Caddisflies

Trichoptera

- Caddis fly larva (Trichoptera)

Description/identification

Indeed, it is often not realised just how many different kinds there are – in Britain alone there are around 200 – and that they make up one of the most diverse groups of freshwater animals. Nearly half of UK caddisfly species have been found in ponds making caddis second only to beetles in their variety amongst the bigger pond animals.

Although, the underwater larvae are usually fairly easy to find, adult caddisflies can be quite hard to spot because many only fly at dusk or are nocturnal. Watch your garden pond as the sun is going down for small groups of fast darting flies with very long antennae flying low over the water – they will almost certainly be caddis flies.

Which caddisflies will you find in your pond?

Caddisflies are one of the groups of animals you would expect to see in practically all good quality ponds.

The commonest caddisflies, and most likely to be seen in garden ponds, are the group of around 30 species called Cinnamon Sedges, mostly in the genus Limnephilus. Also likely to turn up is a near relative of this group, the Mottled Sedge (Glyphotaelius pellucidus), and the dozen or so pond-dwelling members of the leptocerid family, including species known as Black Silverhorns. One of the pond leptocerids that you might see, Triaenodes bicolor, can be easily distinguished from the Cinnamon Sedge group because its larvae can swim through the water – they have long swimming legs. A good garden pond find would be the Two-spotted Great Reed Sedge (Phryganea bipunctata) – one of our biggest caddisflies – whose predatory larvae have a handsome and distinctive case.

Most caddis larvae have a case, but not all. Cases are made by gluing together with silk bits of plant or sand grains – sometimes even the shells of water snails – to camouflage and protect the soft-bodied larva from predators. The type of case materials used can give a clue to the identity of species, but are not usually the clinching identification feature; usually you need to look at very small body parts under the microscope. The Mottled Sedge is one exception with its distinctive case made of flat leaves.

Caddisflies live in both permanent and seasonal ponds and they can be especially abundant in shallow grassy ponds which dry out. Some are found in the tiniest of puddles: for example the endangered Window-winged Sedge (Hagenella clathrata) is only found in Britain in tiny pools at the base of clumps of rushes in bogs and heaths.

Caddisflies should have no difficulty reaching most garden ponds: flights of 5 km have been recorded and longer-distance movements seem quite possible.

Encouraging caddis flies to your pond

To attract caddisflies to your pond you will need the three key features of high quality garden ponds: clean water, shallow water and well-vegetated edges. For some of the Cinnamon Sedge group it’s also good to have overhanging vegetation around your pond as these caddises lay their eggs out of the water, including on trees and shrubs above the edge of the pond. If your pond has sand, dead leaves and live water plants there should be no shortage of suitable case-building materials.