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The size of it

By Dave Southall

Dave Southall says there are times when choice of fly-size can be crucial, and gives his two tiny flies with a big reputation - the Bead-head Pheasant Tail Pupa and the Hackle-less Black Gnat.



  • Bead-head Pheasant Tail Buzzer Pupa

    Bead-head Pheasant Tail Buzzer Pupa

    Hook: Tiemco 2488, size 20 to 24.
    Thread: Brown or black 8/0.
    Head: 2.0 and 1.5mm black brass or glass beads.
    Abdomen: Cock pheasant tail fibres ribbed with either copper wire or fine gold holographic tinsel.
    Thorax: Black hare’s ear tip dubbing.

  • Hackle-less Black Gnat

    Hackle-less Black Gnat

    Hook: Tiemco 103BL, size 21; Orvis 4641 Large Eye Straight Eye Dry Fly, size 20 to 26.
    Thread: Black 8/0 (waxed).
    Wings: White Tiemco Aero Dry Wing or siliconised polypropylene yarn.
    Abdomen: Tying thread.
    Thorax and legs: Black standard SLF dubbing.


In my article which was published in the January 2009 issue of FF&FT, (Coloured by experience) I mentioned that there may be one or more triggers which stimulate trout and grayling into taking our flies. The second trigger which I’d like to consider is size. Often, when the fish are not preoccupied with specific food items, the exact size and choice of fly is relatively unimportant. Trout are opportunistic feeders. One only has to look at the stomach contents of the average trout to see this. Last season I caught a brown trout with a large bullhead still protruding from its mouth. On examining its gut contents I found several small black beetles, a couple of Baetis nymphs, a few large dark olive duns and a hawthorn fly.

However, there are times when the fish may be totally preoccupied with one food item. This most often occurs when there is an abundance of tiny invertebrates available. At such times it can be essential to use flies which are – as near as is practical – the same size as the food source, the fish being unable to associate anything bigger with food. Fish have very small brains and therefore seem incapable of processing too much information at once. As a result they can develop a very simplified 'food image' when certain foods are abundant. This innate adaptation makes them more energy efficient feeders.

This 'one track mindedness' is also why fish which are mad on feed are surprisingly difficult to scare and why spawning fish seem completely oblivious to any other stimuli. Even I, with a far superior brain, find multi-tasking difficult!

So when might we expect this preoccupied, size dependent, feeding to occur? Any time of the year is the answer. Much depends on where you fish.

On my local small stillwaters we get hatches of tiny micro-midges every month of the year. The adults look like specks of soot drifting on the surface, whilst the pupae are like commas on a piece of newsprint. A realistic imitation would be tied on a size 36 hook (if you could get one).

When I see the typical head and shoulder rise-form of midge feeders I usually start with size 20s tied to 5x tippet in the hope that the fish aren’t too preoccupied and drop to size 26s to 6x tippet if I get too many refusals. I’ve even been known to resort to size 30s. Going too light is a problem, since I hate protracted playing of sizeable fish with the attendant risk of lactic acid build up in their muscles and subsequent death if not thoroughly nursed back from exhaustion. A size 26 fly on 6x tippet is a compromise between adequate presentation and protracted landing time (7x or 8x would give far better presentation).

Recently, I’ve been trying a loop knot (right) for attaching the fly. This permits much freer movement than a fixed knot with relatively stiff tippet. I’ve not had time to evaluate it yet, but am quite confident that it will improve my presentation of such small flies. Jesper Larsson who guides at Rajaama Fish Camp in northern Sweden showed me the knot and swears by it for reducing micro-drag when fishing dry flies in turbulent flows. It certainly worked well for me using larger flies when I visited Rajaama with the FF&FT trip in August 2007. Patterns need to be kept simple for tiny flies. For the adult midges I use either a CdC IOBO Humpy (see December 2007 issue) or a Hackle-less Black Gnat. For the pupae I use either a Black Bead-head Pheasant Tail Buzzer of my own design or a Sawyer Pheasant Tail Nymph.

