Stir Up Trout!

14 July 2022 | Sarah

There’s a small olive coloured upwing species that despite its tiny size, causes quite a stir with trout on warm summer evenings.

We’re talking about the Blue-winged olive (BWO). On rivers and streams across the UK this wee fly will have trout queuing up as the light fades.

To get the best of any hatch, it’s vital we understand the life cycle of this unassuming insect. After hatching from eggs, miniscule nymphs spend one year beneath the surface developing.

As they grow these nymphs actually moult several times, very much like a snake that sheds its skin.

In the life cycle Blue Winged Olives the sub imago is known as the “Dun” and the imago is known as the “Spinner”.

Come summer months, typically late June through to early September the now ripe nymphs swim to the surface to emerge into a dun (sub imago). You can visualize this as a butterfly emerging from its chrysalis. After their maiden flight, newly emerged duns take to the trees to undergo another transformation to the sexually mature adult, known in angling circles as “spinners”.

The spinner stage (imago) of BWOs is short lived, often 24-36 hrs. And mating within that short period, female spinners return to open water to deposit their precious cargo of eggs. Carried on the underside of their abdomen, these egg balls sink to the stream bed, or adhere to nearby vegetation, like submerged reed stems. Following a short incubation period the eggs hatch to complete the life cycle.

This information now allows us to make educated fly selection, which in turn will hopefully lead to success.

For the hatching duns, which takes place during the early evening, we should look to emerger style patterns that have the bulk of the body suspended subsurface.

When it comes to imitating newly emerged duns, which sit patiently at the surface waiting for their wings to harden, hackled dry flies work best.

In particular now the parachute style of dressing seems extremely popular.

Perhaps the main reason is that hackles arranged in the para-style are extremely buoyant.

As dusk approaches, female spinners return to lay their eggs under the cover of darkness.

Catch it right now and the activity is nothing short of spectacular as often thousands of spinners descend at one sitting, sending the trout into overdrive.

Making your fly stand out in the crowd can be problematic now though we suggest stepping up by one fly size to make your offering more obvious.

We haven’t really mentioned the nymphal form with good reason. It’s that with so much opportunity at the surface, why fish nymphs when you can be enjoying the more visual aspect of fly fishing, which I’m sure many would agree is the pinnacle of our sport!