The underwater insect calendar: UK river flies through the year
Course pack: Insect sampling sheet and 12-month river calendar. Coach Willy, our virtual AI coach, can explain each step, set you a practice task and check your understanding.
Who it's for
You're confident on the bank and want the finer details. Aimed at trout, grayling.
Where and when
Done on the bank. Best in: all.
What you'll work through
- 1Mayflies, caddis, stoneflies and midges: the right life stages
- 2Habitat and water quality
- 3A month-by-month UK guide (not fixed dates)
- 4How trout and grayling feed selectively
- 5Recording your river and Riverfly schemes
Step 1: Mayflies, caddis, stoneflies and midges: the right life stages
Alright mate, let's get stuck into the underwater insect calendar: UK river flies through the year. I'll walk you through what to look for, what to try and how to tell whether it helped. We'll start with mayflies, caddis, stoneflies and midges: the right life stages, then work through a proper practice job at each step. Take it at your own pace and keep a few notes so you've got a useful plan for next time.
By the end of this step
Have a go at: mayflies, caddis, stoneflies and midges: the right life stages.
Willy’s take
Let's get to know the main insects trout and grayling eat. In the UK, the big groups are mayflies (Ephemeroptera), caddisflies (Trichoptera), stoneflies (Plecoptera) and chironomids (non-biting midges).
Mayflies have an aquatic nymph stage, then hatch into a dun (sub-imago), then moult into a spinner (imago), which mates and dies, often falling spent on the water. Caddisflies have larvae (some in cases), then pupae, then adults that look like moths. Stoneflies have nymphs that crawl out to hatch on land.
Chironomids have larvae (bloodworms), pupae that rise to the surface and adults that hatch.
Each group has different stages, and trout might feed on any of them.
Kit I'd start with
- For this course, you'll need a small net or sieve for sampling insects, a white tray for sorting them and a magnifying glass. Polarised glasses help you see rises and insects. A notebook or log is essential. Carry a range of flies in different stages: nymphs, emergers, duns and spinners.
- Most importantly, return insects to the water after looking at them and avoid disturbing habitats.
- Return any insects you sample gently to where you found them, and keep dated notes, because hatches shift with weather, region and river type, and a few seasons of your own records will give you a far more accurate calendar than any fixed list of dates.
On the bank
Worked example
Imagine this: you see small moth-like insects fluttering over the river at dusk. Trout are rising, but ignore your mayfly dun.
Your turn: Mayflies, caddis, stoneflies and midges: the right life stages
- 1
Identify the insects you see: mayfly, caddis, stonefly or chironomid
- 2
Note the life stage: nymph, larva, pupa or adult
That's the free sample — this is where it stops
The full step keeps going with the rest of the practice job, common mistakes and fixes, a check-your-understanding quiz and your Insect sampling sheet and 12-month river calendar. Then 4 more steps, each with its own task, and Coach Willy on hand to talk it through.
You've read the free sample
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