A streamside problem that confronts most fishermen one time or another is what action to take when feeding trout refuse lures and flies. The angling experts say there’s a simple solution: Examine the contents of a trout’s stomach, determine what it is feeding on, and then fish accordingly.

Angling writers great and small have offered this apparently sagacious advice at one time or another but to me it’s fallacious. If trout refuse to take everything you throw at them, how do you catch one to examine the contents of its stomach?

I threw this conundrum at a friend recently; he told me what he tried last year when Stillwater brookies were rising steadily and ignoring his flies. He found a feeder stream where small trout were less finicky, caught a couple, and discovered they were feeding on a small, greenish nymph. While he had nothing in his fly box resembling the nymph, he was well-prepared the next time he fished the Stillwater.

I’ve never solved the riddle of uncooperative fish by with a streamside postmortem and I believe it’s a dubious exercise at best. However, at home, I routinely examine the contents of trout stomachs when cleaning them and it’s a practice I recommend. This exercise is invaluable and if nothing else, it can make you better prepared the next time you fish your favourite waters. Knowing the foods trout favour gives you an obvious advantage.

Occasionally you’ll be surprised by what trout are eating. I’ve found twigs, leaves, grass and other unidentifiable vegetable matter; one trout had swallowed a cigarette filter, another a bit of aluminum foil. What these last objects represented in the way of food is a mystery to me. But then trout strike flies that look more like space monsters than any kind of food found in their environment.

The stomach of a 14-inch trout I caught recently contained the usual mixture of insects, minnows and vegetable matter, and an object that was surprising as well as educational. While the trout was taking Mayflies, its stomach contents revealed it was an omnivorous feeder. I found caddis cases, minnows or small trout (I couldn’t tell which), nymphs, some goo that could have been Mayflies, a piece of leaf, and a large insect with a head that was easily a centimetre in width; while its body was partly digested and difficult to measure, the insect was easily four centimetres long.

This was the surprising object I mentioned above, which at first I thought was a cicada until I noticed the long, claw-like pincers. I had never seen anything like the insect in a trout before, or anything in the water like it either, and I was surprised a 14-inch fish could swallow anything so large.

The same day I caught the trout my grandson showed me his new book on fish and insects. In the centrefold was a coloured drawing of water insects and prominently displayed was the mystery creature I had found in my trout – a Water Scorpion! A quick check of the book, A Natural History of Kings County, and a chat with naturalist Merritt Gibson, confirmed that the Water Scorpion did indeed inhabit our waters. It’s one of our largest bugs, the book says, large enough to eat small fish and tadpoles.

As I mentioned, this was an educational discovery. The oversized bugs my some of my friends carry in their fly boxes will no longer be sneered at. Someday a trout may take one of them for a Water Scorpion.

I’ve been examining the contents of trout stomachs for decades, by the way, and have yet to find an earthworm. While this may be because they digest quickly, worms are not a regular food item for trout. Which brings up another mystery – why worms are such an effective bait.

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