Why should you get the blues over a group of insects that produce some of the most consistent and productive fly fishing opportunities in streams and rivers coast to coast? Well, if you try to understand this complex group of genera and species that produce multiple broods and frustrating selective feeding by trout, you might find yourself writing a blues tune or two. Blue-winged olive is just one common name often used to describe this complex array of genera and species in the family Baetidae. Others include: little iron-blue quill, little slate-winged olive, little slate-winged brown quill, tiny western olive, and little western iron-blue quill. Confusing? If the number of common names is an indicator of the importance of a particular group of insects, then these small mayflies must rank near the top of the list. The names listed above are just a few of the common names that have been used to describe different species in the family Baetidae. Because these species are quite difficult to distinguish confusion often occurs. While one angler refers to the great hatch of blue-winged olives he just fished over, another discusses the pattern he used to imitate the little iron-blue quill hatch. Quite often they are talking about the same insect.

While anglers may be confused over common names, entomologists are just as confused over the way to split or lump genera and species in this family. Nineteen different genera and a whopping 153 species are currently described in the family Baetidae in North America. The distribution and importance of many are poorly understood, largely due to the difficulty of deciphering one species from another. Another frustrating aspect for fly fishers is that some of the frequently used scientific names for major hatches of Baetis have been changed as a result of taxonomic revisions in the last five to ten years. The attached table provides a comparison of old scientific names with the new ones for major eastern and western hatches. Note that in same cases only the species name has changed, while in other cases both the genus and species names are different. To deal with this most unruly group, it is simplest to lump the major genera and species into a catchall I refer to as the “Baetis complex.” Such complexity also accounts for much of the mystifying range of colors, sizes, and hatch periods of these small mayflies known to many fly fishers as simply – Baetis.

Learning to recognize or identify even a few species of the Baetis complex is difficult. Fortunately species identification is unnecessary to fish their hatches effectively. Hatches with new scientific names still look the same to a trout, the hatches follow the same seasonal emergence patterns, and the same patterns are still effective.

Nymphs of this diverse group are all swimmers, and thus have the same streamlined torpedo body shape and swimming behavior as other families and genera of swimmers like Siphlonurus, Ameletus, and Isonychia. Nymphs in the Baetis complex can be recognized from these other genera by the following combination of characteristics:
- Small size, body length (excluding tails) 3-12mm.
- Antennae long, two or more times longer than the width of the head.
- Small, single oval gill plates on abdominal segments 1 - 7.
- Two or three tails fringed with fine hairs. If three tails present then the center tail is shorter than the
   two ourter tails.
Recognizing adults is slightly more difficult than recognizing nymphs. Adults of the Baetis complex are best recognized by:
- Hind wings either greatly reduced in size and difficult to see, or absent. When present they are long and narrow in   shape.
- Front wings with paired marginal intercalaries (small short paired veins along the outer margin of the wings      located between the long complete veins).
- Eyes of male very large and each divided into two halves.
- Small size, 3-10mm long excluding tails.

The color of both nymphs and adults varies widely. Variations from light gray to dark reddish brown, usually with olive undertones, are typical. Such color variations are not only common between two streams in the same region, but within the same stream at the same time of year. Because of these large variations in size and color, collecting specimens during a hatch is almost a must when fish become selective to these tiny morsels.

So what makes these small mayflies so important to the fly fisher? One reason is that they occur in nearly every type of flowing water habitat. Their worldwide distribution attests to their ability to adapt to many different conditions. They live in streams from sea level to over 10,000 feet high, from alkaline spring creeks to acidic mountain streams, and from hot desert streams to frigid arctic waters. For example, while studying a small desert stream in western Colorado I found Baetis tricaudatus to be one of the most abundant aquatic insects present. At the same time, during study in Alaska, I found Baetis bicaudatus a significant component of the invertebrate community. Water temperatures may be an important factor affecting the distribution of different species. Within the large range of habitats utilized by species of Baetis, the largest populations tend to occur where lush beds of aquatic plants grow in rich spring creeks, or in shallow, fast flowing gravelly riffles of freestone streams and rivers. And wherever Baetis species are abundant they provide a near constant and readily available food supply for many aquatic organisms, including trout.

The life cycles of Baetis also contribute to their importance. It is common for species to have two and sometimes three generations in a single year. The number of generations is largely determined by water temperature. Cold, high elevation or more northerly streams may produce only two generations a year, while slightly warmer streams at lower elevation or further south often produce three generations a year. Spring creeks with relatively constant water temperatures will have Baetis hatches almost every month of the year. Some of the best Baetis hatches occur from mid-winter through early spring and again in the fall. Look for winter hatches as early as January or February, and continuing through April and May. In the Rockies good Baetis hatches often begin before spring runoff muddies the rivers. The fall hatches can create some of the most selective feeding situations of the season.

