Caddis contrasts and conundrums

The gaping hole in the UK's knowledge of sedges in comparison to the US is exposed by Oliver Edwards.

My own experiences with the Sparkle Pupa were obviously quite different to Gary LaFontaine's, and, stupidly, I wondered if American caddisflies behaved quite differently to ours! Then one day, with my nose in the book again, it dawned on me why I'd failed so miserably with his patterns. Gary's observations of the behaviour of emerging caddis pupae, his hundreds of hours up close to them in scuba gear, were all carried out in daylight. My experiences with our major co-ordinated summer emergence of hydropsychids was always a late dusk event, when light levels were virtually nil. So, where I asked myself, does this now put Gary's glistening light reflective gas bubble? This was surely the reason why I had failed with the patterns, the effect must be nullified, you can't have reflected light if there is no light, can you? Tri-lobal Antron surely will not glisten if it's almost totally dark. Or was I missing something scientifically beyond me?

Several years later, out of the blue, our section of the Wharfe became populated with grannom in huge numbers – like a snowstorm. At last we had a caddis with a super co-ordinated hatch – during daylight. What immediately became apparent to me was the dwell time on the surface as the hanging pupae struggled out of their shucks. You could watch them drift past inches away. When you got your eye in you could also spot them in midstream – little dark humps on the surface, which suddenly appeared to pop, and, hey presto, an adult. I am always surprised how many of these helpless hanging strugglers are left unmolested, yet as soon as they pop, and the winged adult sits serenely, drifting high and dry, they nearly always get downed, and, if they start hopping and skipping about, they are definitely fish food … in a trice! I did a few complete autopsies in those first grannom years, and the results also confirmed what I'd been seeing; significantly more winged adults than both ascending pupae and emerging ones. However, the autopsies did show that a decent amount of the hanging emergers had also been taken. So now with this big daytime hatch I had a perfect opportunity to try once more the Sparkle Emergent Pupa. I tied some size 14 grey and brown ones. They looked a touch large so I also did some 16s. The grannom is quite small and the males are significantly smaller than the females. Also, this pattern does give an impression of bulk.

Well, I scored with them. But to be fair, the Sparkle Pupa didn't perform nearly as well as a small dry dark Elk Hair. This, and my other grannom favourite – a sort of shaped up 'F' fly with a very short fibred grizzle hackle palmered up the body did most of the damage. So, yet more doubting.

Over many seasons I've tried a variety of patterns to cover the various hatch phases of caddisflies but, apart from dries for the grannom, I've always been strongly inclined to fish my pupa pattern actively to copy the fast-swimming ascending pupa. This I usually fish in tandem with my P.O.P.A. caddis about 3ft away on a dropper. Fishing the pupa actively, according to Gary, will give only mediocre results, but it doesn't, it gives very exciting sport while the emergence lasts.

Gary LaFontaine informs us that there are three phases in a typical caddis emergence. The first is when the pupae cuts itself free from the cocoon then drifts along hugging the bottom current. This passive drift phases can be up to 20ft. The second phase follows when the pupa, having now generated the shuck-separating gas, starts to swim to the surface. Phase three is when the pupa has made it to the surface and hangs there on the underside of the meniscus – again passive – as it readies itself for splitting out and emerging.

Gary states that the two inert (passive) phases – the bottom and top drift – are the ones that trout concentrate on "almost exclusively" He also states that trout very rarely pursue the ascending pupa – the active phase. My experiences, always at dusk remember, runs contrary to this. I always fish my pupa actively, the only time it is not being actively swum is the short dwell I give it after hitting the surface, and allowing it to sink. When a hatch is underway, when hydropsyche caddis are running up and down your arms, settling on your face and glasses, the surface activity can unnerve you, with big fish making violent rises – as big as a bucket! I've tried the bottom dead drift before all this starts, many many times, but it has rarely worked for me. However, as soon as the pupae start shooting up to the surface, it's like throwing a switch: the fish are on them immediately, and, yet again, I miss last orders at the pub!

These fish – mostly trout but also some grayling – are definitely surging up after the swimming ascending pupa. The rise form is far too aggressive for it to be fish mopping up drifting, passive emergers. Furthermore, I've proved it is swimmers they're taking. Several times I've pumped random fish taken during these hectic spells and I've only found swimming pupae, some having been so very recently eaten they were still alive and rowing!

I've thought about the gas sheath or gas layer – the shiny appearance of ascending caddis pupa – many times and wondered if Gary LaFontaine got himself somewhat sidetracked by his discovery. Did it blinker him from other aspects of the caddis pupae? Behaviour, for instance? He didn't make much of an attempt at copying the swimming legs, just a few swept-back soft hackle fibres. Yet the long outstretched centre pair of legs on the natural are a huge trigger, especially when vigorously rowing. My own pattern's effectiveness stepped up a gear when I tweaked it by adding one or two pairs of rubber legs in place of the cranked and lacquered pheasant tail legs. (For anyone who has never seen a swimming caddis pupae, think water boatman or Corixa. The pupa's centre pair of legs is widened along the trailing edge of the lower leg section (tibia/tarsus) by a continuous hair fringe making it a perfect oar. They row in perfect unison quite rapidly, which scoots it along at a fair old lick. The first time you see one swimming you'll swear blind that it's a big Corixa.)

The other very pronounced anatomical feature of a ripe pupa is the pair of drooping, side-bulging, dark wing pads. Gary omits them on both his patterns, yet it seems to me that these are distinct enough to class as a secondary trigger.

I'm not quite sure now what to believe about the shiny gas bubble theory. I'm not even sure in my heart of hearts that it totally overrides the importance of other aspects of the live pupa, and I've become very sceptical that we fly tyers can get near copying it satisfactorily with today's materials. Maybe some day something will come along. However, I'm very sure that I have great, yawning gaps in my knowledge of caddisflies. From what I hear on riverbanks, shows, events and demonstrations, I'm not on my own! Yes, I've got plenty of books on the subject and the identification keys, which in the case of the adults, is mind-blowing – just page after page of genitalia! But to date, my books with the most in-depth information slanted towards fly-fishing hail from the US, and written for their hatches of course, which makes me bloody envious.

We need a good, thick book written by a professional entomologist who is a Trichoptera specialist, but he must also be an experience fly fishing nutcase.