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Since i have had several enquiries about fly fishing entomology, i have decided to add this new page to my blog. It is not intended to be a professional opinion/study of anglers entomology. It is based on my observations of the fly life that i have encountered over the years when i have been out fly fishing on the many rivers and lakes of Ireland. It may be helpful to those that are new to the wonderful art that is Flyfishing. I intend to add further to this page as time goes on hopefuly building up a data base of the anglers fly life to a month by month chart of what flies an angler can expect to find. Bear with me if you will and i would appreciate any input and also feedback be it positive or not. It is also a learning curve for me.

Ephemeroptera : (upwinged flies)

Caenis :



The Caenis flies are the smallest of the Ephemeropterans. They are easy to recognise with their broad wings and three tails. There are up to six different flies in this group but they are all refered to as the Anglers Curse. They are widespread and like any type of water. The first hatches appear in June and continue up until September. Some hatch in the mornings and others hatch in the evening. They hatch in very big numbers which gets the attention of the trout.  Their small size makes them hard to imitate. I have never fished with a pattern for the Caenis fly.


Mayfly Ephemera danica

Mayfly Dun (Green Drake)

The largest of the upwinged flies is the most widely known and written about of all of the upwinged flies. It is often refered to as the Green Drake. The first hatches of the Mayfly usually appear in late May into early June. The hatches normally start about midday and continue on till evening. The female spinner is refered to as the Spent Gnat as it floats along dying after laying its eggs. It is also known as the Grey Drake while it is on the water during egg laying. Some good fishing can be had during a fall of male spinners.



From Dun to Spinner

Yellow May Dun (heptagenia sulphurea)

Yellow May Dun

The Yellow May Dun is one of the easiest flies to recognise with its bright yellow colour. It first starts to appear around the middle of May with the hatches continueing on into late July or so. The hatch starts mid morning with small numbers and the numbers increase as darkness begins. The rarely hatch in sufficient numbers for the trout to give them sole attention. The nymph of the Yellow May is also a stone clinger.

Yellow spinner

The Yellow May spinner returns in the evening to lay eggs. On a few evenings i have observed spinners in large numbers, enough for the trout to give them full attention even taking the hatching duns during the spinner fall.

The imitation i use for the Yellow May dun is a Tups indispensable. This i tie in a Klinkhammer style i find this also works during a fall of spinners.

Olive Upright (rhithrogena semicolorata)

Rhithrogena Semicolorata

The Olive upright is a fly which favours fast stony rivers and streams.They can also be found on some lowland rivers in broken water. Hatches of duns usually begin to occur about the end of April and peaking in June but can vary year on year. It is a fly which is very sensitive to water pollution. They generally start hatching from mid afternoon on into the evening. The nymph is the stone clinging type.

The spinner has yellowish wings is refered to as the Yellow upright. It has the ability to ascend vertically while in flight. Late in the day females can be seen crawling down vegatation to dip their abdomens in to the water to lay their eggs.

The imitation i use for the olive upright either the greenhammer (previous post) or a tups indispensable. The greenhammer is my first choice as i find it usually gets a better result.


Large Dark Olive (baetis rhodani)

baetis rhodani

The Large Dark Olive (LDO) is one of the earliest upwinged flies that you will see when you are river fishing. It first appears on the water in early March. Hatches usually begin from about noon up until mid afternoon. By the end of April or there abouts the hatches are starting to tail off. They may appear again in the Autumn on some of our rivers.

Spinner male

The imitation fly that i use when i see trout feeding on the hatching LDO is a Klinkhammer type. I call it a greenhammer because it is a Klinkhammer tied as per Greenwells Glory and finished off with an over body of fluorocarbon tied in touching turns covering the length of the body. If there are LDOs on the water and no signs of the trout taking them i then use either nymphs or a team of spiders i.e. Harelug & Plover, Waterhen Bloa and Olive Bloa. The spiders would be my first choice but if they dont work i then use the nymphs. The nymph of the LDO is termed as an agile darter and i would consider it worth while to carry an imitation. An olive nymph or a Gold Ribbed Hares Ear should are some of the imitations that i use.

So far i have not came across any spinners of the Large Dark Olive on the water and for the moment i cannot give any observations or comments on them.