The third reason Baetis species become so important is their behavior. Their activity often causes the largest fish in a stream to feed freely in or near the surface where fly fishers have their best chance at catching them. Like most swimming mayflies Baetis nymphs are very active in the water. They crawl through aquatic plants and dart over gravel bottoms. They swim in one to two inch bursts by rapidly flicking their tails and abdomen up and down. This active behavior causes many nymphs to be caught in the current and washed into the jaws of feeding fish. Studies of stream drift – the movement of insects in stream currents – consistently find Baetis nymphs one of the most abundant organisms moving in the current where fish feed.

Emergence behavior also puts nymphs directly in the path of feeding fish. Nymphs get restless just before a hatch begins, and start climbing up aquatic plants or swimming off the bottom. After a few minutes of indecision the nymphs ascend to the surface where they struggle briefly in the surface film. During a good hatch thousands of nymphs will be rising to the surface. This is a time of plenty for fish. Feeding tends to move from the stream bottom up to the surface as nymphs rise up. Even when duns are floating on the surface, most surface swirls will be from fish taking nymphs just under or in the surface film. Large fish, fish worth writing home about, can often be found gulping nymphs in small channels between aquatic plant beds. Also look for eddies or current tongues that concentrate the nymphs. Fish cruise through these areas, mouth open, like whales straining krill. Peak hatch activity varies from mid-afternoon in the cool months of winter, spring and fall to late evening or early morning in mid-summer. Baetis hatches also tend to be best on cool, wet unpleasant days. I have had some amazing fishing while casting between the snowflakes of late season winter storms.

Subimagoes, or duns, also produce great fishing when on the water. They float helplessly on the water's surface after escaping the nymphal shuck in the surface film. On cool days in the spring and fall duns may float 50 or even 100 feet before their wings dry and they can fly. Those few that finally escape the water, fly to nearby trees or shrubs where, after seven to twelve hours, they molt into the imago or spinner stage.

Mating swarms of spinners, and the ensuing fall of egg laying females, can occur anytime from early afternoon to late evening depending on the weather and time of year. Of the three life stages (nymph, dun, and spinner) spinners seem to produce the least consistent feeding activity. At times fish feed readily on the small spent-wing spinners providing exciting but demanding fishing. Other times little or no feeding activity occurs. Perhaps fish so totally stuff themselves on nymphs and duns they have no interest in the spinners. The females of a number of Baetis species crawl underwater along the sides of rocks or aquatic plants to lay their eggs on the bottom rather than on the water's surface. I have seen the edges of rocks coated with the dried carcasses of tiny Baetis spinners. A morbid sight perhaps, but one that foretells of a healthy generation to come.

Fly patterns needed for this complex group includes nymph, emerger, dun and spinner patterns. Nymph patterns are effective whenever the natural nymphs are abundant, even if no hatch activity is present. A quick kick of the stream bottom with an insect net will tell you if Baetis nymphs deserve your attention. If so, place one of your patterns next to a natural in a small dish of water. Nine times out of ten you will find that your patterns are much too big and over dressed. It is difficult for many fly fishers to believe that a size 18 or 20 nymph pattern will be seen and taken by feeding fish. Trout have amazing eyesight, however, or they wouldn’t be able to survive. When Baetis nymphs are abundant, tiny size 18 or 20 nymph patterns will consistently out-fish larger flies.

They same holds true for the remaining stages. Always check the size of your patterns carefully against the size of the naturals, whether you are fishing emergers, duns and spinners. Next select patterns that provide a natural looking silhouette on the water. Only then do you need to worry about color. Because of the frequent variations in color of the naturals, it won’t usually matter if the color of your fly is slightly different.

Of course the final, and often deciding, ingredient to your success is presentation. For nymphs this means fishing them where the fish are feeding. Sometimes this will be close to the bottom. At other times it will be mid depth or near the surface. An upstream or up and across presentation that gets your fly through the trout’s feeding areas is usually the best approach with nymphs. When fish are feeding near the surface, finding fish won’t be a big problem. However, you will usually need to present emerger, dun or spinner patterns with delicate casts and drag free floats. Upstream, downstream, or across stream presentations may all come into play depending on where fish are feeding and where you are casting from.

Over the next few months blue-winged olives will be creating some excellent fishing opportunities in streams across the entire continent. If you are prepared, only the trout will have reason to sing the blues.