YELLOWSTONE NAT-IONAL PARK — The first fish I caught was by accident.

I had drifted my two-fly setup along a likely seam close to the bank several times with no luck.

As I looked downstream for a better place to fish, my fly line dangling at the water’s edge, a 14-inch cutthroat trout darted in, grabbed my nymph like a smash-and-grab robber and darted for deeper water – an automatic hookup.

Now, that is easy fishing. And every now and then, it’s nice when the fish make it so easy, when they forgive awkward or bad casts — or in my case no cast at all. It’s a time when even a sorry fly angler like me can feel good, almost skilled.

Salmonfly hatch

The source of this fly fishing ego boost is the hatch of the big beasts of the western bug world — salmonflies.

The first sightings prompted a rush of adrenaline. There, flying awkwardly in the air along the Yellowstone River was a huge, hovering insect that can provide a lot of protein for a hungry fish.

At roughly 2 inches long, the prehistoric-looking winged insects are the trout angler’s “gimme” — a chance to cast large dry flies that fish will greedily attack. Although not a long hatch, usually lasting only two weeks or less, it may be one of the most fun to fish.

Cast away

I was deep in the Black Canyon of the Yellowstone River, just downstream from Hellroaring Creek, when the first salmonfly was sighted. Eagerly I tied on a fly known as a sofa pillow, because of its large size, that imitates a salmonfly. With about 18 inches of leader, I tied a coneheaded salmonfly nymph onto the bend of the salmonfly hook. The two-fly setup covers two scenarios — fish rising to dries have the sofa pillow to attack, while those feeding on emerging nymphs bite the conehead.

The real nymphs live under the river’s rocks for three years before drifting to the bank when ready to hatch. To slip out of their nymphal shuck and emerge into winged, mating adulthood, they crawl up onto rocks and trees like some scary alien lifeform. The shells of their former selves cling tenaciously to where they were abandoned — sometimes for years — even though the bug has long since moved on.

The salmonfly, formally known as Pteronarcys californica, is the largest member of the stonefly family, which also includes the more common yellow stonefly that hatches in abundance on Western waters. Although big and scary looking, salmonflies are also beautiful in their own way. The bug’s translucent wings are intricately patterned with honeycombed lines. Their bodies are a bright orange, as if to boldy announce: “Here I am!”

Often the clumsy adults will drop back into the river as they climb on overhanging brush and limbs. That’s why the salmonfly is often best fished near the riverbank.

Park permit

To fish inside Yellowstone National Park, anglers 16 and older need to purchase a park fishing license. The cost is $18 for a three-day permit, $25 for seven days or $40 for the season. Hooks must be barbless and no lead sinkers or lures are allowed. All cutthroat trout must be released, or as the park’s literature says, if it has a slash, put it back.

Undoubtedly there are bigger fish in the river that will gulp down a salmonfly, since it’s a large source of protein compared to smaller bugs. It’s the idea that such a trophy fish may rise to a dry fly that keeps anglers like me obsessed with the salmonfly hatch. And even if the big fish never does arrive, the often quick pace of action during a salmonfly hatch means I don’t have time to feel sorry about what a poor angler I am the other 364 days of the year.