Order Plectoptera, Family Pteronarcys, Species californica

The name Plecoptera, comes from the Greek words "pleco" meaning folded and "ptera" meaning wing. The name comes from the insect’s pleated hind wings that fold under the front wings when it is resting.

What do stoneflies look like?

The nymph of the stone fly has long antennae with a flat body and widely separated legs. Each segment of its body is covered by a large “bony” plate. It has two antennae-like tails called cerci. These multi-part tail pieces actually work a lot like antennae – they help the insect sense what is around it.

The adult stonefly has long antennae and long veined front wings, often dark grey in colour. They can grow up to 4 cm in length. The back wings are shorter than the front wings and fold under the front wings so that you cannot see them when the stonefly is resting. The stonefly nymph does not lose its long tail parts when it becomes an adult. You can see them peeking out from under its wings.

Where do stoneflies live?

Stonefly nymphs usually live beneath stones in fast-moving, clean water.

Adult stoneflies are found near the streams and rivers from which they have emerged. They are not active fliers and usually remain near the ground where they feed on algae or lichens. Many adult stoneflies do not have mouth parts that work, so they cannot eat and they live only a short time.

Stoneflies are most common in cool, temperate climates. Different stonefly species are found all over the world – more than two thousand species!

Food for thought . . . stoneflies need clean, unpolluted water to live in. If there are no stoneflies near a river, does that tell you that the river is polluted?

What is the life cycle of the stonefly?

Eggs are laid in the water or are placed in cracks near the waters edge. They eggs sink and disperse. Some eggs are coated with a sticky slime that adheres to rocks and keeps the eggs from washing away in fast moving water.

Click here to see the life cycle of a stonefly

The larvae hatch in early spring. After the eggs hatch, the tiny nymphs feed on algae and rotting vegetation. As they grow the nymphs moult (shed their outer skeleton so that they can grow) often more than a dozen times before they become adults. Some nymphs take a year to become adults, some take two years.

Adults emerge near the edge of the stream, sometimes when the ice has just melted. Most appear to emerge at night. After emerging the adults fly.

In some species the adults feed and in others they don't. The non-feeding species emerge with fully formed eggs, mate quickly, lay their eggs and die in a few days. Some females of the feeding species live for 4 to 5 weeks.

To attract mates, male stoneflies drum (beat their abdomen on what ever they are standing on) to attract females, and females drum in reply. Females only mate once, lay their eggs and die shortly afterwards.

Food for thought . . . stone flies are very similar to their ancestors that lived up to 300 million years ago. In fact, fossils of the stonefly are almost the same as the ones you can see by the river side today.