The Mosquito, Pale Morning Dun, Blue Winged Olive, Adams, and Light Cahill each have a useful role in a trout fly box. Choose among them by looking at the insects on the water, matching their size and profile, and watching where trout are feeding. No five patterns cover every hatch, but understanding these classics gives you a practical starting point.
Over the years, I've found that knowing when to use a pattern matters more than simply carrying it. Here is how to put these five dry flies to work, and when to consider something different.
1. Mosquito Dry Fly: A Small, Subdued Searching Pattern
The Mosquito dry fly offers a gray, understated profile for situations where trout are taking small insects at the surface. Treat it as a general-purpose option rather than assuming its name identifies exactly what the fish are eating.
Consider it on mountain lakes, quiet stream margins, and slower water where you can follow the fly and observe the trout's response. Early or late in the day can provide opportunities, but visible feeding activity is a better reason to tie it on than the clock alone.
On still water, watch for cruising fish and place the fly ahead of their path. On moving water, begin with a controlled, drag-free drift. If trout are clearly selecting a different insect size or silhouette, switch to a closer match rather than relying on the Mosquito as an all-purpose answer.
2. Pale Morning Dun: For Light-Colored Mayfly Duns
The Pale Morning Dun dry fly is a useful choice when trout are taking light yellow or cream-colored mayfly duns from the surface. For anglers fishing the Rocky Mountain West, it is a pattern worth considering when a local PMD hatch is underway.
Match the natural insects' size and overall profile before worrying about a perfect color match. Despite the name, do not assume every PMD opportunity occurs in the morning. Hatch timing varies with the water and conditions, so let the insects and feeding fish guide you.
Choose this surface dun imitation when fish are actually taking floating adults. If trout are bulging beneath the film or refusing the dun while continuing to feed, consider an emerger or cripple that better matches the feeding stage.
3. Blue Winged Olive: For Small Olive Mayflies
The Blue Winged Olive dry fly imitates small olive-colored mayfly duns, including those commonly called Baetis. It fills a different role from the pale-bodied PMD when the insects on the water are smaller and darker.
Look for olive mayflies in the drift and trout feeding steadily on them. Carry more than one size so you can respond to the actual hatch rather than make one hook size serve every situation.
If a trout inspects but refuses a well-presented BWO, try one size smaller before making a larger pattern change. First check for drag, though: a smaller fly will not solve a leader pulling the imitation across the current. If the fish are taking insects below the surface, change the feeding stage you imitate rather than only the size.
4. Adams: A General Mayfly Searching Pattern
The Adams dry fly is a practical searching pattern when trout are looking up but you cannot identify a specific hatch. Its mixed gray and brown appearance suggests a range of mayflies without depending on a precise color match.
Use it to cover likely feeding lanes when there is no obvious reason to choose a more specific imitation. Select a size that fits the insects you see or the profile you want to present, and give it a natural drift.
The Adams is a starting point, not a substitute for observation. When trout are selectively feeding on a clearly identifiable hatch, a closer match in size, silhouette, or riding height may be more useful.
5. Light Cahill: For Pale Mayflies, Especially on Eastern Waters
The Light Cahill dry fly imitates pale mayflies such as Ephemerella invaria, associated with Eastern streams and rivers. Consider it during the late-spring and early-summer hatch where that insect is present, while checking local timing rather than relying on a fixed calendar.
Its pale body and upright wings also make it an option when the insects in front of you have a similar size and outline.
The PMD and Light Cahill overlap as pale mayfly imitations, but they should not be treated as identical hatch labels. Choose between the actual flies by comparing their size, body color, and silhouette with the naturals. You do not need to carry both in every size simply because both are classics.
Start with a drag-free drift. If trout continue taking naturals while refusing the fly, reassess the match and feeding stage before adding movement to a drifting mayfly imitation.
Choose the Fly That Fits the Water in Front of You
Use the Mosquito or Adams as searching options when the food source is uncertain. Consider the PMD, BWO, or Light Cahill when the insects and feeding activity point toward a more specific mayfly match. Local hatch information can help you prepare, but observations on the water should guide the final choice.
If a trout looks at your fly but will not take it, work through presentation before repeatedly changing patterns. Our guide to Dry Fly Refusals: 5 Fixes covers drift, casting angle, tippet, fly profile, and feeding level.
About the Author
Nick Nickens has 60 years of fly-fishing experience across the Rocky Mountain West, through every season on the river. He spent four years working as a fishing guide in the region and has tied thousands of flies commercially.
2 comments
Jilly
My Dad always loved his Light Cahill flies – it was the only fly in his vest!
Jake Lowden
I love these older classic ties!