European Stonefly

• Stoneflies are the aquatic insects most demanding of oxygen and the first to disappear at the slightest pollution, so their presence is the best sign of a river in excellent condition.
• The adults fly poorly and barely stray from the watercourse; many do not even feed.
• They communicate by drumming the abdomen against the substrate, with rhythmic patterns particular to each species that work as a recognition code.
• It is one of the best bioindicators of water quality in existence. Stoneflies are extraordinarily demanding about dissolved oxygen and vanish at the first sign of organic pollution, so their presence certifies a clean river.
• European biological water-quality indices, such as the IBMWP used in Spain, assign them the highest score for precisely that reason.
• The nymph is predatory and hunts the larvae of other insects beneath the stones of the riverbed; it takes two or three years to develop.
• The adult lives for a few weeks, flies poorly and hardly strays from the river; many species in the group do not even feed.
• They communicate by drumming: males and females tap their abdomens against the substrate, producing rhythmic sequences specific to each species, a vibratory language that takes the place of song.
• They are an ancient lineage, with fossils from the Permian, and they retain traits regarded as primitive among winged insects.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Fast, cold, highly oxygenated stretches of mountain streams and rivers

Sexual maturity

The male attracts the female by drumming his abdomen against the substrate and sending low-frequency vibrational signals; mating takes place on the ground or on vegetation

Gestation / incubation

The eggs are laid directly into the water and stick to stones and gravel; the nymph goes through 10-12 moults over one to three years before leaving the water for the final moult

Litter / clutch size

The female releases the eggs onto the water's surface or deposits them by dipping the tip of her abdomen; they sink to the bottom and stick to the substrate

Sources consulted: Wikipedia (es): Perla marginata · The Riverfly Partnership, ficha Plecoptera · First Nature · Fichas de identificacion de Perla marginata · Frutiger 1996, embriogenesis de Perla marginata a distintas temperaturas · Ortega & Tercedor 1991, ciclo biologico en Sierra Nevada (Granada) · The Riverfly Partnership

Best time: Adults in spring and early summer, perched on stones and bankside vegetation of cold, well-oxygenated rivers