Steve Dunn grapples with a small insect that has a big angling impact.

It was a cool November evening on Lake Eucumbene with a light nor’ westerly breeze. I was fishing the flats opposite Providence Portal. I’d fished several hours from the boat, giving a variety of wets a workout in teams, and the fishing hadn’t been too bad. As is my habit, when the sun dipped over the mountains to the west, I quietly went ashore. I love boat fishing, but I really love bank fishing to the unpredictable Eucumbene evening rise. As the light dims, the trout can throw caution to the wind and cruise into the shallows, feeding opportunistically. You can wade 10 paces off the bank and have as many fish feeding behind you as in front of you. Occasionally, we’ll get termites or midge in such quantities that the fish start that focused-feeding where nothing else will do. Balls of dusty grey midge or sweet little termites being systematically and calmly mopped up one after the other. At times, it seems these fish will turn away from anything that isn’t just the right fly.

That evening, the trout weren’t feeding on the surface. But at frequent intervals, the water surface was boiling – a very distinct vertical water movement, but with nothing breaking the surface. When I’ve seen stick caddis in the water, and in the absence of any obvious alternative (like maybe a mudeye migration) I call these ‘caddis boils’.

So, on Providence Flats, on a nice buggy evening with plenty of boils but no single rise to a surface insect, I automatically reached for my selection of well-worn stick caddis flies, selected two different patterns, tied them 18 inches apart, and contemplated landing one or two nice rainbows in short succession, or maybe a good brownie. Twenty minutes later, and not a touch, despite seeing several more boils. I was fishing a long leader, the fly was sinking well, I’d mixed up my retrieves, and panic was setting in. So I resorted to a tried and tested practice and called upon my many years of close observation of angling mates, and asked, what would they do?

Somewhere in my deep memory an image sprung to mind of a friend fishing a stick caddis, suspended under a Claret Carrot dry. It took just seconds to change the rig and put my best stick under a big Carrot and get it back into the water. Success was almost instantaneous.

Roll the years forward a decade and we’re in November on a drought-impacted Lake Eucumbene with the water at around 20%. To say the fishing reports and my personal experiences were less than glowing would not be an exaggeration. Then, the catch-cry goes up, ‘Stick caddis!’ and there are reports of the best bank fishing for years from die-hard visitors. But then, a mysterious question, a conundrum. A question none of the gurus can answer. Why, mid-way through his annual fishing trip, did a reliable source report the stick caddis had changed colour from green to brown? And then, from the other end of the lake one, of my ‘Steve’ mates reported the fish had gone off green! Unheard of. The emails and texts flew around, social media posed the question and we even resorted to the telephone to actually talk about it, but no one could come up with a definitive answer.

So I said to Editor Weigall, “I’ll crack this nut, and I’ll write an article about it. I’ll find out why stick caddis change colour!” Several hours of diligent research later and I was more confused than ever. When some months later, Phil eventually and politely asked for my manuscript, I told him this particular topic was like a stone in my shoe – I knew it was there, I just couldn’t get it out. Unsympathetic and unmoved, he responded with a firm deadline.

What I know

From personal observation, the larval stage of at least some of the caddis fly species we have in the Snowy Mountain lakes looks like a small stick. That stick-like structure contains a grub. The stick caddis is part of the aquatic phase of the caddis fly lifecycle – the bit between egg and pupa. Look for them and you will see these sticks in clear water close to shore. Look really closely and you will see the little grub peeping out of the top. They seem to have some means of regulating buoyancy so they can bob along midwater. They can certainly swim, albeit quite awkwardly, so at times they move a little bit faster than the other things in the water – or sometimes are stationary whilst other things move. The ‘stick’ is normally a bit thicker at one end than the other, and they are usually more vertical than horizontal in the water, thick end up. If you catch one, the grub will retreat well into the stick and you can pinch off a bit of the top of the case and the grub will pop out before retreating further inside the case.

Frequently, the ‘stick’ isn’t actually a stick or piece of reed, it’s a constructed hollow tube. Whereas some stream-dwelling caddis species make larval cases from tiny pieces of sand held together with a gluey substance that comes from the larva, other species use bits of aquatic vegetation and detritus to construct a stick ‘case’; while still others take the lazy option and use a hollow piece of reed or stick!

In the Snowy Mountains lakes, the most obvious stick caddis resemble a tapered mini cigar with a stick which looks like it’s a leaf rolled in a uniform spiral. They are usually between 10 to 20 mm long, and 2 to 3 mm in diameter. ‘Sticks’ can be black, green or brown depending on the material used. The larva can be a wide range of colours from a creamy white to pale green, sometimes looking a little fluorescent, and with a very small black head. Put caddis larva in a tank with gold leaf or particles of precious stones and you will get a golden-jewelled stick caddis, maybe that perfect gift for your non-fishing partner?

