Order Trichoptera - Caddis Flies

• Limnephilid Caddis Fly

Moth-like insects, with two pairs of membranous wings densely covered with tiny hairs and held roof-wise over the body at rest. All are fairly weak flyers and the females of a few species are wingless. Most are dull brownish or greyish insects, flying at dusk. Antennae very long and thread-like. Simple biting mouthparts, but these are poorly developed and often vestigial. The adults of some species feed on nectar, but most probably do not feed. Normally found near water. There is a complex metamorphosis, usually with five larval stages and a pupal stage. The young stages are nearly always aquatic, living in freshwater ponds, lakes, streams and rivers.

Most caddis larvae surround themselves with a protective case, made from various materials from their surroundings fastened together with a sticky silk-like secretion produced from a gland near the mouth. Each species uses its own particular materials - grains of sand, plant fragments and even empty snail shells - and builds its case to a specific design. It is often possible to identify a species simply from its case. The sand grains or other materials are frequently cemented together very neatly to form a mosaic. As the larva grows, it adds material to the front of the case. Case-bearing larvae have two strong hooks at the tip of the abdomen, which grip the silken lining of the case and ensure that the caddis and its home do not part company. Not all caddis larvae make cases - several species live in fixed silken nets which they spin among aquatic vegetation, and a few are free-living with neither cases nor nets. Larvae have strong biting mouthparts. Most of the case-bearing and net-living forms are omnivorous, feeding on any scraps of plant or animal matter they can find, but the free-living species are largely predatory.

Caddis Flies are closely related to the Lepidoptera (Butterflies and Moths) and structurally very similar to certain moths. Smaller members of the two groups are easily confused, but the hairy (not scaled) wings and the lack of a coiled proboscis will distinguish the Caddis Flies. The Order contains nearly 6,000 species, of which about 190 are represented in the British Isles.

Members of this family include some of the commonest caddis flies. They live mainly in and around slow-moving water of streams and rivers. Their larval cases are made from various materials and often quite large.

Adult of Caloptaulus sp. Typical caddis adult, with brownish coloured wings and body. Most species 15-20 mm long.

Photo: E.S. Ross ©

Adult (Caloptaulus sp.)

Larva of Limnephilus sp. Typical case-bearing caddis larva, with the head and legs protruding from the case, enabling the larva to move about in search of food. The case of this species is made largely from small, empty snail shells. Most species up to 25 mm long.

Photo: V.J. Stanek ©

Larva (Limnephilus sp.)