Common medium stonefly

Common Medium Stonefly

Common Medium Stonefly ©

Common medium stonefly

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Scientific name: Diura bicaudata
As the name suggests, the Common medium stonefly is found in gravelly upland rivers and streams, often on bankside stones and plants. There are 34 species of Stonefly in the UK, which are hard to tell apart.

Top facts


Length: up to 3cm

Conservation status


When to see

January to December


The Common medium, or 'Predatory', stonefly is one of 34 species of stonefly in the UK, and is on the wing from April until June (nymphs are present all year-round). Stoneflies are common around fast-flowing, upland streams and rivers, but can be found in some still waters. The larvae spend their lives hiding among the gravels and feeding on algae, plants and invertebrates. The adults hatch out, usually in the summer, and do not travel very far from the stream; they are often found on riverside rocks and trees. Mating usually occurs on the ground, the female heading to the water to lay her eggs by dipping the tip of her abdomen in.

What to look for

Stoneflies are fairly robust invertebrates with narrow, dark wings, long antennae and two stout tail bristles. They fold their wings flat over their bodies when at rest. The Common medium stonefly is dark brown with orange patches at the back of its head and in front of its wings. Stonefly larvae also have two 'tails' and have a habit of clinging to the undersides of rocks in fast-flowing water.

Where to find

Widespread in upland areas in the west and north of the UK.

Did you know?

The Northern February Red (Brachyptera putata) stonefly is only found in the UK.