Going beyond personal observation, caddis are flies, not moths. They are found all over the world. The class that caddis flies belong to is Insecta. The order is Trichoptera. There are 47 families, about 610 genera, and more than 13,500 known species that have been described[1]. In the UK they are called sedges; in other parts of the world rail-flies. If you want to do more research, the family the main Snowy Mountains lake caddis species belong to is Leptoceridae.

The adults are usually seen flying around in very large numbers right on dark. Literally one minute there are none; then there are millions. At times they can be so dense, they get in your mouth and eyes and crawl down your shirt. The adult caddis around the lake are mostly brown; while on the Eucumbene and Murrumbidgee river systems, it is very common to see the perfect white snowflake caddis, especially around the streamside tea-tree bushes. Adult caddis flies are not there every night; they definitely have mass mating events.

Of special interest, the late John Sautelle’s book ‘Fishing for the Educated Trout’, contains fascinating information from NSW Fisheries’ Bob Faragher on the diet of Lake Eucumbene trout. Although it’s from research from back in the 1970s, over several years, caddis larva always showed up as a measurable part of the diet of Eucumbene rainbows and browns, and as much as 15% of the diet of rainbows in winter. No wonder Eucumbene anglers have always been interested in stick caddis.

The caddis lifecycle

The flying adults don’t live long and don’t feed – they don’t have a real mouth, and so can’t bite. The species we see as stick caddis in the lakes mate in flight and drop their eggs on the surface of the water. The eggs hatch within a few days to four weeks. Water temperature is a key factor.

Once hatched, the larva creates or occupies its case (the stick). Larvae feed by grazing algae off rocks; chewing, scraping or shredding vegetation; and by preying on other insects – they are not very mobile, but presumably they intercept things in the water column that are even less so. As the grub grows, it moults between 5 and 7 times.

The final aquatic part of the lifecycle is the pupal stage, the transformation from larva to adult.

What I don’t know

There is so much I don’t know. I don’t even know the species, but I am certain there are more than one in Lake Eucumbene. Under rocks, I have found very different-looking caddis cases, circular and made up of small grains of sand, that I suspect are the family Helicopsychidae. I don’t know how sensitive the larval development is to water temperature, but I certainly don’t see the adults in winter. In fact, on the Snowy lakes, I have only seen the really big adult flights in the warmer months.

I don’t know much about the pupal stage. In some places outside the Snowy Lakes, the vigorous swimming of caddis pupa to the surface is a fishing event in its own right, resulting in explosive rise forms. Here on the Snowy Mountains lakes though, I’ve never knowingly witnessed a pupa emergence, so I have my suspicions that here, they’re slower and less conspicuous. It does seem as if the mass mating/ egg-laying flights of the adults are synchronised, though not entirely predictable. Some evenings there are so many you have to keep your mouth closed; the next there might be none. Calm evenings after rain seem popular, but that’s just a casual observation. Really cold weather seems to stop the flights and if a lake drops quickly, it certainly slows them down.

Back to the fishing.

So, stick caddis (the larva) seem to be the main event and fortunately, on the Snowy lakes, this stage is common and long-lasting. “Anything small and green will do the trick when the caddis are about,” said one of my fishing mentors when we were discussing this recently. Over the years, my favourite green fly has changed from a damsel, to a Tom Jones, to small Woolly Buggers, to green nymphs, with the emphasis always on small – size 14 or smaller, and lightly dressed and slowly retrieved, and I am completely content with the idea that these are taken for a drifting stick caddis. And of course actual stick caddis imitations work very well.

Although I said earlier that the adults are less important fishing-wise on the Snowy Lakes than the larva, after mass flights, there are sometimes a lot of dead caddis on the water and trout seem to mop these up on windward shores right through into the next morning. I once had a particularly good early morning session with our Editor, boat fishing a slick of dead caddis on Tumut Pondage. There are a lot of English patterns used to fish for trout feeding on dead caddis like Wickham’s Fancy, Mallard and Claret, Green Peter, Peter Ross (the first fly I caught a trout on), and Invicta patterns. But in Australia we seem to prefer elk hair patterns and the Antron Caddis – which are among my top ten magic pudding patterns of the last decade.

And back to the green and brown question. I think this is simple. The case matter is aquatic vegetation. In warm water, close to shore, the vegetation will start to decompose, the chlorophyll will break down, the green colour will disappear, and the darker colours result. With intermittent mass mating events, you get a pulse of sticks; a single cohort that grows over several weeks. And their houses simply change colour depending on the available building material.

As a final qualifier, I acknowledge there is more I don’t know about Snowy Lakes caddis than I do know. Besides the Bob Faragher reference earlier, I could not find one scientific reference to caddis on Lake Eucumbene or any other Snowy Mountains lake. If anyone can add to or correct the story, I will happily update it!

For more information on fishing caddis generally, look at Stewart Dick’s article ‘Caddis – What I wish I’d known‘.

And thanks to the Murray Darling Freshwater Research Centre bug guide which you can pick your way through at your leisure.

[1] Morse JC. The Trichoptera world checklist. Zoosymposia. 2011;5:372–380