Large Dark Olive

Trichoptera : (Sedges or Caddisflies)

Grey Flag ( Hydropsyche pellucidula/instabilis ):

Sedge (caddis fly)

The Grey Flag is a common sedge which is found where there is fast flowing water. It is one of the few sedges that will be seen during the day. They are often seen in small groups over bank side vegetation. The adults emerge in open water usually in the stretches after fast flowing pools. It is an important fly to the angler as the trout favour them as they emerge and also as the female is laying her eggs on the water. It is wise to carry a few different imitations with you. I use a Balloon Caddis as an emerger when ungreased as it sits just below the water surface. When i grease it i use it as an egg laying female. For me this particular pattern has accounted for many good trout.

Cinnamon Sedge (Limnephilus lunatis ):


The Cinnamon Sedge is a common species that occurs on almost all rivers/lakes. It is a slimly built sedge with wings of fourteen to sixteen milimeters long. Its colour can vary between rich yellow to a cinnamon brown with black markings. It makes a first appearance in June with sparse hatches continueing up to August. They often hatch throughout the day or early evening. A useful imitation that i carry with me is the Elk Hair Caddis.


Brown Silverhorn (Anthripsodes albifrons)

Brown Silverhorn

This small day time flying sedge can be seen on the sunnier days as it flies about in groups. It usually flies low to the water up and down the river keeping in to the bankside or flitting about under the trees. It first appears in June and continues to hatch up until August . Although the trout rarely become preoccupied with this sedge they will take some of them if the hit the water surface. Over the years i have observed some trout peform acrobatic stunts trying to catch this fly especialy when it is flying under the trees. I have had some success in catching fish when this fly is about in large numbers by fishing a small sedge dry by flicking it low under the trees when there are numbers of sedges flitting about.


Plecoptera : (Stoneflies)

The Yellow Sally (Isoperla grammatica)


With its yellowish green wings and yellow body this fly is easy to recognise. It is a medium sized fly which inhabits rivers and streams which have a gravely or stony bottom. The first hatches appear in April and continue on until August. Sometimes the name Yellow Sally gets confused with the Yellow May dun i.e. one been called the other. When i find this fly in decent numbers on the water the pattern i would use is the Yellow – legged bloa in a size fourteen. It is a simple spider pattern not unlike a Greenwell spider.When fishing a dry fly i use a Tups indispensible tied Klinkhammer style fished upstream. This i find gives good results.

Small Yellow Sally (Chloroperla torrentium)

Small Yellow Sally

The small Yellow Sally is common to mountain rivers tthat have a sandy or stony bottom. It first appears in April and is seen up until August. It is a small fly with a slim body ranging is size from five millimeters to eight millimeters. I use the same patterns as for the Yellow Sally but in smaller hook sizes (16s).


Small Browns (Nemoura cinera/picteli)

The small Brown Stonefly can be found in slow flowing rivers with plenty of vegetation and a soft/stony bottom. They are first seen in February and are still about in September. The adult fly is about ten millimeters in size. I have not yet came across big numbers of this particular fly so i cant vouch for any pattern to fish with.





Needle fly :

The Needle Fly is the smallest member of the Stoneflies. It is fairly widespread and it prefers fast flowing streams and river which have stony beds. It is similar in appearance to the Willow fly which are larger than ther Needle fly. It first appears in February through April and again in August through to the end of the season.

Needle Fly

Megaloptera :

Alder fly

Alder fly

The Alder fly is a well known and widely distributed fly which is found on almost any type of waters. It first appears in the early part of the season towards the end of April into May and June.It is Sedge like in appearance with its roof shaped wings when resting. It has a dark almost black head and legs, and its wings are similar to those of the Stoneflies shiny and hard. I have found the wet imitation works best for me with the exception of a couple of windy days that i used a dry sedge imitation when the Alders were being blown on to the water and the trout had tuned into them.

22 Responses to “Entomology”

  1. Colm says:

    Fantastic blog with a real feel for rivercraft and how everything works together. Love the photos and the entomology is fascinating. Hope you keep it up and keep catching and enjoying it this much.

  2. Alan says:

    Great read again , would it be possible to put a few pictures of fly patterns up? I would love to see if the flies I am using are the right ones for the job.

  3. wgsten says:

    At the moment i am working on getting a fly pattern step by step page together. I will post this a soon as it is ready.

