The pond at the foot of my garden appears devoid of life, its unbroken surface reflecting the dull sky above. Weed hangs motionless and nothing stirs the thin sediment coating sunken leaves in the shallows. Every flooded ditch and waterlogged hollow in my area of west Dartmoor is brimming with gelatinous mounds of frogspawn, eyeballing me from the margins as if it has rained full stops. But my pool, dug with nature in mind, has none.
I know that creatures dwell in its muddy depths. A pond is a petri dish of potential, an experiment that generates life with the simple addition of water. Yet today, mine is reluctant to give up its secrets. I put it down to the cold.
Eventually I spot something darting up from the darkness. It pierces the flat surface membrane in the blink of an eye, a tiny ripple, and is gone. Another follows, quickly taking on air at the tip of its abdomen before battling buoyancy and furiously paddling down out of sight. Shaped like a seed pod, blackish-brown with gold edging and roughly 35mm long, this is one of our most striking water insects: the great diving beetle (Dytiscus marginalis).
A fast and formidable predator, this large beetle hunts any pond dwellers it can grab, whether invertebrates, tadpoles or even small fish. Its carnivorous larvae, armed with sickle-shaped jaws that inject deadly enzymes into prey, are just as fearsome.
I manage to scoop out one of the adults with an old rockpooling net for a closer look before returning it unharmed. Well adapted for an aquatic life, they carry oxygen supplies like a scuba diver and swim with feathery rear feet. They are also surprisingly strong fliers, enabling them to colonise new stretches of water, and are widespread in Britain. However, they are not always easy to see, only fleetingly surfacing for air, which they store beneath the rear of their wing cases.
At night they are bolder. When I revisit the pond after dark it is transformed. My torch picks out dragonfly larvae, water boatmen, grazing snails, palmate newts and, rowing frantically left and right like wind-up bath toys, three great diving beetles searching for their next meal.
