Scottish stoneflies (Order: Plecoptera) are aquatic insects indicative of clean, fast-flowing water, with nymphs living under stones for 1–3 years before maturing. They are key bioindicators, with nymphs being carnivorous or herbivorous, and adults emerging in spring/summer to mate, acting as poor flyers near water.
Key Characteristics
Habitat: Primarily found in upland streams, rivers, and stony loch shores, requiring high-oxygenated, fast-flowing water.
Nymphs: Elongate bodies with two long cerci (tails) and, unlike mayflies, they lack gills on the abdomen, possessing them instead on the thorax.
Adults: Clumsy fliers often found near riverbanks, they have long antennae and wings that lie flat over their backs.
Diet: Nymphs are predators or shredders, while many adult species do not feed at all.
Life Cycle
The life cycle consists of three stages: egg, nymph, and adult.
Egg: Females deposit hundreds of eggs by dropping them into the water or tapping their abdomen on the surface. Eggs are coated in a sticky substance to adhere to the riverbed, often hatching in 2–3 weeks, though some species may exhibit egg dormancy.
Nymph: The nymphal stage lasts for 1 to 3 years, during which they undergo 12–36 moults.
Emergence & Adult: Nymphs crawl out of the water onto rocks or vegetation to undergo their final moult into winged adults. Adults live for a few weeks, with mating occurring on land.
Stonefly populations are sensitive to pollution, making their presence a sign of good water quality. They are crucial food sources for fish like trout and Atlantic salmon.