An imposing shadow rises from the depths of the pond, with a supple and quick swim. A surprisingly large, dark-shelled Carabean pierces the surface of the water for a moment, then disappears. The Dytic is back on the hunt.
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| picture credit: dytic.over-blog |
An aquatic beetle
Large family of beetles, the Dytiscidae have many genera in Europe, all well adapted to the aquatic environment. Eggs, larvae, adults, in their cycle everything happens under water. Only the nymphs make a brief excursion on the banks. Among more than a hundred species, the bordered dytic, Dytiscus marginalis, is one of the most common and most remarkable, by the size of the adult, 3 to 4 cm, its dark carapace, with elytra with metallic reflections, bordered of golden yellow. Its larva is no less astonishing, even larger than the adult, up to 6 cm, with a characteristic look, like an inverted question mark. Adults as well as larvae are merciless predators.
An aquatic life, an aerial breathing
If Dytics spend their life underwater, they have kept their aerial breathing, from the time of their distant terrestrial ancestors. Regularly, the adults go back to the surface, let emerge the end of their abdomen, capture air which they store between elytra and abdomen. Their reserve thus made, they spin in the vegetation. The larva has not adapted to aquatic breathing any more than the adult, no gills, no exchange membrane. It undulates towards the surface, head downwards, body arched, the end of its abdomen pierces the surface of the water, a drop of air is sucked in, feeding its network of tracheas.
The water tiger
The bordered Dytique has a reputation of voracious hunter. Deserved. Tadpoles, larvae, mud worms, fish, newts, no inhabitant of the pond is spared. And if the dytics regulate the inhabitants of the pond by cleaning up the populations, consuming the weakened and sick individuals, their pullulation can lead to the disappearance of all life in the pond. The adult, lying in wait in the vegetation, springs up with speed, following a lightning chase, the prey is captured, consumed with a crushing mouth apparatus.
Its larva is even more formidable. Thin, long, it carries a flattened head, provided with arched mandibles, spread out during the stalking. The prey passes, the mandibles close again. They have an action of claws, but also of syringes, instilling by two small channels of digestive juices which will liquefy the menu. Will not remain any more but to aspire it, by the mandibles also.
Just before becoming nymph, a larva can consume up to 30 preys per day.
Swimmer, diver, air sailor
The bordered dytic is a skilled swimmer, diver. Lively, fast, it has a body cut for swimming. Oval, flattened, carinated, bevelled, it splits the waters with ease. Its back legs equipped with natatory bristles row vigorously in a beautiful set. They handicap him however for the walk, of possible exits of water see him bumping painfully on the banks. On the other hand, if it walks badly, the Dytique can fly. The dark nights a light humming rises from the pond, the Dytics spread their elytra, spread their transparent wings, and fly away towards other spaces to live.
Males and females, aquatic meetings
The couples of Dytiques meet in spring, the males impregnate the females by maintaining themselves on their backs using the suction cups of their front legs. The eggs are aquatic, the larvae are born after 2 to 3 weeks, they will go through three stages before reaching the bank to become nymphs. Buried in the sand, in less than two weeks they will metamorphose into an adult still a little pale and soft, which will immediately return to the aquatic environment with its clumsy walk, where it can live for several years.
The bordered dytic is one of the most remarkable inhabitants of the pond, inviting itself according to its nocturnal flights, leaving without warning when the preys become scarce. A dense and varied vegetation, a diversified fauna, allow to perpetuate its presence, without excess however.
