It’s graduation season! All across the country high school seniors are preparing for that long awaited moment when they can walk across the stage, grab their diploma, and head out into the world. For four long years they have worked and grown on their way to becoming adults, and now it’s their time to shine.

In trout streams throughout Yellowstone Country a similar right of passage is taking place. Though, there are no caps or gowns, and the graduating seniors are being eaten alive by trophy trout.

Like students progressing through high school, Salmonflies – Pteronarcys californica (Tare-uh-nar’-sis cal-uh-for’-nuh-kuh) – spend four tedious years as nymphs in our rivers, and at the end of the fourth year they hatch out into the world to reproduce and start the cycle anew creating the next freshman class. Freshmen, naturally, are smaller when they start school, and slowly grow as they become sophomores and juniors until they finally reach maturity as seniors.

Salmonfly nymphs are a profound food source for trout in all of our iconic waters like the Madison, Yellowstone, Gallatin, and Henry’s Fork. Simple imitations like the Rubberlegs arguably catch more fish throughout the season than any other fly. But, this progression of size is important for fly fishers to recognize, and understanding when to throw a freshman and when to throw a senior can make or break your day.

During the spring and early summer our rivers are flush with graduating seniors, and fish are on the hunt for hefty, size 4-6 imitations. While the season progresses, though, the only nymphs remaining in the river are the juniors (size 6-8), sophomores (size 8-10), and freshmen (size 10-12). As anxious as large trout are to take a size 4 or 6 rubberlegs before and during the salmonfly hatch, they can be equally reluctant to eat the big nymph afterwards, because all of the big bugs have graduated. This is where the underclassmen prove their worth. Smaller stonefly imitations like size 8-10, or even 12, rubberlegs can be extremely effective seasonlong nymphs all through Yellowstone Country.

It’s also important to remember that, in addition to Salmonflies, our rivers have a multitude of other stoneflies. Golden Stones, Yellow Sallies, Nocturnals, and many others all have their own progression of sizes and unique colorations. So, be sure to remember these underclassmen after graduation season has passed, and have a robust selection of smaller stonefly nymph imitations ready for this upcoming season in Yellowstone Country.