Shortwing Stonefly Hatch
They are known by many names: Nocturnal Stonefly, Midnight Stonefly or by their official name Shortwing Stonefly (Claassenia sabulosa), but whatever you want to call them they have become an important mid-summer hatch in Southwest Montana. These close relatives of Golden Stoneflies have become more numerous over the years as the longer warmer summers have increase the hatch’s duration. Mainly found on freestone rivers and streams, these stoneflies provide a welcome bridge between the prolific hatches of spring and the summer terrestrial season.
The hatch usually starts mid to late July and can last well in August. The sight of empty husks on rocks near the water will indicate that the hatch is on. The hatch is usually overlooked by anglers who see the husks but don’t see adults flying, and therefore forego the opportunity to through dry flies. The key to taking advantage of this hatch lies in its name. The emergence of the nymphs happens predominantly at night (Nocturnal or Midnight Stone) and the male adults have “short wings” and do not fly. The female adult does have fully developed wings and does fly, but only to return to the water to lay eggs. The egg laying usually happens late-afternoon or close to dark. Because the hatch occurs well into summer the adults are not usually found on streamside foliage, but rather under rocks along the bank or gravel bars in the middle of rivers. As the nickname suggests these guys really don’t like the light. When flipping rocks near discard husks they will scurry to find shade when exposed and boy can they move. Especially the short winged males. When they fall or are blown into the water (or thrown by the curious angler) both the males and females will run across the surface at an impressive rate. This makes fishing dry fly adult imitations fun, because the twitch from mending, or an intentional twitch by the angler, can induce a spectacular eat.
The best way to “match the hatch” is to start fishing size 8 or 10 variegated brown or tan stonefly nymph patterns around mid July. Either straight nymph rigs, or as a dropper under a big dry, it doesn’t matter you’re just trying to imitate the nymphs migrating to the banks pre-emergence. Once husks start showing up along the water’s edge try searching with tan, cream or light brown dry stonefly patterns. Low Rider Stones and Water Walkers fish well with their low profiles. Chubby Chernobyl’s in tan also work well. Trout will take dries all day when the naturals are around, but the best time to capitalize on the dry fly bite is early morning (we’re talking first light) and mid-afternoon all the way to dark. Many hopper patterns will work well too, which is nice because hoppers will start playing a bigger role as the Shortwing hatch dies off in August.
The Shortwing Stonefly hatch is an excellent way to raise trout to big flies as the dog days of August set in. One last hoorah before the terrestrials take over the dry fly scene. These stoneflies can be found all over the West (the Yakima experiences an excellent Shortwing hatch), but the freestones of Southwest Montana hold and abundance of them which offer great fishing opportunities during the mid-summer. Stop by our Bozeman Fly Shop or check our fishing reports heading into July and we will keep you informed when things get going.