Spiders that weave bubbles of air, larvae that catch their food in a net and floating bugs that use their legs as oars – who knew water beasties could be so fascinating? Words: Abigail Whyte
What species of wildlife springs to mind when you think of a river or a canal? The electric blue kingfisher? The lithe otter? The trout? We're focusing our magnifying glass on some unsung heroes – invertebrates.
Without these creatures the water’s ecosystems would collapse, depriving amphibians, fish, birds and aquatic mammals of the food they rely upon. They're also vital indicators of the state of a canal or a river: stonefly can only tolerate very clean water, while aquatic worms thrive in sluggish, silty conditions.
On top of all that, they're fascinating creatures that have adapted their own ingenious ways to surviving above or below the water surface. We've honed in on five species that spark our curiosity…
Caddisfly larvae, Trichoptera
What does it look like?Caterpillar-like, short, fat body with a dark head, enveloped in a protective casing of silk threads weaved with grains of sand, tiny leaf fragments and twigs. Adult caddisflies resemble moths.
Where can you find it?Glued to rocks and vegetation on the riverbed wrapped in its protective casing. You can also find the discarded casings (after the larvae has pupated) floating on the water's surface.
What does it eat?Fragments of plant material, living and dead organisms. Some species produce silk nets to capture food floating past.
What eats it?Trout, salmon and other fish.
Did you know…?The caddisfly takes its name from the caddisman (old word for pedlar) who wandered the countryside covered in samples of his wares, much like the larvae covered in bits of leaf, twig and sand.
What does it look like?Brightly-coloured creature with four large wings and enormous eyes that cover the top and sides of its head. When resting, their wings lie straight out beside their body, whereas damselflies, which they're commonly mistaken for, rest with their wings touching above their body.
Where can you find it?Hovering above the water's surface around rivers, streams, bogs, lakes and wetlands – although it’s their larvae you’re most likely to see in the water.
What does it eat?Other invertebrates, including mosquitos, spiders and even other dragonflies.
What eats it?Fish, birds and amphibians. The larvae are eaten by frogs, toads, newts, fish and kingfishers.
Did you know…?Dragonflies are among the fastest and oldest insects in the world achieving speeds of 35 to 60 miles an hour and some fossilised remains have been found to be over 300 million years old, with wingspans of up to one metre.
Lesser water boatman, Corixa punctata
What does it look like? Its tiny brown and yellow-striped body resembles a tiny boat – its hairy hind legs acting as oars. Unlike the backswimmer (which it often gets mistaken for) it doesn't swim upside down.
Where can you find it?Widespread in ponds, lakes and slow moving rivers. If you're lucky you'll see it paddling across the water's surface but it spends most of its time submerged, only resurfacing to come up for air.
What does it feed on?Algae and dead vegetation.
What eats it?Fish and the Diving Bell Spider.
Did you know…?When diving it carries a store of air in its coat of bristles so it can breathe underwater, which gives the bug a silvery appearance. In summer, it makes a soft chirping sound, like a cricket.
Diving Bell Spider, Argyroneta aquatica
What does it look like?Velvet grey in colour (although in water is has a silvery appearance) with short hairs covering its abdomen and legs. This is one of the few species of spider where males are larger than females.
Where can you find it?Ponds, slow moving streams and rivers.
What does it feed on?Water mites, water boatmen and other aquatic invertebrates.
Did you know…?They spin amazing sub-aquatic webs, which they fill with air so they can breathe underwater. The bubble acts like a gill, extracting oxygen from the water and dispersing carbon dioxide.
Great Pond Snail, Lymnaea stagnalis
What does it look like?As the name suggests, this is the largest pond snail in Britain (up to 8cm) with a grey body and a shiny yellowish brown cone-shaped shell.
Where can you find it?Common and widespread in England; less so in Scotland and Wales.
What does it feed on?Mainly algae and decaying organic matter. They can even occasionally be cannibalistic. It feeds with a tongue-like organ called a radula, which acts like a conveyor belt bringing bits of food to its mouth.
What eats it?Crayfish, fish and large insects.
Did you know…?To avoid being eaten, aquatic snails try to build the hardest shell possible, which requires high levels of calcium carbonate in the water.
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