It has been said that the hatch charts found in instructional books on fly fishing should come with a health warning, because Mother Nature is nothing like as tidy minded as we would like her to be. Influenced by a number of environmental factors, chiefly the weather, and by their own idiosyncrasies, insects do not observe the hatch charts quite as assiduously as we might wish.

River keepers will tell you they see almost every fly of interest to trout in almost every month of the year. The truth is, though, that occasional Mayflies hatching in October, or the odd blue-winged olive fluttering up from the surface in December, are curiosities – interesting but of little real consequence. It is very rare indeed that they appear in numbers sufficient to provoke a response from the fish.

Assuming that they happen at all, the species in question not having been wiped out by diffuse pollution and the like, most significant hatches of most insects are, in fact, reasonably predictable – some, of course, more so than others. I do not recall ever having seen a grannom after the end of April, a hawthorn fly much before or after the last week in April and the first in May, or a caperer much before the end of August.

Mayflies, in particular, are very largely creatures of habit. While the beginning and end of the hatch varies from river to river and even from fishery to fishery on the same river, the start of the local hatch can usually be forecast quite accurately to within a day or two. End dates can be more difficult to predict because hatches tend to peter out over a week or so, the trout losing interest gradually. (Incidentally, I have long since ceased to be excited by the sighting of occasional Mayflies a fortnight or more before the hatch proper is due. It happens every year and rarely, if ever, excites the trout, which almost always seem either oblivious to the giant flies or even a little nervous of them.)

All of this is a somewhat roundabout way of saying that the unreliability of hatch charts, such as it is, has more to do with the weather and, in May at least, the choice of flies available to trout than with inherent inaccuracy. The majority of hatches large enough to interest the fish do, in fact, occur in accordance with established hatch charts. But that does not mean that fishing hatch-matching flies will necessarily guarantee us heavy baskets.

Last year, I visited the little Hampshire chalkstream upon which I do most of my fishing three times between April 24 and May 2. On each occasion, so confident was I that an artificial Hawthorn would be the panacea of the day that I knotted one on when tackling up at the car before strolling down to the river. Sure enough, on each of those days, there were huge numbers of hawthorn flies, black as your hat and seemingly bigger, fatter and juicier than any I had seen before, bumbling about in vast swarms in the lee of almost every waterside bush and hedge.

Did I take fish on my Hawthorn pattern? Er, no. On not one of those visits did I see a single hawthorn fly on the water, nor did the fish show the slightest interest either in my own tying or in any of the two or three other Hawthorn patterns I dug out of my fly box. Instead, I took two fish on a Pheasant Tail & Hare’s Ear (PTHE) Nymph on April 24; three on a Parachute Adams and two on a PTHE Nymph on April 30; and two each on a Parachute Adams and a PTHE Nymph on May 2.

The reason for the Hawthorn’s failure, of course, was that the natural is a terrestrial which only ever arrives on the water by accident, born there on a sufficiently strong wind coming from the right direction – from our and the trout’s point of view, if not from the hawthorn’s. As it happened, breezes in late April and early May last year were remarkably light and the naturals, although notoriously inept fliers, were well able to hold their own against them and avoid being blown onto the river.

The choice of the Parachute Adams and the PTHE Nymph as alternatives to the Hawthorn at that time of year was easy. There is no grannom hatch on this particular river and the only aquatic flies that do appear fairly consistently throughout April are large dark olives (LDO), usually around the middle of the day. The Parachute Adams does a good impersonation of a variety of hatching up-winged flies, including the LDO, and the PTHE Nymph (or almost any similarly Pheasant Tail Nymph-like offering) will often take fish before and during hatches of LDO. In some areas, choice may be complicated slightly by the availability of the march brown or, perhaps, one or more species of stonefly. Generally, though, neither fish nor fisherman is confronted with complex choices in April.

Two or three weeks later, fly selection can become very much more difficult due entirely to an embarrassment of riches. Although up-winged fly populations are in serious decline on many rivers, more species can still be expected to appear at this time of year, and in greater numbers, than in any other month. Almost every fly species upon which trout feed hatches, or begins to hatch, during the last three weeks of May. Depending upon where you live or fish, medium olives, small spurwings, small dark olives, olive uprights, iron blues, pale wateries, caënis, black gnats, sand flies and stoneflies can all put in appearances alongside the mayflies, and identifying what the fish are feeding on can become quite a challenge.

The complexity can be compounded from mid-May to mid-June by our understandable preoccupation with the mayfly. So iconic has it become and so easily convinced are we by the term ‘duffer’s fortnight’ that we tend to suppose, albeit perhaps subconsciously, that it is the only thing trout feed on at this time of year. It is not. But I must confess to having been duped by this supposition myself on a number of occasions.

One of the most resoundingly blank days I have ever had – and I’ve had my share – came in the early 1980s, when fishing as a guest on the Wilton Club’s water on the lovely River Wylye in Wiltshire, right at the peak of the mayfly season. My host, who happened also to be my GP, was an experienced and skilful fly fisher.

