Skaters and Swimmers

In the calm water of ponds, deadly predators are on the move. Diving beetles scud through the shallows, grabbing small fish and insects with their sharp claws. Water boatmen hang just beneath the surface, waiting to stab flying insects that crash-land. On the surface itself, pondskaters wait for their victims, feeling for tiny ripples that pinpoint struggling prey. About one in 20 insect species live in watery surroundings such as ponds, lakes, rivers, and streams. Some spend their whole lives in freshwater, while others grow up in it and then fly away.

SURFACE TENSION
Instead of floating, pondskaters use surface tension to walk on water. Surface tension is a force that pulls water molecules together. When the water is calm, it makes the surface behave like a thin sheet. Pondskaters have light bodies and waterrepellent feet, so they can stand on the surface without sinking through it. This photograph, taken under a special light, shows how the water makes dimples around a pondskater’s feet.

WATER SCORPION
Although they live in water, most freshwater insects breathe air. The water scorpion gets its air supplies through a long snorkel, which it pushes up through the surface. The snorkel passes air to its tracheal system, which delivers oxygen throughout its body. Water scorpions are carnivorous bugs, and they stalk small fish and insects in muddy water. Their weapons are stealth, good camouflage, and two strong front legs that grip and spear their prey.

PONDSKATER
Seen from the side, this pondskater shows its piercing mouthparts and long slender legs. Pondskaters eat insects that have become stranded on the surface. They use their front legs to grip their food, their middle legs to swim, and their back legs to steer. Pondskaters are true bugs, and most of them have well-developed wings. They can fly, so it is easy for them to spread from pond to pond.

MAYFLY NYMPH
Mayfly nymphs that live in running water have flattened bodies and strong legs – features that prevent them from being washed away. Instead of breathing air from the surface, they collect oxygen through two rows of feathery gills. The nymphs spend up to three years underwater, preparing for an adult life that lasts less than a day.

GREAT DIVING BEETLE
With bodies up to 5 cm (2 in) long, diving beetles are powerful freshwater hunters. They swim with their back legs, speeding through the water. Before each dive, they store air under their wing cases, and they have to kick hard to stop themselves bobbing up to the surface. Diving beetle larvae are even more aggressive than their parents, with powerful jaws that can kill tadpoles and small fish.

SAUCER BUG
Like most freshwater bugs, saucer bugs are hunters, and they grip their victims with their front legs, which can snap shut like a pair of penknives. Saucer bugs lurk on the bottom of ponds, and their camouflage helps them to hunt. They surface to breathe, but afterwards they quickly dive back to the bottom, to hide among plants or in mud.

WHIRLIGIG BEETLES
Predatory insects often lie in wait, but whirligig beetles are always on the move. Like tiny black boats, they spin around on the surface, watching for small insects that have fallen in. A whirligig’s eyes are divided into two parts. One part looks above the surface, while the other part looks at the water underneath. This all-round view means that whirligigs can dive after food, and spot danger from above and below. Adult whirligigs spend the winter buried in mud at the bottom of ponds.

PHANTOM MIDGE LARVA
With its transparent body, the phantom midge larva is an almost invisible hunter. It hangs motionless in water, and snags small animals with its hook-shaped antennae. To change its depth, it adjusts two pairs of onboard buoyancy tanks, which make it rise and fall like a submarine. In summer, the adults often gather in dense swarms that look like clouds of smoke.

BACKSWIMMER
Hanging beneath the water’s surface, the backswimmer spends its entire life upside down. Like pondskaters, it eats insects that have crashlanded, but it attacks them from below. Its extra-long hindlegs work like a pair of oars, and it uses them to swim towards its prey. Backswimmers have big eyes, and they always keep their fronts towards the light. If they are put in a tank that is lit from the bottom, they swim the right way up.

DRAGONFLY NYMPH
Young dragonflies – known as nymphs – rely on stealth to hunt. They crawl along the bottom of ponds and lakes and up water plants, watching for prey. If a tadpole or small fish wanders near, they spear it with their telescopic jaws. The nymphs breathe by sucking water in and out of their abdomens. If danger threatens, they squeeze water out of their abdomens like jet engines – the perfect high-speed getaway.