Baetis Emergers (Blue Winged Olives)

With Blue Winged Olive hatches starting to make their mark on most open streams, I thought it would be a good idea to cover the next phase in the life cycle - Emergers (click here for a review of the Baetis Nymph).

Emergence is the point in the mayfly lifecycle where the nymph undergoes its penultimate molt into the first adult (dun) stage. As with most mayflies, BWO’s emerge mid-stream – the nymphs rise to the surface in a half swimming, half floating manner. Once at the surface, the nymph hangs there in a near horizontal position while the cuticle splits longitudinally at the thorax and the adult literally crawls out of its skin onto the water’s surface. This process usually takes several seconds and is sometimes complicated by the adult getting stuck part way out (stillborn). Emergence is the most vulnerable stage in the mayfly lifecycle.

In the hour or so leading up to emergence, the nymphs become more active as they jockey themselves into position in preparation for the event. Some will even make a few trial forays off the bottom before they make their final ascent to the surface. At this time a Baetis nymph worked in the middle to lower levels of the water column can be devastating. As the hatch proper gets rolling, trout will often focus on the nymphs as they near the surface. Again, a Baetis nymph suspended a few inches under the surface will produce good results.

Once the hatch is in full swing it will usually be the emerger that gets the most attention.

If you imagine what this stage might look like to a trout you would likely come up with some kind of nymph/adult fusion fly – and that is exactly what most emerger patterns look like. There are several BWO emerger patterns listed in the fly tying literature, and a few available at your local fly shop. But the pattern I like to use most often is a simple modification of my Baetis nymph pattern:

Baetis Emerger (deer hair wing)

Hook: Mustad 94840 (or equivalent), #16-18

                                    Thread: 8/0 medium olive

                                    Tail: olive Antron

                                    Abdomen: medium olive dubbing

                                    Rib: white thread

                                    Thorax: medium olive rabbit dubbing (a few hairs picked out as legs)

                                    Wing: natural gray deer hair or CDC

Baetis Emerger (CDC wing)

The Antron tail imitates the translucent portion of the empty nymphal shuck as the adult works its way free. The deer hair or CDC wing represent the adult that is just starting to emerge above the surface. When fished properly this fly should sit with the nymph portion of the fly just under the surface, being held afloat by the deer hair or CDC. To accomplish this I apply dry fly dressing to the deer hair only (the CDC pattern is fished without dressing). I also make sure the Antron and dubbed body are wet before fishing the fly (I will often apply saliva to ensure surface penetration on the first few casts). Note that the fly will still hook fish even if it does land askew. I use the CDC version on flat water and the deer hair version on rough riffles and runs; although the deer hair version will usually work on flat water as well.

The olive/gray color combination will match 70% of the BWO hatches you may encounter but there will be times when the naturals do not live up to the blue winged olive designation. This past weekend I fished a slow trickling hatch of tiny dusky gray Baetis mayflies. My traditional olive/gray Baetis emerger pattern was refused several times before I switched to a more exact gray/gray emerger pattern – after this, the takes came consistently on the first or second cast to rising browns.

Weather tends to play a key role in BWO hatches. Some of the best Baetis hatches are on days where the weather is less than ideal. Days of unstable weather with a mix of sun and light rain squalls are ideal – most of the action will be from mid-morning to late afternoon. Never let foul weather deter you from following through with your fishing plans.