Neither of us saw a single fly or a single fish rise during the morning, but at about three o’clock the Mayfly hatch began. Starting gradually, it quickly escalated into one of the most spectacular hatches either of us had ever seen, with every square foot of water accommodating at least one newly hatched dun, the air thick with swarms of the things heading unsteadily for the bankside herbage and trout rising everywhere. Two hours later, with the hatch continuing undiminished, clouds of spinners began to appear, dancing above the meadows before the females headed for the river to lay their eggs, die and add to the superabundance of food available to the presumably replete and burping fish. Not until dusk was enveloping the valley did the air begin to clear. Never before or since have I seen so massive a combined hatch of duns and fall of spinners.

Naturally, we were well prepared. As the hatch started, we went our separate ways, each of us armed with an assortment of favourite mayfly patterns and brimming with confidence.

By the time we met for a mug of tea and to compare notes, neither of us had touched a single fish despite the fact that we had tried just about every popular mayfly pattern as well as a few ‘funnies’ we had designed ourselves. The recalcitrance of the trout defied analysis. As far as we could see, they were taking mayfly duns and spinners in approximately equal numbers and in characteristic form, slashing at the duns to prevent escape and sipping down doomed spinners in a far more relaxed way.

We returned to the task in hand, flogging away until darkness drove us home, fishless, without even the satisfaction of having aroused the slightest interest in a single trout, and with memories of the day etched deep.

I don’t suppose we shall never know why we failed so dismally. The most likely answer is that the fish simply had so many natural flies to choose from that they dismissed our less than lifelike offerings with barely a glance. Some years later, though, I did come across a phenomenon, now quite widely recognised, that could just, perhaps, provide at least part of a less obvious answer.

Throughout the 1990’s and until a couple of years ago, I was privileged to have a rod at Abbotts Barton, the Itchen fishery made legendary by GEM Skues, who fished it from 1883 to 1938, and used it as the main laboratory for his development of the theory and practice of chalkstream Nymph fishing. When first I began to fish Abbotts Barton, no Mayfly hatch had been seen there since 1916. During the 1990’s, though, and possibly due to slightly reduced flow rates and a consequent increase in the sedimentation so beloved of Mayfly nymphs, an annual hatch developed – sparse and spasmodic to start with but becoming far more substantial and predictable as time went on. An unusual characteristic of it is that, while the hatch proper begins on about May 20, as do the majority of chalkstream Mayfly hatches, it continues for longer than most, not fading away until the last fortnight in June.

Roy Darlington, the prime mover behind the restoration of the fishery during the 1970’s and ‘80’s, watched development of the hatch closely and with great interest. He noticed that, rather than taking newly hatched duns, the fish frequently became preoccupied with discarded nymphal shucks, presumably because they made easier targets and, unlike duns, could not suddenly fly off.

Perhaps surprisingly, the shucks are actually quite rich in protein, making them a worthwhile component of a trout’s diet.

There is a clue here, of course, to the trout’s instinctive economy of effort – its natural preference for taking food forms that cannot escape or are unlikely to escape, rather than those that may avoid capture by flying off at any moment. There are countless examples, including the taking of emergers and spent spinners in preference to duns and, on stillwaters, taking huge numbers of midge pupae but very few hatched adult midges.

Following Roy’s discovery of this unexpected behaviour, several of us developed simple patterns to represent the shucks, and I have since used mine with considerable success at Abbotts Barton and elsewhere.

While preoccupation with nymphal shucks during a Mayfly hatch may fool those unaware of the phenomenon, far more of us are fooled far more often by trout that quite suddenly become wholly uninterested in Mayflies, no matter how many there may be on the water, focussing their attention on some other insect species. Black gnats and iron blue duns are the chief offenders, both featuring high on the list of the trout’s favourite foods, with medium olives and small spurwings being notable culprits, too.

On many occasions I have taken too long to realise that trout were not actually taking Mayfly duns sailing along on the current, but had instead become fixated on something much smaller and far less obvious. This has usually happened during relatively sparse Mayfly hatches in windy weather, when the Mayfly duns have been able to dry their wings quickly and get airborne in seconds.

Sadly, the iron blue dun is one of the aquatic insects that has been most seriously affected by whatever it is that has caused – and continues to cause – the dramatic decline in the fly life of British rivers. ‘Sadly’ because, apart from the Mayfly, there is really no other insect which brings fish to the surface so reliably on even the coldest, blusteriest days.

Black gnats, however, are, of course, terrestrial rather than aquatic and are still common on most rivers. I nearly said ‘commonly seen’, but one of the chief problems with black gnats is that they do not advertise their presence. Small and (obviously) matt black, they tend to blend with the background and to go largely unnoticed unless you are actively looking for them. And therein lies one of the clues as to why we may be so easily deceived, focussing our attention on big, elegant Mayflies, rather than on what the trout may actually be taking.

