trapped beneath its wing cases (elytra), pressed against spiracles (breathing holes) on the abdomen. This air supply allows it to stay submerged for several minutes before returning to the surface to replenish. The beetle rises tail-first to the surface film and opens its elytra slightly, exchanging the depleted bubble for fresh air. This system also acts as a physical gill — oxygen from the surrounding water diffuses into the bubble as it is used.

Formidable predator

The great diving beetle is a top predator in its aquatic habitat. Adults can overpower prey larger than themselves: they have been documented attacking and killing fish, newts, frogs, and tadpoles. Larvae are even more aggressive — they have hollow, grooved mandibles through which digestive enzymes are injected into prey, liquefying the internal tissues which are then sucked out. Larvae have been called “water tigers.”

Night flier

Despite being fully aquatic, great diving beetles retain fully functional flight wings. They disperse between water bodies by flying at night, attracted to light. This flight capability means new ponds are rapidly colonised — a well-constructed garden pond with no fish can have water beetles within weeks. Adult beetles are also attracted to the glint of car bonnets and tarmac at night, occasionally landing on roads in the mistaken belief they are water.

Sexual dimorphism

Male great diving beetles have smooth, shiny elytra; females have deeply grooved elytra. This is thought to help males grip females during mating in the underwater environment.