There is an amazing diversity of wildlife living in water whether flowing water, still water or stagnant swamp and it all tends to be a battleground where species that feed on debris, algae or water plants are preyed upon by a great variety of predators. Some predators are stealthy, lurking amongst vegetation and grabbing unsuspecting prey with pincer like jaws (Dragonfly and Damselfly Nymphs) or grasping prey with their front legs (Water scorpions and Water Stick Insects). Aquatic insects have evolved from terrestrial insects so some have to leave water at some stages and also come to the surface of the water to obtain air, some only leave water to fly to find new ponds or streams.
In rivers Mayfly larvae mostly feed on debris though some may be predatory but when they leave water they may be preyed on by other insects such as this Damselfly or birds such as Martins Swallows and even Pied Wagtails. Mayflies that land on the surface of the water are grabbed from below by Trout. You can watch this happening along the Frome in early summer.
At the other extreme in stagnant water oxygen is in poor supply. Larvae of some midges known as Bloodworms have a type of Haemoglobin in their body fluid that holds oxygen as it does in our blood. Other insects such as the Rat-
Bloodworm, larva of a non-
It lives in more stagnant
Rat-
Drone Fly
Golden-
Above: Water Boatmen or Back swimmers.
Left: Lesser Water Boatman
A Dragonfly Nymph a voracious predator -
Right: a Water Scorpion has a short breathing tube and is also a predator.
Below:Water Stick Insect -
Both these species use stealth to catch prey
Above: A Diving Beetle, Streamlined shape, Holds a supply of air under its wing cases
Left: Larva of a Great Diving Beetle an extremely voracious predator.
Above: A Raft Spider one of Britain's largest spiders. Found on bog pools on the Bovington Ranges. It skates on the surface film and catches insects coming to the water surface for air.
Aquatic Invertebrates