I tend to lump medium olives and small spurwings together because I would challenge anyone to differentiate between them with any certainty without a magnifying glass, and the trout are certainly not bothered by their minute differences.

As is the case with so much to do with fishing, the key to success is observation and experimentation. Just because there are some Mayflies on the water and the trout are rising freely, we should not suppose they are necessarily taking Mayflies. It is worth watching a rising trout very carefully, and watching the water ahead of its lie, to see whether it really is taking mayflies or something less obvious. A pair of pocket binoculars can be very helpful if it becomes clear that Mayfly duns or spinners are not the flavour of the moment. Discarded nymphal shucks float flush with the water’s surface or hang just beneath it. Black gnats can be very difficult to see against reeds or rushes, or against reflected bankside vegetation, from which they rarely stray far. And even iron blue duns, medium olives and small spurwings can be hard to spot against complex backgrounds, especially if the water is a bit choppy.

Finally, the wealth of insect life that should be available to trout from mid-May onwards holds one more trap for impatient fly fishers.

Mayfly hatches do not often begin much before mid-afternoon and falls of their spinners rarely occur before evening. It can be terribly tempting, though, to turn up and start fishing soon after breakfast, to risk catching one’s limit by lunch time, and then to find oneself a spectator at the Mayfly carnival or, worse still, having to traipse home to mow the lawn, walk the dog or get on with painting the kitchen. I did it myself on numerous occasions as an impetuous youth. Nowadays, I try to fill Mayfly mornings with other things, resisting the temptation to head for the river until later in the day.

Thorax Iron Blue Dun

  • Hook: Fine wire #16.
  • Silk: Black.
  • Tail: Black cock’s hackle fibres.
  • Tag: Red floss silk.
  • Body: Mole’s fur.
  • Hackle: Sparse black cock’s trimmed level with the hook point.Although iron blue dun hatches have become something of a rarity, there is no other insect that can excite the trout so certainly, even during a Mayfly hatch. It is difficult to over-emphasise the minuteness and delicacy of the natural, or to tie an artificial sparsely enough to represent it effectively.

Aw Shucks

  • Hook: Fine wire #12.
  • Silk: Buff.
  • Abdomen: Pale buff dry fly body yarn.
  • Thorax: Golden brown seal’s fur.
  • Hackle: Pale cream cock’s tied as parachute hackle.
  • Wing post: Pale buff dry fly body yarn.This is the pattern Peter Lapsley uses when trout appear to be feeding on mayflies’ nymphal shucks, rather than on duns or spinners. Because it is designed to lie flush in the surface film and can therefore be almost invisible, the wing post is a useful aid to tracking its progress.

PTHE Nymph

  • Hook: 14-18.
  • Tying silk: Brown.
  • Tail: Cock pheasant centre tail feather fibre points.
  • Abdomen: Cock pheasant tail feather fibres ribbed with fine, gold, oval tinsel.
  • Thorax: Six turns of fine lead wire covered with dubbed hare’s fur, picked out to form ‘legs’.
  • Wing case: Cock pheasant centre tail feather fibres.The Pheasant Tail & Hare’s Ear (PTHE) Nymph is one of several excellent general nymph patterns which can be useful during the lead-up to a hatch of large dark olives in April – or of almost any other olives during the rest of the season.

Parachute Adams

  • Hook: Fine wire #12-18.
  • Silk: Grey.
  • Tail: Grizzle cock’s hackle fibres.
  • Body: Grey muskrat or similar.
  • Hackles: One grizzle and one brown cock’s hackle.
  • Wing: White calf.

The Parachute Adams is one of the most reliable patterns for representing emerging large dark olives.

Hawthorn

  • Hook: Fine wire #14.
  • Silk: Black.
  • Body: Cock pheasant tail feather fibres dyed black.
  • Wings: Natural CdC.
  • Legs: Knotted black cock pheasant tail feather fibres.
  • Hackle: Black cock’s, sparse.

Having been blown onto the water’s surface, the natural hawthorn gradually subsides into it, which argues for the use of a non-buoyant body material supported a cul de canard (CdC) wing. The long, dangling hind-legs of the natural appear to be a key trigger point for trout.

Parachute Gnat

  • Hook: Fine wire #18.
  • Silk: Black.
  • Body: Black seal’s fur.
  • Hackle: Black cock’s tied as parachute hackle.
  • Wing post: White or yellow ethafoam or dry fly body yarn.The Parachute Black Gnat is a ‘speck of black’, and virtually invisible on the water. The white or yellow wing post is an essential aid to keeping track of it.

CdC Hare’s Ear Emerger

  • Hook: Fine wire #14-18. Silk: Brown.
  • Tail: Hare’s fur guard hairs.
  • Body: Hare’s fur guard hare’s ribbed with fine gold oval tinsel.
  • Wing: Natural CdC.
  • Legs: Hairs picked out from the thorax.The CdC Hare’s Ear Emerger is an excellent representation of the emerging duns of a wide range of up-winged flies. The body is designed to subside into the surface film where it is supported by the CdC wing.