Our canals are a haven for wildlife. From the tiny larvae beneath the water to the invertebrates that fly above, there are plenty of species to find.
Common pond skater
Aquatic insects
Delve beneath the surface, and you’ll find a range of biodiversity. Here are a few of the aquatic insects that live in our canals.
Whirligig beetle
Scientific name: Gyrinus substriatus
Size: 5-7mm
Where to spot: Surface of ponds and slow-moving waters
These shiny black beetles look like dots on the water’s surface. With short and flat paddle-like back legs, whirligig beetles can shoot across the water in search of food. They are most easily identified by their orange legs, oval shape and distinctive whirling movements that give them their name.
Whirligig beetles have two sets of eyes – one to look forwards and one to look up.
Great diving beetle
Scientific name: Dytiscus marginalis
Size: 3cm
Where to spot: Well-vegetated still and slow-moving waters
Very large and a fearsome predator, the great diving beetle hunts tadpoles, invertebrates and even small fish. You can identify a great diving beetle by its size. They’re green-black in colour with yellow markings on the thorax and wings. Females have fine grooves on the wing cases; males have suction pads on their legs to grip females when mating. They are equally sizable and voracious as larvae, with strong jaws to catch their prey.
Lesser water boatman
Scientific name: Corixa punctata
Size: 1.5cm
Where to spot: Surface of ponds and slow-moving waters
The lesser water boatman has long green legs covered in tiny hairs. Resembling oars, these legs enable the water boatman to swim on the water’s surface. Adults are dark brown with yellow stripes and boat-like bodies.
Male lesser water boatmen ‘sing’ like grasshoppers to attract mates.
Common backswimmer
Scientific name: Notonecta glauca
Size: 1.4cm
Where to spot: Near the surface of ponds, ditches and canals
Swimming upside down, the common backswimmer traps air bubbles beneath the surface to breathe. They hunt by sensing the vibrations of prey, like smaller invertebrates and tadpoles. Charging at speed, the backswimmer stabs its victim with its beak and injects toxic saliva. Backswimmers are light brown with red eyes and oar-like legs.
Backswimmers are sometimes known as greater water boatmen.
Common mayfly
Scientific name: Ephemera danica
Size: 1.5-3cm
Where to spot: Still waters and fast-flowing rivers
Also known as the ‘green drake’, the common mayfly is one of 51 species in the UK. They spend their lives underwater as larvae, surfacing as adults to mate and reproduce. Adults have broad wings, short antennae and long tails.
Mayflies only live as adults for a very short time, some as little as a couple of hours.
Caddisfly
Scientific name: Trichoptera
Size: 2-28mm
Where to spot: Slow-flowing waters
Living underwater as larvae, caddisflies build casings out of the habitats they live in, like stone, sand, leaves or twigs, and spun together with their own silk. As adults, they look like moths, typically living on land near water.
There are about 200 species of Trichoptera.
Pond skater
Scientific name: Gerris lacustris
Size: 1.5cm
Where to spot: Surface of ponds and slow-moving waters
Skating across the water’s surface, pond skaters are predatory insects that gather in large groups. They’re identified by their long legs which have water-repellent hairs to help them walk on top of the water. Pond skaters can be confused with the water-measurer (smaller and more fragile-looking) or water crickets (shorter and sturdier bugs).
There are nine pond skater species in the UK.
Water scorpion
Scientific name: Nepa cinerea
Size: 3.5cm
Where to spot: Shallow and still waters
The water scorpion may have pincer-like legs and a long tail, but it’s not actually a scorpion. This creature hides among dead leaves, waiting to ambush small tadpoles or fish. While they live underwater, water scorpions are poor swimmers and prefer to walk. They use their long tails to siphon air from the surface.
Water stick insect
Scientific name: Ranatra linearis
Size: 5cm
Where to spot: Well-vegetated still and slow-moving waters
This relative of the water scorpion looks a lot like a mantis. Like scorpions, they have a snorkel-like tail to collect air from the surface of the water. The water stick insect hides amid reeds in its mantis-like pose under the water to ambush unsuspecting prey.
Water spider
Scientific name: Argyroneta aquatica
Size: 1.5cm
Where to spot: Well-vegetated still and slow-moving waters
Spending its life underwater, the water spider is unusual for its kind. They build bell-shaped webs amid aquatic plant stems and fill them with air collected from the surface using the hairs on their bodies. Water spiders spend their days in these air-filled webs and hunt at night.
Dragonfly and damselfly nymphs
Scientific name: Anisoptera and Zygoptera
Size: 2-4cm
Where to spot: Well-vegetated waters
Like their adult counterparts, dragonfly nymphs are voracious predators that hunt tadpoles and small fish. The smaller damselfly nymphs feed on invertebrates. Dragonfly nymphs have stocky bodies and can reach 4cm; damselfly nymphs are slenderer, reaching 2cm, and have three long, flat tails.
There is lots of life beneath the water – and you might find young amphibians as well as invertebrates.
Tadpoles
Tadpoles are the aquatic larval stage of amphibians, like frogs, toads and newts. Hatching from eggs (like frogspawn) in the water, tadpoles survive on algae and plant matter using gills to get oxygen. As they mature, tadpoles lose their gills, develop legs and start to eat insects and invertebrates.
Frog tadpoles are black, swarming in shallow water. They turn green-brown as they grow.
Toad tadpoles are also black, and similarly swim in groups, but are chunkier than frog tadpoles.
Newt tadpoles have feathery gills; great crested newt tadpoles are slightly larger than smooth or palmate larvae.
You might also find some small fish in our canals.
Stickleback
Scientific name: Gasterosteus aculaeatus
Size: 4-7cm
They may be small, but sticklebacks aggressively hunt tadpoles and other small fish. They’re also fiercely protective of their eggs. Sticklebacks have a brown back with silvery sides and three sharp spines on its back. Males develop bright red throats and undersides in the breeding season.
Sticklebacks are one of the most common freshwater fish in UK canals and rivers.
Minnow
Scientific name: Phoxinus phoxinus
Size: 4cm
Minnows are small fish, dark green in colour with striped bands along their sides. Females have a shiny white belly, while males have red undersides and pelvic fins. Minnows are found in most freshwaters across the UK.
These tiny fish form large shoals to spawn in shallow waters.
When exploring the wildlife along our canals and rivers, remember not to disturb protected species, like the great crested newt. Always take care near the water and keep back from the edge.
