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Autumn, and on many of our reservoirs and lakes, trout are eagerly hunting the margins. Whilst fry are often high on the priority list as a food source, often it is the Corixa, the diving water beetle that lives in weed-beds, that fish will chase and harry as they strive to pile on the weight for the oncoming spawning excesses and winter fast.
Corixa have always proved a fly-tying challenge. Skitting from its weedy hideouts on the lake bottom it flits to the surface using its paddle-like legs to cling to the surface and gather and then carry a bubble of air under its belly, before returning to the weedy depths.

The silvery gas-bubble of air has always been seen as a key trigger in the attration of trout to a Corixa imitation, as has the fast, jerky sink-and-draw action of its travels within the water column, but the paddle-like legs? That’s a different matter. How do you make a fly that swims with the same furious, rhythmical kicking action of Olympic champion, Michael Phelps?

That was the problem I set out to crack, and the principle of aerodynamics as used in aeroplane propellors helped solved it for me. That, plus a piece of polythene tube, some 30lb BS nylon, and some flat-nosed pliers, of course!
The resultant fly possesses weight for diving down, a silvery underbody to suggest the gas bubble at the belly, the correct coloration of the insect itself, and paddles that kick ten-to-the-dozen as the fly is retrieved through the water. Now we have a Corixa with colour, shape, flash and movement – what trout could resist this as it scours the weed-beds for crunchy water boatman snacks?

Road Runner Corixa

Hook: Kamasan B100 size 10 or 12.
Thread: Cream or white 8/0 Uni, light cahill 8/0.
Under-body: 2 lengths of round lead wire; 2 lengths of self-adhesive flat lead, cut into fine strips.
Paddle spindle: 3mm length of micro-tubing, cut square-ended with a razor blade.
Body: 4 strands of cream or white Lureflash Twinkle, coated in Epoxy resin.
Colouring: Olive green and black permanent marker pens.
Paddles: Length of clear 30lb BS nylon monofilament.

Other materials: Black varnish; Floo Gloo or Dave’s Flexament.

• Find out how Graham ties this fly in the October issue of FF&FT.

Water boatman, or Corixa. Note the long legs which it uses as ‘oars’ to propel itself through the water column.

The Road Runner Corixa in the vice. When you blow on it from the front the paddles should spin round, like propellors.

The Road Runner Corixa with paddles in position.