This larva is little more than two weeks old. The posture of the body is clearly an "S or question mark shape", typical of the Dytiscus larva. You can also see the swimming hairs on the legs, which are useful when the larva performs its slow paddling swimming and the hair fringes on the last segments of the body, which are used when the larva is fleeing from a possible threat and it makes a few powerful strokes with its tail. The tip of the tail is white because there's a small air bubble there that reflects the light. This is the spot where the air from above the water is let in during respiration, when the larva is floating with it's tail tip pressed against the water surface. It maintains a correct position by the support of the two thin appendages (cerci) on the tail tip.