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Tuesday, November 2, 2010

Baetis Complex - Part I - Blue Wing Olive Mayflies

Here in Northern California and as we head into the fall and winter it is time to get ready for the main portion of our blue wing olive season. This is an over view of the Baetis Complex, or in common terms the Blue Wing Olive complex, that we will encounter here in Northern California and in the west.

Family Baetidae

The Baetis group of mayflies represents the most complex family of mayflies. The Baetis are of the Swimmers group of mayflies. There are sixteen genera and more than 60 species of Baetidae that occur in the west. This is often referred to as the Baetis complex. It is considered by many, to be the most important of all western hatches. The BWO hatches are so diverse and can be so prolific that they cause more selective feeding, more often than any other insect group. This is why getting to know and understand the Baetis complex is so important.

The most important thing to remember is that fly patterns for one species of Baetis will be just as effective for the others. You will need to change the size and the color as you encounter the different species on the river that you find yourself.

Emergence and Distribution

The Baetis complex is a large and widely distributed group, found in great numbers in all of the western states. With proper adjustments in size and color of your imitations you'll be able to match any Baetis hatch. For the fisherman, knowing the identification to the Baetis complex level, is as much as you practically need to know. You will need to focus your attention on finding an appropriate imitation and then fishing it with the most productive presentation. It is more important to get to the business of fishing and not worry about which species it may be within the complex. In simpler terms, collect a sample, match size and color and get on to fishing.

The Baetis complex hatches can occur at anytime of the year, depending on the species, the geographic area and the current weather conditions. Most adults emerge in the winter and spring. The exact timing of the hatches depend upon the species and the water temperatures in the waters that they live. Because the Baetis complex is so large, you must study the hatches on your own home waters in order to predict the hatches with any accuracy. Here in Northern California, the BWO hatch is primarily a later fall, winter and early spring hatch. With that said, because of their abundance and diversity, it makes the Baetis complex, or Blue Wing Olive mayflies, important at one time or another, on almost every western river and stream.

The daily emergence times of the various species change with the season but are typically in the warmer part of the day. In early spring the hatch will be from early to late afternoon, when the air and the water are the warmest. Mid summer hatches might move towards morning, or more commonly evening, when the conditions are cooler. In the fall, the hatches move back towards the warmest hours, again occurring between late morning and early afternoon.

It is well documented that the Baetis complex hatches occur on cool, overcast and even wet and snowy days. On warm and sunny days, the hatch is often truncated into a brief period. On cloudy days you'll get a trickling hatch that can go on for two to four hours with trout up in the water column and feeding all that time. On a bright day the hatch will often be heavy, but last only a half an hour to an hour. On these days the hatch can be over before you realize it is going on.

Because of the small size of the Baetis complex, the hatches of these mayflies are often overlooked by fisherman. The fish rarely make this mistake. For some reason when you have hatches of Blue Wing Olives happening at the same time as that of a larger insect, the trout often ignore the larger meal and become selective to the Baetis complex. A lot of anglers make the mistake of fishing imitations of the larger bug and the fish are focusing on the smaller Baetis.

Some fishermen consider Blue Wing Olive duns to be the most important stage of this complex, but studies have shown that the nymphs are a consistent and important food item nearly every week of the year. Trout feed heavily on nymphs during the pre-hatch activity and can also become selective to spinners when they fall in abundance. Because of their small size, emerging adults are often trapped in the surface film during the transition from nymphs to duns. This is often the “feeding zone” that trout concentrate on. Ralph Cutter refers to this as the "killing zone". This is where having cripple imitations will be very effective. Feeding trout will often ignore nearby floating duns. You need to be aware of this multiple, masked hatch, and when this happens and have fly patterns to match emergers, duns, spinners in order to fish a Baetis complex hatch effectively.


The one saving grace of the Baetis complex is the way you can reduce their complexity by considering them all one group. They can be matched with color and size variations of the same set of flies. One problem is the broad spectrum of water types in which they live. You need to carry patterns that float on riffles, others that combine flotation with a fairly accurate silhouette to fish on nervous, uneasy water and finally you'll need flies that show the exact form of the insect on water so smooth that flotation is never a problem.

The Baetis complex hatch, or the tangle of hatches, is where the use of the "one precise right fly" just doesn't work. If you read John Gierach's book, Trout Bum, he has referred to fishing the BWO hatch as the "progression" of a blue wing olive hatch.

As the day goes along, you might begin by fishing a Baetis nymph pattern down deep along the bottom because you know there are lots of them down in their habitat. Then you'll switch to the same nymph fished shallow. You'll begin to notice duns and some trout will start feeding on them and you can be successful changing to a dry fly. But sometimes the trout will get finicky and you'll notice they're taking cripples, so you'll have to change to an emerger. And so forth, right through to the late afternoon spinner fall.

So what John Gierach has stated is that if you stick with one pattern through a blue winged olive hatch, you'll deal with some trout but probably end up frustrated. If instead, you observe the different stages of the hatch and how things change as the hatch progresses, and change patterns as the fish do, you'll continue to catch trout throughout the hatch. That's the goal.


So, pick up a new flybox, or recycle an old one, and label it BWOs. Fill it with patterns that match the size and color of the BWOs on your stream or river. Fill it with, nymphs, emergers, duns and spinners. Make sure you have dun patterns for (1) riffles (2) nervous water and (3) smooth water. If you do this you'll be ready for a Baetis complex hatch where ever you roam.

I will follow up this article with 4 additional articles with specific information on the habitat, flies, and techniques for presenting flies for the Baetis nymphs, emergers, duns and spinners

You can pick up Dave Hughes book, "Western Mayfly Hatches" at Amazon books by going to the following link. It is where most of this information came from.*&s=books&qid=1287687533&sr=1-1

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Have any Questions or Comments? Let me know, Clay.