Scottish mayflies (Order Ephemeroptera) are aquatic insects known for having a long, multi-year larval life as nymphs and a very short, non-feeding adult life focused on breeding. They are indicators of clean, well-oxygenated water. Adults are unique for having two winged stages (sub-imago and imago) and are vital food for trout and salmon.
Characteristics
Nymphs (Naiads): Aquatic, living under stones or in mud for 1–2 years, feeding on algae and vegetable matter.
Adults (Duns/Spinners): Have two or three long, thread-like tails, large front wings, and small hind wings. They do not eat, as their mouthparts are non-functional.
Appearance: Commonly feature a pale yellow-brown body.
Sensitivities: Highly sensitive to pollution, making them key indicators of, for example, high-quality, clean river water.
Life Cycle
Egg: Laid by females on the water surface, sinking to the riverbed.
Nymph: Hatches from the egg and spends months to up to 2 years developing in the water.
Sub-imago (Dun): The nymph swims to the surface, emerges, and flies to nearby vegetation to dry its wings. This is the first winged stage.
Imago (Spinner): The sub-imago moults again (the only insect to do so after having functional wings) into a sexually mature, often translucent-winged adult.
Mating & Death: Males form swarms over the water, where they mate with females. Females then lay eggs, and both die shortly after, often within a few hours to days.