Micro-midges are also a significant food source on most rivers. With global warming, siltation, abstraction which reduces flows, and the decline in upwinged flies they are becoming more so year by year. Grayling, in particular, can become besotted with them to the exclusion of all else. Here again, a simple size 24 to 30 dry fly may be all they will look at, provided it is well presented (micro-drag free).

In late July and early August thrips or thunder bugs can blow onto the waters near to cereal crops. Once again a size 26 to 30 thin-bodied IOBO Humpy or Hackle-less Black Gnat is the answer. A couple of years back, on the Yorkshire Rye, during a hatch of small dark olives, I was having a frustrating time; trout were inspecting, but refusing, my size 18 Parachute Olive. It was not until I noticed the thunder bugs on the water and changed to a size 24 IOBO Humpy that I was rewarded with slow, confident rises from both trout and grayling.

On both rivers and stillwaters dawn and dusk throughout the summer can see massive hatches of tiny Caenis (the Fisherman’s Curse). Early in the hatch the fish mainly take the nymphs since the duns seem to explode out of the shuck, never resting on the surface. However the duns soon transpose into spinners, which mate, egg-lay and die within half an hour. It is then that the surface can be plastered with tens of thousands of prostrate corpses. You might stand a chance with a size 22 spinner, but as mentioned in my article on presentation (see FF&FT, December 2007), a dragged size 20 Griffiths Gnat seems to provide an added trigger, stimulating the fish to select the artificial from the plethora of prostrate spent spinners.

Rising like metronomes
In late spring and autumn, aphids are often at their peak of availability. Strong winds in late April and early May dislodge these prolific insects, whilst leaf-fall in autumn often deposits vast numbers on the water. Yet again, I call on a size 24 to 26 IOBO Humpy tied with natural grey CdC (colour seems to be unimportant).

The iron blue is another small fly, which although sadly in decline is a favourite of trout and grayling. I don’t know why nearly all the commercially produced Iron Blue imitations are size 16 because the flies I see on the water are more like size 20. Towards the end of the 2007 trout season I had an invite to fish Foston Beck, a lovely little northern chalkstream. There was a good hatch of assorted olives and the fish were rising like metronomes. I tied on a size 16 Paraloop Olive, no response! A size 16 CDC Gasparin Dun, no response! A size 16 IOBO Humpy, still no response! Frustration was setting in: the hatch might be short-lived and I was missing out! I was getting close to using un-Parliamentary language when I noticed, mixed in with the olives, a few iron blues. A change to a size 21 CDC Gasparin Dun and later a size 21 IOBO Humpy resolved the problem. The result: 16 fine trout landed in a little over an hour, after which the hatch ceased.

This Tay brownie moved to a size 10 F-Fly fished prospectively when nothing was moving at the surface, but the occasional adult

When is a big fly necessary to trigger a feeding response? On my local Yorkshire Derwent I am restricted to the dry fly during June, July and August: when there is no hatch and the fish are loath to surface feed, a big fly like a Daddy or large sedge will often prompt a rise. I don’t for a moment credit the trout with the conscious thought “that’s big enough to be worth the effort”; it’s all too easy to anthropomorphise, giving the fish powers of reasoning. I believe that the size and the relatively splashy landing of such big flies provide strong enough triggers to induce the reflex feeding response. Last June I had some great fish from the Tay at Aberfeldy, in the middle of the day, when nothing seemed to be moving, by fishing a size 10 F-Fly to simulate the isolated large stoneflies which I saw. The response of the fish was explosive. In August, in Swedish Lapland, despite virtually no rising fish, the grayling would take a large Klinkhåmer or sedge with gusto: the dry fly well out fished nymphs and bugs.

So next time you’re failing to get takes to your fly, consider size: it may be a significant factor. In particular, don’t be scared to try really small flies: the fish can see them. If you use Orvis 4641 Big Eye hooks they are not hard to tie on. If you keep the patterns simple and use a lens they’re not difficult to tie. They are surprisingly good hookers and holders of fish.


This quality, small-stillwater rainbow was taken on a size 24 Buzzer.

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