  4. shane says:

    good site, just some constructive comments, As far as i am aware Ephemera vulgata has not ever been recorded in Ireland. Only in a few English rivers. Of course the common mayfly Ephemera dancia we have lots of them along the limestone basin.
    Caenis luctuosa (formerly known as C moesta) and Caenis horaria, are quite common in Irish lakes and Caenis rivulorum in some silty rivers. Caenis robusta has never been recorded in Ireland.
    you should add the lake olive Cloeon simile and some others too when you can.

  5. Peter Jackson says:

    Great site! Very interesting reading and good info on fly life. My son who lives in Delgany, Wicklow put me onto your blog today as he and and his two young sons also fish some of these rivers, particularly the Upper Liffey I believe.
    Good photography too; my son has asked me to tie up some flies (nymphs, dry’s etc) for him and the boys, so I now have a good idea what patterns to tie.
    As far as I know the description ‘Green Drake Mayfly’ can apply to either E.Vulgata or E.Danica.
    As a suggestion maybe to differentiate between the two when recording riverside sightings, we could adopt GDV for Vulgata and GDD for Danica? Just a thought.

  6. John says:

    Excellent informative read! I especially like the Fly Fishers Enotomology. I really look forward to more updates. Keep up the good work!

  7. wgsten says:

    Thanks John. I have a lot of material gathered for the entomology page. Many new fly photos which at the moment i am in the process of making proper IDs for.

  8. wgsten says:

    Hi Peter glad you like the site. I am working on a fly tying page which i will be adding to the site when i have it ready. I hope to include some of my own tying patterns as well as the more widely known ones on it.

  9. David says:

    Thanks wgsten. I studied this in detail in today. I think I might be catching my first trout on the fly soon thanks to this.

  10. adrian says:

    can you tell me what are the best flies to use when the river runs through boggy ground.???

  11. wgsten says:

    Hi Adrian, i have sent you a pm regarding your question.

  12. Patrick O Connor says:

    Great read, would love to see some pictures and details of the nymphs too


  13. wgsten says:

    @ Patrick O Connor. Thank you for the comment. I have had the idea of getting together photos of some of the nymphs that i have taken over the last few years and posting them along side the photos of the emerged duns and the Spinners of same insect. Hopefully i shall have some posted up in the near future.
    Tight Lines.

  14. Patrick O Connor says:

    Looking forward to it!!

  15. eoin says:

    Hi there
    Great site. It obvious a lot of time and effort went into the site. I have seen and read through a fair few fishing related sites in the last two years but yours is the most impressive to date. Could you advise on fly selection for local river as all I have tried to date have proved fruitless.


  16. wgsten says:

    Thanks Eoin. I have sent a pm regarding your querie.

  17. donal says:

    hi wgsten just got off your site pity other people that have your skill and expertise would not share witheveryone who want to know about fly life tying and fishing a great past time and the more experience we share with other fishermen and women the greater the knowledge we have about it just started to fish the lakes in the midlands whats the best flies to use and when thanks tightlines

  18. wgsten says:

    Thanks Donal.
    Here is just a brief summary of some of the flies i would use and when i would use them. Mid April you can expect to see the Duckfly appear in good numbers. You could try a Malard and Claret along with a Blae and Black in sizes 10s 12s. In early May the Lake Olive will make an appearance as will good hatches of the Alder fly depending on where you are fishing. A Sooty Olive works when the Lake Olives are there in numbers. An Alder imitation or a Black and Peacock spider should serve you well for the Alder fly. Size 12s. Sedges will be in good numbers towards the end of July and onwards. Try a Green Peter, an Invicta or a Bibio. One that works well for me a lot of the time is a Dabbler be it claret, pearly or a sooty. Sizes 10s 12s.
    Tight lines.

  19. Niall Murray says:

    Great work and a great read. Only getting started with fly fishing this year, you have given me a lot to consider, and glad to hear someone experienced taking (and needing) lessons.
    Keep up the good work, it will be my reference book on line.

  20. Keith walsh says:

    Hi great site any advice on what flies to use this time of year and going into August for trout on the river Lee cork. Again this is my first year fly fishing loving it.

  21. Chris Langton says:

    Fantastic Site !!
    A pleasure to read and to work from-
    Shows me how much more there is to learn
    Written by a ‘brother of the Angle ‘

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