Mayflies are aquatic insects that complete almost their entire life cycle under water.
They require clean cool water from which they obtain dissolved oxygen through feathery external gills that can be found on the sides of their bodies. Healthy quantities of aquatic plants are necessary for their food and shelter.
The wonderful thing about mayflies is that trout love to feed on them.
It is not essential to have a comprehensive knowledge of the different species to catch trout, but it is useful to have some knowledge of their habits, especially when a hatch is experienced or to be expected.
The takes are also spectacularly exciting as the trout rise and feed off the surface with an exploding splash.
At times the water can resemble a bubbling melting pot and the whole river/lake seems to come alive. Also the Mayfly conveniently start to hatch when the weather has started to warm up, the sun starts to shine and we have longer brighter days to enjoy the sport.
It is not such a great time for the Mayfly, having spent the last two years on the river or lake bed, snuggled down in gravel, sand or silt, it now struggles to the surface and if it's not eaten by a fish it will be dead within 24 hours anyway.
The family name for Mayfly is ephemeroptera (from the Latin ephemera which refers to its short life cycle and the ptera which is Greek for `things with wings').
There are three species within the UK: ephemera danica which is the most common type of Mayfly we get, ephemera vulgata which is also known as the Dark Mackerel because of the patterning on its wings, and ephemera lineata which is more than likely now extinct.
Mayflies or shadflies are insects belonging to the order Ephemeroptera (from the Greek εφημερος, ephemeros = "short-lived" (literally "lasting a day" "daily" or "day-long"), πτερον, pteron = "wing", referring to the brief lifespan of adults). They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies.
They are aquatic insects whose immature stage (called "naiad" or, colloquially, "nymph") usually lasts one year in fresh water. The adults are short-lived, from a few minutes to a few days, depending on the species.
About 2,500 species are known worldwide, including about 630 species in North America. The naiads live primarily in streams under rocks, decaying vegetation, or in the sediment. Few species live in lakes, but they are among the most prolific. For example, the emergence of one species of Hexagenia was recorded on Doppler weather radar along the shores of Lake Erie.
Most species feed on algae or diatoms, but a few species are predatory. The naiad stage may last from several months to several years, with a number of moults along the way. Most mayfly naiads are distinctive in having seven pairs of gills on the dorsum of the abdomen. In addition, most possess three long cerci or tails at the end of their bodies. Some species, notably in the genus Epeorus, have only two tails. In the last aquatic stage, dark wing pads are visible.
Developmentally, these insects are considered hemimetabolous. A more casual and familiar term is "incomplete metamorphosis". Mayflies are unique among insects in that they moult one more time after acquiring functional wings (this is also known as the alate stage); this last-but-one winged instar usually lives a very short time, often a matter of hours, and is known as a subimago or to fly fishermen as a dun. Mayflies in this stage are a favourite food of many fish, and many fishing flies are modelled to resemble them.
The lifespan of an adult mayfly is very short and varies depending on the species. The primary function of the adult is reproduction; the mouthparts are vestigial, and the digestive system is filled with air.
The wings are membranous, with extensive venation, and are held upright like those of a butterfly. The hind wings are much smaller than the forewings, and may be vestigial or absent. The second segment of the thorax, which bears the forewings, is enlarged, holding the main flight muscles.
Adults have short, flexible antennae, large compound eyes and three ocelli. In most species, the males' eyes are large and the front legs unusually long, for use in locating and grasping females during mid-air mating. In some species, all legs aside from the males' front legs are useless.
Uniquely among insects, mayflies possess paired genitalia, with the male having two penises and the female two gonopores. The abdomen is roughly cylindrical, with 10 segments and two long cerci at the tip.
Because of the short lifespan of the highly visible, winged adult form, the mayfly is called 'one-day' or 'one-day fly'.
Often, all the mayflies in a population mature at once (a hatch), and for a day or two in the spring or fall, mayflies will be everywhere, dancing around each other in large groups, or resting on every available surface.
The hatch of the giant mayfly Palingenia longicaua in mid-June on the Maros (Mureș) River and the Tisza River in Serbia and Hungary, known as "Tisza blooming", is a tourist attraction. In regions of New Guinea and Africa, mayflies are eaten when they emerge en masse.
The famous British chalk streams are probably best known for Mayfly hatches, these charming ephemerids are just as likely to thrive in less fertile rivers too. Loughs and lakes too provide an ideal habitat for the beloved Mayfly and if these are chalk or limestone based then so much the better.
Preferring silty areas, mayfly nymphs often reside in burrows. Measuring more than an inch in length on maturity, nymphs attain quite a size. Prior to hatching, like other up winged nymphs their wing buds darker considerably. With a long, sinuous body, three tails and feathery gills lining their abdomens these elegant nymphs are very distinctive. As ever, coloration depends on location though overall nymphs wear a creamy-yellow coat. If there’s still any doubt, dark brown markings on the upper abdomen are a dead giveaway and are most conspicuous on the three abdominal segments nearest the tail.
So if you get the chance and have some cracking imitates of a Mayfly in your fly box get out there and give it a go. Best times for a good hatch are from 11am onwards with a heightening activity usually between 3-4pm. Don’t forget to incorporate some spent spinners in your arsenal as well. Once the fish are tuned in and are aware of the Mayflies you will experience some fantastic sport.
Fly-fishing from a drifting boat is a great way to present the mayflies to a large number of trout.
A boat provides great mobility. Many trout will see your flies if the boat is handled correctly and bag limit catches are possible and not uncommon.
Fly-fishing from the shore or better still, wading or even float tubing, can also be rewarding and quite relaxing if you are fit and mobile, and good presentations can even the score a little. It depends also on factors such as your personal taste, your budget on where you can fish and the conditions of the day.
These are the four main groups to be found on the chalk streams during May:
There are three species (danica, vulgata and lineata) but treat them as one. All are so large you cannot mistake them for anything else!
Nymph Walkers Mayfly Nymph size 12
Dun Thomas‟s Mayfly 8-10
French Partridge 10-12
Grey Wulff 8-10
Spinner Spent Mayfly 10
Good for May, September and October. Likes to hatch on cold, wet, blustery days.
Iron Blue 16
Lunn‟s Particular 16
Pheasant Tail Nymph 16
Hawthorn & Black Gnat
Two closely related terrestrial species. Hawthorn at the start of the month, Black Gnats good for the whole month and summer.
Hawthorn 12- 14
Black Gnat 16-18