Wildlife

A Dip in the Stour

An adult caddisfly does not live very long. The nymphs live underwater for up to two years, but the winged adults only live for a few weeks to months at the most. The adults don’t have developed mouth parts and are only able to sip liquids for their food, such as nectar. Their primary purpose is to reproduce.

As the evenings become longer and touched with golden light, and the air becomes warmer and dares us to leave our jackets at home, some of us migrate towards the riverside.

The irresistible draw of the tinkling flow over rocks or the reassuring glossy slide of deeper waters calms the mind and soul. Those who stop to peer beneath the water’s mirror sheen will be rewarded with a glimpse of a busy and bustling world, with inhabitants going about their multitudinous tasks, oblivious to the land of giants above.

One of these inhabitants, the caddisfly larvae, has a fascinating story.

My first introduction to caddisfly larvae was when my son showed me one in his hand.

“They’re everywhere”, he told me. “There’s a creature inside. I think the creature makes its own case to hide in.”

As usual, when it comes to matters of nature, he was right. The caddisfly, or sedge fly, is a large order of insects which can be found in all sorts of wetland. They are known for building cases around their bodies to shelter and then pupate inside. The caddisfly larvae gather sand, small stones and pieces of wood which they spin into a tube-like case with silk secreted from glands in their mouths. In this River Dipping in the Stour. Image: Sue Crookes way, the caddisfly larvae create The adult caddisfly will live for a portable shelter for themselves around a month, during which that perfectly matches the time the females lay eggs on riverbed. vegetation just by the water’s surface. On hatching, the larvae The larvae can emerge fall into the water and begin their head and legs immediately building a case to live in. When they are ready to from the case and pupate, the caddisfly larva will scuttle around, ready seal its case with a stone or to shrink back inside at piece of wood. It will then spin the first sign of danger, a cocoon of silk around its body as it undergoes metamorphosis looking exactly like a into its adult state, and the cycle piece of gravel. begins once again. Next time you’re picnicking, There are almost 200 species of paddling or messing about in caddisfly in the UK. The adults boats, take a moment to look are moth-like but with fine hairs at the riverbed. There might be on their wings instead of scales, more going on than you’d think. and wings that fold back along their bodies. Swarms of adult Find out what you can do to help caddisfly can be seen flying insects on the Dorset Wildlife above the surface of water in Trust website. late spring: a delectable buffet Melanie Fermor, for lurking fish. Dorset Wildlife Trust volunteer

The nymph underwater. The nymphs of larvae of caddisflies are what is so unique about these insects. They use silk from their body to build protective cases around their soft bodies to protect them. These cases are made of pebbles, sand and plant material.

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