The Mayfly is a member of the Ephemera family, there are three mayflies commonly found in the British Isles, these are Ephemera danica, Ephemera vulgata & Ephemera lineata, for the purposes of this email we are treating them all as one (as the differences as negligible). Mayflies can be found in both still running water, but the majority are found on our rivers, it does not seem to matter the strength of the flow. Mayflies are found throughout the British Isles in all types of river and stream. They are easily identified in May and June as they will be the biggest up-winged fly on the water and white in colour. Mayflies can range quite considerably in size, from 15 to 25mm long (usually a size 14 to size 10 hook).

Where To Find Them

Mayflies are found in every part of the British Isles. They are especially prolific in any river which has a silty bottom (fnar fnar - one for the Viz readers!).
As with most of the up-winged family of flies, the Mayfly can be found in all running waters.

When To Find Them

The Mayfly hatch usually starts in the first two weeks of May and will continue until the end of June, depending on which part of the British Isles you are located.
Mayflies usually start to hatch in the south from the second week of May, lasting for around 4 weeks. The further north you go the later the hatches start, in Scotland the Mayfly hatch is normally around two weeks behind the south, starting at the end of May and continuing until the end of June. 

What To Look For

Mayflies are not renowned for their timing, but you can usually expect to see a hatch start (if it's a nice, warm day) sometime in the afternoon between 1pm and 2pm and it can continue until around 6pm. Initially, hatches will be quite sporadic, gradually increasing through to a crescendo later in the afternoon. It's like ringing the dinner bell for the trout!
Hatches of Mayfly can be very localised, one pool may be on fire - and the one just a few yards upstream completely devoid of life.
It is also worth noting that you may find very heavy hatches of Mayflies when it is very warm and sunny. you may also struggle to catch using a mayfly pattern and wonder why? This is usually because the trout take a few days to actually realise that the Mayfly are hatching, but once they do, they will rarely take anything else.


The lifecycle of the Mayfly is outlined below. The Mayfly is one of the up-winged flies where all of the stages can be imitated by the fly angler.

Mayfly nymphs are quite large and are found in the silt of a river/lake bed. The nymphal stage usually lasts either one or two years where they are buried in the silt. When the nymphs emerge the best imitation for these is a fat, long nymph (beaded when used in heavier flows). When imitating the Mayfly nymph, please take note of the body thickness, the body should be thick and long. Mayfly nymphs can be up to 25mm long and 5 to 7mm wide (just about the same as a size 10 or 12 hook):

Once the nymph decides the time is right to hatch into a Dun (this can be anytime between 1pm and 6pm) the nymph swims through the water column to the surface.

The nymph then transforms into the dun in open water and takes a few moments for its wings to unfold and dry out (it is at this point where it is able to fly). From the time the nymph arrives at the surface to when its wings dry out is the point that trout usually take them (either just below the surface or as they emerge), so don't be too quick to retrieve your fly if it should start to sink! You will also notice that when the trout takes the fly it will be a very splashy take, they know that the mayfly is one of the best meals of the year and need to make sure that they do not escape. I have even seen trout slash at hatching Mayflies just to disable them and then turn around to take it knowing it cannot escape.

Mayflies famously only live for one day. From the time they hatch, they will fly off to some local vegetation (the underside of tree leaves is a favourite spot, where they will rest (which can be for up to 24 hours) then transform again into a spinner (the sexually mature adult).

Once the adult mayfly is ready to mate they will form together in clouds above the river and dance (this is a stunning sight - when you are on a river in the early evening, just look up and watch them). Here the adults mate and the female will return to the water to lay her eggs (she can lay up to 10,000 eggs). Once the female has laid all her eggs, she will die and float away (this is called a spent mayfly).

From a fly fishing perspective the stages which we must try to imitate are:

  • Spinners
  • Duns
  • Nymphs
  • Spent Mayflies


The most popular imitations for emerging Mayflies are any of the flies below. Don't worry if you don't have these exact patterns, as anything which has the same general colour, profile and size will do. These flies should be fished as you would any other dry fly, and they should be used as soon as you start to see the Duns sailing down the river; this can be anytime from about 1pm until 6pm.

Top Tip: Only apply floatant to the hackle of the fly, this will make the rear sit just beneath the surface.

Mayfly Spinner

Mohican Mayfly

Loop-Wing Mayfly Dun

CdC Mayfly Dun


The Mayfly nymph is generally imitated by any of the standard mayfly nymph patterns (The Walker mayfly pattern is a favourite of ours). Take a look at these for some inspiration:

Spent Patterns

Once the female Mayfly has laid her eggs, she dies, these flies float down the river with their wings outstretched, and are easy for the trout to intercept. Due to the large number of Mayflies which hatch, there are usually lots which are malformed when they hatch, these are easy pickings for trout. Here's a fantastic pattern to imitate both the crippled and spent Mayflies:

Stillborn Mayfly

Image Sources

Mayfly Header Image: Courtesy of Ben Lupton (thanks Ben, you're a star)
Mayfly Lifecycle Image: Courtesy of Ben Lupton (thanks Ben, you're a star).


This email is brought to you with the sole intent to spread the information around so we can all maybe learn something. If you would like to buy any of the flies contained within this email, we do hope that you will consider us and see what flies we have to offer. If you would like any further details on any of the above flies, they can be found using these links:

Mayfly Spinner
Mohican Mayfly

Loop-Wing Mayfly Dun
CdC Mayfly Dun

Brown Mayfly Nymph
Olive Mayfly Nymph

Spent Mayfly:
Stillborn Mayfly

Previous issues of Hatch Chat can be found on our Hatch Chat blog, here: