It’s about time for the big bugs, yes, the bugs with a scientific name that makes people think more of dinosaurs than aquatic insects.
Yes, it’s salmonfly time on the Big Hole River, or if it isn’t, it will be in the next few days. Because of press deadlines, I have to write this column a week ahead of time, so if my crystal ball occasionally seems a bit fuzzy, that’s the reason why. Still, if salmonflies aren’t yet active on the Big Hole, they are on some other streams—somewhere in western Montana.
The salmonfly, or giant stonefly, or Pteronarcys californica, is the aquatic insect that gets anglers excited across much of the Rocky Mountain west. Our rivers have a lot of aquatic insects and stoneflies are one of the Big 3 of aquatic insects, the others being mayflies and caddisflies.
Stoneflies, of the order Plecoptera, come in a great variety of sizes, colors, and individual species. There are over 3,500 known stonefly species in the world and there are still more being identified. They’ve been around for a long time. One website (flycraftangling.com) suggested that if we could somehow time-travel back 250 million years and take a close look at a prehistoric stream we’d find stoneflies, and looking pretty much the same as they do today. In fact, stoneflies are related to another prehistoric survivor, the cockroach.
Like most aquatic insects, stoneflies spend most of their life as nymphs, crawling around on and in the bottom of rivers and streams, though there are also some lake-dwelling species. Some species are carnivores and prey on other aquatic organisms. The salmonfly, however, is a “detritivore,” meaning it eats vegetative stream debris on the bottom of the stream.
While fish feed on stonefly nymphs all year around, stoneflies come to our attention when they become a flying, winged adult insect. We call them as something as ordinary as golden stone, or whimsical, such as yellow sally or skwala, or the big bugs, salmonflies.
That final phase of life is an amazing process. The nymphs begin to migrate to the shorelines of their native river, then crawl out of the water, usually at night, often climbing up shoreline vegetation such as grasses or willows, where they crawl out of their exoskeleton and emerge as a flying, winged insect. An angler walking along the edge of a river might first notice salmonflies clinging to a willow branch, where they stay mostly motionless as their wings dry.
Still, as living creatures always do, the salmonflies sort things out and find a consenting adult of the opposite sex. We humans won’t notice, but stonefly males produce a drumming sound using their abdomens, attracting females, and nature takes its course.
The females return to the water to deposit their eggs, fluttering above or on the water and releasing eggs.
Fish take note of that fluttering stonefly and it’s an easy bite of protein.
Meanwhile, the eggs settle to the bottom of the stream and eventually stonefly nymphs hatch, starting the process all over again, as another generation of giant stoneflies grows and matures for the next three years until, finally, they also crawl out to become a flying insect, ready to perpetuate the species.
We anglers look to that last, glorious phase of the stonefly’s life, casting various imitations of an adult salmonfly onto the surface of rivers in hopes of attracting the interest of large trout in search of an easy meal.
I’ve been one of those optimistic, though often frustrated, anglers over the last 30 years. I can’t say that I’ve ever had a day on the river when big fish threw all caution to the winds and repeatedly attacked my humble imitations, though it happens often enough that I find it addictive, even when the trout end up refusing to take the bug. That explosive, attacking rise is the stuff of heart attacks.
And on that note of optimism, I think I’d better retreat to my fly-tying table and create a couple new fake stoneflies.