Scottish caddisflies (Trichoptera) are aquatic insects with a four-stage life cycle—egg, larva, pupa, adult—undergoing complete metamorphosis. Larvae are crucial, often building protective, portable cases from sand or plant debris (cased) or spinning nets to catch food (caseless). Adults are moth-like, short-lived, and usually non-feeding, appearing in mass "hatches".
Key Characteristics
Larval Cases/Habits: Divided into cased (using silk/debris) and caseless (free-living or net-spinners).
Adult Appearance: Moth-like with long antennae, usually drably colored (brown, tan, grey, or olive).
Habitat: Abundant in Scottish rivers, streams, and stillwaters.
Special Case: The Land caddis (Enoicyla pusilla) exists, which lives in woodland leaf litter rather than water, though it is not the main focus of Scottish aquatic ecology.
Life Cycle Stages
Eggs: Laid by females in jelly-like masses, often placed on or near the water surface.
Larvae: Spend most of their life underwater, feeding and growing through four moults. They are critical to the aquatic food chain and crucial prey for trout.
Pupae: Larvae seal themselves inside their cases (or a special cocoon for caseless types) to pupate.
Adults: The pupa swims to the surface to emerge. Most adults live only 1–2 weeks, focusing solely on mating.
Most Scottish caddisflies are univoltine, completing their life cycle in a single year, with larvae feeding actively even in cold water.