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The Blue-Winged Olive Mayfly
The Blue-winged Olive mayfly is probably the best known mayfly there is. It is difficult to find a cold water trout
stream that doesn't have the little mayflies. That's not the only reason it is so well known, the name is used by
fly anglers for dozens, if not hundreds, of different species of mayflies. This is the one of several reasons
professional entomologist don't use common names of insects. Common names don't usually identify specific
species of insect. They use the scientific Latin names, and fly guys don't speak Latin very well.
Before I get into trying to explain what species should rightly be called Blue-winged Olives, let me explain why
knowing all you can about this little mayfly is so important. The mayflies are rarely absent from most trout
streams. They hatch all winter in some southernmost trout streams. Even in the middle part of the country
hatches begin as early as February and continue through April or May. Those called Eastern Blue-winged
Olives hatch mostly during the summer in some areas. Most all of them start hatching again in September and
last until the first really cold weather sets in.
The blue-winged olives are a very diverse group of mayflies. The nymphs live in about every type of running
water, but you will find the great majority of them in slow to moderate water. The nymphs often drift a short
distance in the current and relocate in a new areas of the stream. This usually occurs during the evening
During winter or early spring, hatches usually start at the warmest time of the day which is usually around 1:00
to 3:00 PM. The best hatches almost always occur on overcast or drizzly days. Perfect Fly emerger patterns
are especially useful during the hatch. Some anglers only use the duns but there are times, especially when
the water is in the forties, that the emergers work far better than the duns. Spinner falls are also important, so
you should always carry a few Perfect Fly BWO spinners along as well.
Now, I will try to try to explain what should rightly be called a Blue-winged Olive. Many of the common names of
aquatic insects include more than one species, but rarely do they include more than one genera, or particular
group from the same family of mayflies. This isn't true of the Blue-wined Olive. It encompasses species from
many different genera and worse, the name even includes more than one family of mayflies. Although most of
the mayflies called BWOs, come from the Baetidae family, it would be difficult to prove anyone wrong if they
called a Western Green Drake, a Blue-winged Olive. In fact, a few species of insects from the same family as
the Western Green Drakes, or the Drunella genus of the Ephemerellidae family, are called Blue-winged olives.
Now, if you are already confused, let me add to it by mentioning that most fly fishing books on aquatic insects
break the common name Blue-winged Olive down into Tiny Blue-winged Olives, Small Blue-winged Olives, Little
Blue-winged Olives, Eastern Blue-winged Olives and Small Eastern Blue-winged Olives.
By now, you may be thinking, why all the fuss. Obviously, they are mayflies that have blue wings and olive
bodies. Well, that would certainly help identify a mayfly as a Blue-winged olive but unfortunately, that isn't true.
The wings are usually more of a light gray color than blue, but most of them do have a blue tint to them. The
bodies are usually an olive color, but can be many shades and mixtures of greens, grays, and browns. They
can have spots and blotches of other colors mixed in. It is impossible to identify what should be called a BWO
from the colors of its body and/or wings. And, by the way, Blue-winged Olives nymphs, emergers, duns and
spinners, all stages of life of the BWO mayfly, are usually different colors from each other.
So far, all I have done is tell you how confusing the common name "Blue-winged Olive" is. I have done little to
try to help anyone identify a BWO. To do that, you have to deal with some scientific names of the mayflies. It is
otherwise, impossible. Just bear with me. It isn't necessary to remember the scientific names. I'm only using
them to try to help you make some sense out of all of this. Also, keep in mind, common names can never
positively identify most any aquatic insects. They are helpful to fly anglers but only if they are aware of the
species of insects they include.
Most Blue-winged Olives are swimming nymphs. The following is just to give you an idea of the various species
that are called BWOs:
Most of them are Baetis species including the Baetis brunneicolor, tricaudatus, flavistriga,
bicaudatus, cinctutus, and intercalaris species. You also have some Diphetor species, including
the hageni and devinctus; a Labiobaetis propinquus and a Acerpenna pygimae.
Then you have what most call the Tiny Blue-winged Olives. They are Baetis punctiventris, futile,
and dubium species. There is a Accentrella turbida species also called a Tiny BWO.
There are also some crawler nymphs that are called BWOs:
The Ephemerella excrucians is called a BWO. Then you have the Eastern Blue-winged Olives
which are Drunnella species. The are the Drunnella cornula, walkeri, cornutella, longicornis
and lata species. Next is the Little Blue-winged Olive, or Attenella margarita. Next is the Small
Blue-winged Olives, or Timpanoga simplex and lita species.
The above twenty-three species of mayflies are what are generally accepted to represent the great majority of
what should be commonly called Blue-winged Olives, but there are many other species that exist in trout streams
in smaller numbers and of less importance. Then, there are those many insect called BWOs by those guys that
think they name fit and since there are no hard rules for common names, no one could rightly say they are wrong.
Blue-winged Olives Can Be Small