How to catch trout during a mayfly hatch

Mayfly season might be known as duffer's fortnight, there's still skill involved to successfully catching trout during a Mayfly hatch.

Picture copyright © Jonathan Barnes
Fly fishing tips Estimated reading time 7 - 12 minutes

What are mayflies?

Mayflies are the largest up-winged fly species found in the UK. There are actually several different species of mayfly found in the UK and, depending on the weather conditions, most hatch between April and June, so they're not solely restricted to the month of May.

They tend to occur much later in the year the further north you go, and in the Yorkshire Dales they're most common in June, especially when the weather has been grim.

How long does the mayfly season last?

The duration of the mayfly season varies from place to place and year to year, but a couple of weeks is common. Fly fishers refer to the period as duffer's fortnight because if you're in the right place at the right time and are using the right fly, you stand a pretty solid chance of catching.

Since mayflies are so abundant during hatches, and because they're so big and meaty, trout get locked onto them and they'll take them - and any fly that resembles one - very confidently. In some places, including Ireland and the US, the mayfly hatches are so big that the adult insects can cover roads causing cars to skid and crash!

How long do mayflies live?

Mayflies are known as Ephemeroptera because they're ephemeral, or short-lived, and most live for anything from 30 minutes to a day at most in their flying form. During their very short life as a flying insect, they really have only one thing on their minds - reproduction.

Although the flying adults live for less than a day, the mayfly nymphs live for 1-3 years, and these too form the diet of trout when they're out in the open. 

Where are mayflies found?

Mayflies are most commonly associated with rivers and streams, however, you do also get them in UK stillwaters and some of the Irish loughs have huge mayfly hatches which draw in fly fishers from across the world.

Which mayfly species are most common in the UK?

Three ephemerid species are commonly found in the UK: Ephemera danica (the largest one), Ephemera vulgata and the more rarely seen Ephemera lineata. However, there are over 50 species of these little up-winged ephemeropteran flies known from the British Isles.

Other ephemeropterans include the olives of the Baetis genus and the tiny Caenis flies, known more commonly as the angler's curse, because it's so tricky to catch trout when they're locked onto feeding upon them.

How do you know when there will be a mayfly hatch?

Mayfly hatches are weather dependent but usually occur between late April and late June, depending on the conditions, so you need to be in the right place at the right time.

Mayflies typically start hatching in the late morning around 10 or 11am, but don't usually get going until the mid-afternoon.

Slightly damper days tend to be best. During hot weather, they'll hatch earlier in the day or later in the evening to avoid the heat, so consider getting up early or staying on late if there's no sign during sunnier weather.

Generally speaking, mayfly hatches go on for several days or a couple of weeks (again depending on the weather) so if you got lucky one night, you might be able to get a repeat performance the night after.

In what areas do mayfly hatch?

Mayflies are most associated with fertile chalkstreams, such as those of the south of England. However, you also find these flies in other less fertile waters, including streams and stillwaters across the rest of the UK.

They do seem to be most prolific in areas where the water is hard and alkaline, so chalkstreams and limestone rivers are the perfect place to seek them out. The hatches are most common in the siltier parts of the river, as this terrain forms the ideal home for the young nymphs.

How do you fish a mayfly hatch?

When a hatch starts it can take the trout a little while to "switch on" to feeding upon them - sometimes up to a couple of days. However, once they do, they'll pretty much take anything mayfly shaped that you care to chuck at them.

They can often lie in places where it's hard to reach them, like under trees and bushes, and they can still be spooked by a poorly presented fly or a line going over them, so you still need some skill and stealth.

What gear should I use?

While a standard four weight rod is ideal for fishing during a mayfly hatch, mayfly imitations are bigger and bulkier than most other dry flies you'll be fishing.

Their extra air resistance makes them tougher to cast and turn over neatly, so it's worth bumping up the size of your leader and tippet to aid turn over. You might also want to go up to a five or six weight rod if it's windy, as casting a big, bulky dry on a four weight in the wind isn't as easy as it is on a bigger or stiffer rod.

A heavier tippet and leader will help them turn over and improve presentation and also stops them twisting quite so much, which leads to less hassle in correcting twisty tippets. Anything from 6lb to 8lb tippet is probably about right for such big flies.

Thankfully, once the trout are really switched onto feeding on mayflies they're not really leader shy, so the thicker line than usual doesn't seem to have that much impact on bites. 

Where should I cast?

It's typically most productive to target a rising fish that's holding station in a river (or still water) and mopping up the mayflies landing on the surface or drifting past.

If you're in a river, try to land your fly upstream of the trout and let it drift through without dragging, otherwise the fish will realise it's unnatural and probably won't snaffle it.

Should I move my fly once it's landed?

Generally, you fish mayflies static in a dead drift so they float down the river at the same speed as the real mayflies that have landed upon the water surface.

However, at times - especially during a spinner fall - giving them a little twitch can make them resemble adults a little more and increase your chances of a take.

If there are loads of flies on the surface, it does seem logical that you want yours to stand out a little so the trout notice it and take your fly instead of the live but static ones.

How can I keep my mayfly pattern afloat?

It depends what it's made from. Personally, I favour a hydrophobic fumed silica desiccant like Frog's Fanny for my dries. This very light weight white powder comes in a little pot with a small brush attached to the lid. You carefully remove the brush and rub the powder into the fly every few casts and it will float like a cork.

Powdered floatants are great for most dry flies, especially CDC patterns, but other people favour a liquid floatant such as Gherke's Gink for keeping their mayflies afloat.

How quickly should I strike when a trout takes my dry fly?

Sometimes, I wish I knew the exact answer to this! The old theory is that you should say "God save the queen" as the fish takes your fly and then lift the rod.

If you strike too soon it's very common for the fish not to get hooked, and if you strike too slowly it can mouth and spit out the fly. However, striking more slowly does seem to work better, if you can stop your instinctive urge to raise the rod as soon as the fly is engulfed.

Which mayfly patterns should I take with me?

The Green drake mayfly pattern is designed to resemble Ephemera danica, so you'll definitely want plenty of these in your fly box during the early summer months. It's also worth having some emerger and nymph patterns on hand.

Spent gnat mayfly

Davie McPhail's Spent gnat mayfly pattern is made from 4mm white ethafoam and has a segmented body, so looks like the real thing and stays afloat all day. It's a little on the fiddly side to tie as it has a detached body, but it works brilliantly and looks spectacular.

Detached body mayfly emerger

Mak's Detached body mayfly emerger pattern is a more unusual pattern, but well worth trying when the flies are starting to hatch. It's also made from sheet foam, like Davie's version, and uses the same needle technique to form the body.

Mayfly nymph

When the mayfly aren't yet hatching, a mayfly nymph pattern can work wonders, as the nymphs are still present even if you can't see the adults. It's weighted with copper wire to help it get down to the bottom and it's a pattern that works just as well on stillwaters as it does on rivers.

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