Insects and their Allies  

Plecoptera: stoneflies

Stoneflies are soft-bodied insects that can grow up to 50 millimetres long with a wingspan of 100 millimetres. Adult stoneflies are always found near freshwater as they have aquatic larvae and as adults they are not powerful fliers. They therefore have poor dispersal capabilities are rarely move far from the place they were born. Stoneflies are recognisable by the following characteristics:

Trinotoperla species
Trinotoperla species

  • Elongated, flattened, soft body
  • 2 pairs of membranous wings that are held curved around the body at rest. Some species are wingless while others have reduced wings
  • Hind wings slightly wider than forewings
  • Long legs
  • 2 cerci at tip of abdomen

The larvae of stoneflies are aquatic and appear similar to the adults but lack wings. Larvae also possess external gills along the edge of their abdomens and at the tip.

Trinotoperla species larvae
Trinotoperla species larvae

Trinotoperla species belong to the GRIPOPTERYGIDAE family of stoneflies which consists of mostly dull-coloured insects ranging from very small to large in size. Trinotoperla species are commonly large, with a wing span of more than 30 millimetres. Most are uniformly dull-coloured with a slight darkening at the base of the wings. Adults are found throughout the summer months, although some of the smaller species of GRIPOPTERYGIDAE are more common during spring. The larvae of this family have an obvious tuft or rosette of filiform anal gills which can range from white through to pink or pale mauve in colour. The larvae can be found clinging to the underside of rocks and other debris in fast flowing water.

Life Cycle
Adult stoneflies live and mate near water, as their larvae are fully aquatic. Female stoneflies lay their eggs on the water as they fly slowly over it, or let them drop freely to the water while resting on overhanging rocks or logs. Approximately 100 to 1000 eggs may by laid and development of the larvae is slow, taking from 1-3 years. Depending on the species, stonefly larvae can moult up to 15 times before reaching maturity.

Adult stoneflies are herbivorous and usually feed on algae, lichens, rotting wood or other detritus. The larvae are mostly herbivorous also and feed on a wide variety of small plants, algae or dead plant matter, although some species are carnivorous.

Stoneflies prefer freshwater habitats and their surrounds, and adults can be found resting during the day on tree trunks alongside streams and lakes. The larvae are aquatic and can sometimes be found among the gravel on the bottom of fast flowing streams and well aerated lakes.