The Evolution of the Bubble-butt Beetle by Ed Herbst

If you Google Philip Hills + Persistence Pays Off On the Smalblaar you will find a 2005 Piscator article on the website of the Cape Piscatorial Society which gives an indication of how even the most selective trout rarely ignore a properly-presented beetle pattern.

A growing body of research proves how important terrestrial insects are in trout diet, particularly on small freestone streams.

A beetle might provide as much nutrition as half a dozen nymphs.

The research of the late Shigeru Nakano, a Japanese scientist, showed that 77% of the daily prey intake of stream trout in summer was comprised of terrestrial insects and they provided 50% of annual food intake.

He built mesh-covered structures over trout streams so that light could penetrate but that the trout were deprived of their normal drop-in food. The fish population in the areas of the experiment quickly decreased.

My fascination with sunken beetles was the result of reading about their success in books like Mike Weaver’s 1991 classic on small stream fly fishing, The Pursuit of Wild Trout, but in the Western Cape beetles are only prolific in spring.

The realisation that there is one beetle species that is not seasonal came when Alan and Anabelle Hobson visited me in Cape Town last year en route to the Cape Getaway Show where they had a stand.

Alan and Annabelle Hobson at their stand during the Cape Getaway Show

Alan had come to the realisation that predaceous diving beetles are a constant food source for river trout and yellowfish in the Somerset East area where he runs a guiding business and, using his cellphone, showed me a comparison of these insects found in a yellowfish and the imitations he was tying.

Alan Hobson’s foam diving beetle imitations compared with the insects found in a yellowfish

In the interview with him in issue 9 of this magazine, he spoke of taking four days to complete an imitation of these aquatic beetles from shaping the foam with a Dremel tool to the final coat of Seal Skin with a six hour drying period between each step in the process.

He charges between R25 and R45 per pattern depending on its tying complexity but equivalent US patterns such as Chuck Kraft’s Excalibur on the Eastern Trophies website cost around $20 dollars which, at the current exchange rate is more than R250.

Alan has taken to adding a drop of fluorescent yellow Loon Hard Head cement to the top of these flies before the final coat of Seal Skin to make them easier to see.

They are proving to be exceptionally effective when casting to sighted yellowfish on the Sterkfontein and Vanderkloof Dams and trout in Somerset East. It is equally effective when tied to the bend of a nymph because the insect has to make periodic visits to the surface to replenish its air supply and its rise and fall behind a nymph when it is twitched exactly imitates this behaviour.

A Google Images search on ‘Predaceous Diving Beetle Air Bubble’ opened up a further avenue for exploration because that bubble is literally a bullseye for fish to target –  on what might justifiably be called a Bubble-butt Beetle.

A local diving beetle with its air supply –photo courtesy of Charles Griffiths

Air bubbles, looking like drops of mercury, are familiar prey images to fish such as trout – think of the air bubble trapped between the wings of the ovipositing baetis adult or the silver sheen surrounding an emerging blackfly adult.

In the 1990s Bill Black of the Spirit River Company sent Colorado guide Pat Dorsey some glass beads to experiment with. By far the most successful was the clear bead with a silvered centre and this led to his Mercury series of flies now marketed by Umqua.

Dorsey wrote: The following week, I took the Mercury Midge to the South Platte River in Cheesman Canyon and tested it rigorously. I was pleasantly surprised to see discriminating rainbows move 8 to 10 inches to intercept it. I knew there was something special about the bead that persuaded trout to eat this fly but I could not put my finger on it. Later it occurred to me that the silver-lined glass bead imitated the gas bubble that gets trapped in the midge’s thorax when it emerges.’

It occurred to me that I could use this idea to mimic a diving beetle by attaching a silver-centre or translucent glass bead to the bend of a hook with stainless steel wire and then tying a conventional sunken beetle forward of the bead.

For the shellback I used Jan Siman Pearlescent Shrimp Foil, coloured brown with a permanent marker on the #14 beetle shown here. Mottled rubber legs provide movement and a Hareline 2 mm brass Dazzle Bead in mottled brown tips the beetle forward as though it was descending after replenishing its air supply. I used Quick Descent Dub for the body. It’s made of aluminium shavings and I have not come across a dubbing material which is easier to use.

The author’s prototype diving beetle with a silver bead imitating the air bubble

Alan has now incorporated the silvered bead in some of his floating beetle patterns and I must say my prototype looks primitive in comparison.

Alan Hobson’s versions of the Bubble-Butt predacious diving beetle

I regard Alan as one of the most innovative fly tyers in South Africa and his patterns are now being used with success all over the world.  Read ‘Alan and Anabelle Hobson – a Profile’ on Tom Sutcliffe’s website which also has several other articles on the outstanding variety of angling which the Karoo provides for trout, bass, yellowfish and barbel.

Visit the ‘Wild Fly Fishing in the Karoo’ and ‘Angler and Antelope Guest House’ for more information.