The Riverfly 8 ….. key invertebrates which indicate the ecological health of the river

The RLA Riverfly team monitor 7 sites on the river every month to detect and count these species. Then that site gets a score which is then updated onto the national Riverfly Partnership Cartographer

Introducing #1 Cased Caddis!

Cased caddis larvae construct themselves a made to measure portable case to camouflage and protect their soft body from predators. These are made by sticking together small fragments of plants, twigs, grit …. in fact, any suitable material available using a silk like substance made in salivary glands close to their mouths. As the larva grows, more material is added at the front and the larva can turn around in the tube and trim the rear end so that it does not drag along the river bed!

Ingenious, practical and bespoke!

Sometimes they are difficult to spot until the head and front legs of the larvae come creeping out showing signs of life from a seemingly inert object. The cases are open at both ends and the larva draws oxygenated water through the back end, over the gills and pumps it out of the wider front end. It will move around more inside the tube to keep the oxygen level up.

When ready to hatch into their adult form, they glue their cases to rocks whilst they pupate from larvae to flying insects leaving these cases behind in the water. Depending on the species, this happens any time between February and November, the larva having been in this form for maybe one to two years!

So they undergo complete metamorphosis from egg to larva to pupa to adult. Eggs are laid by the flying adult which only lasts long enough to lay eggs and be eaten. Like many insects, the cased caddisflies are a very important part of the food web, providing a food source for fish and dippers.