West Mayflies: Spring Blue-winged Olives

Being a fly angler in a state like Idaho—which still observes the traditional opening day—can test the patience of your soul.

In the weeks and days preceding the opener, the rivers, spring creeks, and many tailwaters throughout the Rocky Mountain states see the first beautiful days of spring, along with an abundance of Baetis (Blue-winged Olive) mayflies that come with them.

Idaho anglers wait patiently for the last Saturday in May before casting a line over these hatches and spinner falls, despite watching fish greedily chugging on every insect that comes through their chosen feeding lanes throughout most of May.

Blue-winged Olive is the fitting generic term for this mayfly, and it’s frequently shortened on fly shop dry-erase boards to “BWO.” Shop regulars know that the BWO acronym rarely leaves the board from spring through early summer.

Adult BWOs have smoky gray wings and olive bodies, and they range in size from #16 to #22. The larger #16-20 duns generally emerge in the spring and the smaller micro duns in the fall. Spinners have longer tails, darker bodies, and translucent wings.

Spring BWO activity can be prolific, beginning in March or April on many Western streams, and peaking through the month of May.

Unstable spring weather also brings days of warm air and thunderheads. Insect activity often ebbs and flows while shadows from the clouds move overhead in 10- and 20-minute intervals. When it’s cloudy, the insects hatch and the trout feed. When sun hits the water, the activity slows considerably. On solid overcast or even snowy and rainy afternoons, the action never stops.

As with other mayfly hatches, BWO fishing can be divided into imitating emergers, adult duns, and spinner falls. On warm, overcast days in April, May, and June—again, depending on where you live or are fishing—it is common to have all three transitions happening at once.

Before the hatch, swing small soft-hackle patterns to imitate actively swimming nymphs.

Fishing the emergence can be as simple as dropping a small Pheasant-tail Nymph just a few inches below a small yarn or dry-fly indicator. To catch fussy film feeders, try a Quigley Cripple tied on an open loop and dressed so that the post is above the water, and the abdomen and tail are below the surface. The important part is the loop knot, which ensures that the fly pivots properly, and does not sit horizontally on the water. A tight knot can make the fly sit flush when it should be vertical to give the proper illusion of an emerging mayfly.

Wiggling Wonders

Fishing duns and dying spinners can be challenging, as BWOs frequently move and wiggle their bodies while they drift in the surface film.

This rear abdomen wiggle is barely perceptible, unless you hold your face close to the water like a trout. Years of guiding from float tubes on Idaho’s Silver Creek afforded me ample time to closely observe this action.

On many occasions, while fishing over blanket BWO hatches on Silver Creek, the slicks and glides of the freestone Big Wood River, and some other Western rivers, I convinced myself that the fish were keying on the movement, and I decided to imitate it.

I knew from streamer fishing that open loops allow flies to swing freely and look more natural.

I knew that extended-body flies provide clear profiles of the insect’s rear and, finally, I knew that dressing flies with desiccant powder helps them ride higher, allowing fly bodies to move with the subtleties of the current. Combining these bits of knowledge changed my fishing, and instantly increased my success.

I drew strike after strike by positioning myself above a target and feeding the fly on a short drift to the fish’s snout. I watched as the current and breeze moved the fly and swung it back and forth against the loop knot, allowing the extended body of the fly to telegraph to the fish. All was right with the world.

I use the Duncan loop knot, although there are many loop knots, including the nonslip loop knot, that also work.

I prefer desiccant powder products with brush-on applicators over “shake” bottle varieties. With a brush applicator, you can put the powder exactly where you want it. This is important when fishing cripple patterns, where you may want the post to float, but the abdomen and tail to sink.

For the wiggle technique, coat the entire body with desiccant powder. It doesn’t matter which brand you use, just be liberal with it. This may mean looking for the least expensive variety.

The Baetis Hatchmatcher or any other extended-body BWO pattern works with this technique. The only requirement is that the hackles are tied thorax style so that the fly rides high, allowing the fly to pivot. Use nylon monofilament instead of fluorocarbon tippet material so that the tippet doesn’t sink too rapidly and ruin the effect.

Fishing in the spring is pure bliss, with plenty of eager fish and strong hatches. Give the dead-drift wiggle a shot when you come across educated fish and the Baetis are thick on the water.

John Huber is the author of Fairsized Creek: 12 Ways to Catch More Trout on the Fly (Pruett Publishing, 2002). He lives in Picabo, Idaho. E-mail him at johnrhuber@yahoo.com.