Understanding Mayflies
The most imitated species of aquatic insect is the mayfly by leaps and bounds. You may
have seen the word “Ephemeroptera”. It means “short-lived winged insect”- (ephemero-
meaning short lived) and (ptera-meaning winged). There are hundreds of species of
When mayflies are hatching and trout are rising, it is a fly fishers dream that came true.
Day in and day out, however, this is not the case. To begin with, in the U. S. and Canada,
with few exceptions, mayflies only hatch between the months of March and November and
this long period of time occurs only in the southernmost areas of the U.S. where trout
waters exist. On most streams, the majority of the hatches occur during the months of
May, June and July. When hatches do occur, many of them only last for a short period of
time, a few days or less in many cases. During the hatch mayfly duns may emerge for
only an hour or two and not return to the water as a spinner until dark or even well into
the night in some cases. So all things considered, on any given stream or lake, trout are
only feeding on hatching mayfly duns or spinners (what you will be imitating with dry flies
in other words) a very small percentage of time. When they do, you want to be ready for
Most of the mayflies that trout eat are taken in the form of nymphs. Most of the species of
mayfly nymphs are available throughout the year although they may not always be easily
acquired. This, of course, points out the fact that an imitation of the mayfly nymph, day in
and day out, should have a higher probability of success than the dry flies we all love to
Another very important point is that even when there is a hatch of mayflies in progress,
your odds of catching trout on an imitation of the emerging mayfly nymph fished beneath
the surface of the water, or in the surface film, are usually better than they are fishing a
dry fly on the surface.  The emerging mayfly nymphs are the helpless ones and the trout
know it.     
Once the emerging process is over, the mayfly is going to be airborne just as soon as
possible, more often than not, within a few seconds, although some struggling cripples
may not make it. When mayflies return to the water as spent spinners, however, the
situation may swing in favor of the dry fly for the first time. It is during this time that you
may actually catch more trout on a dry fly than a wet imitation fished below the surface.
This all depends on the particular species of mayfly you are imitating however.   
Since this may sound somewhat a bit complicated, lets get started proving that it is not,
rather a simple matter of knowing something about mayflies and how you go about
fooling the trout into thinking your fly is a real ephemeropterd.
For years anglers have been successful in matching a particular mayfly that is hatching
simply by catching a sample of the fly, nymph, dun or spinner, and selecting a fly from
their box that closely resembled it. The key to it all, however, is for one to understand the
behavior of the particular mayfly you are trying to match. To do that, you first need to be
able to identify the mayfly at least to the point that you know which family of mayflies it
belongs to. Some hatches are so common that they can easily be identified down to the
species. The Eastern Green Drake hatch, for example. Most of the time it is not
necessary for you to be able to identify a mayfly down to the species. In fact, in many
cases doing so would be next to impossible on a stream. You would need a microscope,
a male spinner of the species and to be able to identify its sex organs from certain keys
established for the different species.    
Scientists are able to do that in a lab. In many cases they make decisions as to what
genus a certain mayfly belongs to and then years later, discover they were wrong and
reclassify the species. They may discover that it wasn’t a separate species at all. It was
the same species as another mayfly.  The trout could care less. Even if you could, you
could not purchase of tie a fly that accurately depicted the difference in the two flies.
You can fully expect that soon after this program has been released, changes will be
made in the classification of mayflies. So don’t be the slightest bit intimidated if you can’t
identify a mayfly down to the species. Trout fishing should be relaxing and fun and this
program is certainly not meant to change that in any way. Lets get back to the key to it all.
Different groups of mayflies behave similarly –they live in similar types of water, hatch,
mate and die as spinners in a similar manner. Usually, you are in good shape if you know
which genus the particular mayfly you are trying to match belongs too. You should
understand the behavior of that group or genus of mayflies. By that we mean the type of
water the nymphs live in; the time of year and the time of day they hatch; and how they
emerge (in the surface skim, on the bottom or out of the water) and where, when and how
they deposit their eggs and die.  Matching the size, shape and color of the fly for the
particular stage of life you are imitating is one thing. Knowing when, where and how to
present the imitation is another, even more important thing. If you select the perfect
imitation and don’t present it at the right time and place using a method that presents the
fly in a manner similarly to which the trout normally observe you will usually get a refusal
just as quick or quicker than if you selected a poor imitation. Most of the time, when the
time, place or method of presentation is wrong and there is no action, the angler
unknowingly changes flies. It may very well be that the fly was not the problem at all.
Copyright 2013 James Marsh
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