STUDYING INVERTEBRATES
Rivers support an array of both insect and non-insect invertebrates which can frequently be confusing. One way of understanding this variety is to think of the species in terms of 'functional feeding groups' in order to understand the function of the species in the habitat.

Algae cover the surfaces not only of stones and gravel but also the leaves and stems of higher plants. They support the 'grazer-scrapers'; snails (Gastropoda) and caddis larvae (Trichoptera) preferring to crop the hard surface of stones while some mayfly nyphs (Ephemeroptera) and midge larvae (Chironomidae) prefer to graze the softer plants.

The freshwater shrimp occurs in high densities in chalk streams and rivers. It can be thought of as a 'shredder' which breaks up and consumes plant material in the autumn such as leaves. By consuming the coarser material it itself provides a source of food for fish such as brown trout and bulheads while releasing a stream of finer plant material which is consumed by other invertebrates.