If dragonfly nymphs are the aquatic insects king of lakes, then Dobson fly larvae are kings of the stream. Funnily enough, that’s not where I first came across them.

I was fishing at a high mountain dam in the Western Cape with my friend Nick Garrett, sadly I don’t have access to it any more. It was a special place and a little tricky to fish because you had to pull your float tubes up the high concrete dam wall to get to the water. You couldn’t fish from the bank because it was surrounded by steep sides with thick fynbos and at certain times of the year proteas would be in blossom hanging over the water as we paddled by in our tubes.

The best part was that the inlet was a gushing freestone stream on the far end of the dam and we would get out of our tubes and spot good sized rainbows holding in the long inlet and guide each other into fish. The crystal clear water made it easy to spot the fish and seeing how they’d react to the fly made for exciting fishing.

One day, Nick was fishing a big woolly bugger tied with this newly acquired multicoloured, red, orange and brown chenille and he was hammering the fish, and big ones too compared to my big zero. His chuckles as he leant back into another fish, which I normally love to hear, were starting to get monotonous and, of course, I asked to see his fly.

We paddled up to the inlet stream and I scrambled a bit on the freestone rocks as I climbed out of my tube and saw this huge centipede thing grabbing onto my leg. I might have screamed because centipedes gave me the creeps. But then it started swimming around flicking its tail like a shrimp or crayfish. I saw a few more and managed to catch one in my net and was amazed at its size, its strong looking jaws and its strong red/orange/brown colouring.

‘Hang on,’ I thought as the penny began to drop. I asked to see Nick’s fly again. Little did I know that an obsession had begun.

So what are they? The nymphs which are of most interest to the fly angler are also known as Hellgrammites, and it’s unknown where this name comes from. The adults are called Dobson Flies and are of the family Megaloptera, which comes from the Greek Megalo (large) Ptera (wings).

The larvae live in streams and sometimes build burrows and sit in wait between rocks with the jaws open waiting for a passing insect. I would imagine mayflies are pretty high on their diet.

Found in the USA, Canada, Asia and South Africa, the adults are the biggest aquatic insects in the world, excluding butterflies and moths. In the USA they have a wing span of 18cm and in Asia up to 21cm.

They don’t grow that big in South Africa and I have come across them on the odd occasion on our streams. They are quite delicate and soft and fly quite badly. I don’t think they are of a big significance to our trout but it does make you wonder when your huge early season dry gets smashed so readily.

I was lucky enough to come across a female laying her eggs on the side of a rock midstream. If you look carefully at the video below, you can see a number of older egg patches.

I have tried different methods of trying to imitate the hellgrammite, tying smaller patterns for trout and bigger ones for smallmouth bass. I’ve even got a solid eat from a carp close to an inlet. In the US they are a very popular pattern for large trout and bass, but their ones are dark browns and black mainly.

One thing that I have moved on from is tying intricate, time-consuming patterns that get snagged. I want flies that are easily bounced along the bottom of freestone streams. A glass bead version which is quick to . . . .  assemble, has been working well for me lately.

I’m not saying I’m smashing fish on them but there’s something satisfying about fooling fish with Dobson flies.