The Mayflies of Spring

The Mayflies of Spring

Spring in the Rocky Mountains is the unofficial start of dryfly fishing season for many anglers.  After spending the winter trying to see a size #24 midge pattern on the water or being frustrated at the lack of commitment on the part of the trout to rise to Midges, spring is a whole other story.  Once the rivers/streams reach an average water temperature of around 40 degrees the BLUE Winged Olives (BWO/Baetis) start to hatch in large numbers.  It’s this first hatch of spring that brings trout to the surface to feed on the emergers, Duns (Cripples) and Spinners.  Because of the large numbers of emergers that don’t break the water surface the trout eagerly feed on them. 

Hatches usually start in the mid-mornings and continue throughout the day rain or shine.  As the weather gets warmer here on the western side, BWO’s start hatching at the end of March and continue until early May. The fall Baetis will begin to appear around late September, lasting until November. 

 Those interested should be aware that these mayflies can be found primarily during mid-morning as nymphs, slender and usually dark brown or olive colored. Adults usually join the scene near late morning and stick around till the afternoon on certain days. Lastly, spinners (when they lay eggs) can be spotted throughout both mornings and late afternoons. Although not as common with other mayflies of this region, Blue Wing Olives have a distinctive behavior all their own. 

Understanding how trout feed on the BWO hatch is key to knowing what patterns to fish.  Since the BWO life cycle is a complete metamorphosis, you can fish the Nymph, Emerger (Pupa), Cripple (Adult) and Spinner phases of the life cycle.  Since the Nymph cycle of most mayflies lasts up to 1 year you can fish any Mayfly nymph every day of the year. 

Mayfly Nymphs 

Mayfly nymphs, whether crawlers, clingers or swimmers can be imitated by many different patterns. From the traditional old school never fail: Hares Ears, Pheasant tails, Princes, Copper Johns and Barr’s Emergers to more modern patterns like the Duracell Jig, Frenchie, Quill Jig to the endless variations of Perdigons. As much as fly selection, it’s about getting these flies down on the bottom where the naturals live. Sizes can range from #14-22.  

Mayfly Emergers 

While Mayfly nymphs can be matched with a great number of different non-specific patterns, the emerging mayflies have a more specific form. There is either a trailing shuck or the more visible tails as the insects are breaking through the surface of the water. Prior to breaking loose from the bottom of the river, mayflies will create an air bubble at their gills. It’s the air bubble that will aid them in their ascent to the surface. The bugs still need to exert a tremendous amount of energy to swim to the surface. Many are never able to break the tension of the water’s surface, only to become trapped and easy pickings for trout. The rise form you will see from trout is a porpoising, where you see the back of the fish, their heads aren’t breaking the surface. Fishing a dry/dropper rig with an adult and a trailing emerger is the best option, using the dry fly to detect when a trout eats your emerger. At this point you will see fish rising in the riffles as well as in the slower tails of pools. Fishing the dry/dropper rig in the riffle won’t give trout much time to examine your flies and can hide a less than perfect presentation. In the spring the sizes are anywhere for #14-18 

Mayfly Adults/Cripples/Duns 

Like most aquatic invertebrates Mayflies are very susceptible to being eaten when they are sitting on the surface waiting for tier wings to develop and dry. They are easily spotted on the water with their sailboat profile. There are many days when the water can be covered with BWO’s and what I will do is fish an imitation that’s one size larger than the naturals. Another cool thing to do when you have such a prolific hatch is to stalk individual fish, watch it rise a couple of times and then present your flies. I almost always tie some Fluorocarbon between my dry fly and my dropper.  

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