The Light Cahill common name is one of the most confused common insect (fly)
names in the East. The Stenacron genus, not to be confused with its sister
genus, the similar sounding Stenonema genus, includes one important species,
the interpunctatum. This mayfly is commonly called the Light Cahill.
This mayfly is very similar to some of the Stenonema species (that were recently
changed to Maccaffertium species) which accounts for some of the confusion.
For example, the old Stenonema ithaca (now the Maccaffertium ithaca) is often
called a Light Cahill. It is also called a Gray Fox, adding even more confusion
the Gray Fox common name. Because of the confusion, you will hear anglers
mention that Light Cahills are hatching all the way from April until the middle of
September. Some of the mayflies they are referring to are not Light
Some of the other mayflies the Light Cahill is confused with are the old
Stenonema (now Maccaffertium) mediopunctatum, carolina, and modestum
species. These are usually and correctly (if there is such a thing as a correct
common name) called Cream Cahills.
The Light Cahills are also confused with the Heptagenia group of mayflies or the
Little Yellow Quills that hatch later in the season. That is why you will hear
anglers still taking about Light Cahills late in the Summer and early fall months.
There is a reason for all this confusion. The duns of these various species look
Now, I am sure all of the above scientific names are also confusing, especially to
those who are just getting started. I would make this plain and simple if it were not
for those guys who would respond with a lot of corrections in my over
simplification. Some want it simple and some want it as accurate as a snipper.
Scientific names are necessary in order to designate the insect I am referring too
or otherwise I would not use them. If I used common names only, there would be
even more confusion. For example, if I called a Maccaffertium Ithaca a
"Gray Fox" many anglers would think I was referring to a Maccaffertium varcium
or the old March Brown common name. I could give dozens of such examples.
Common names vary from region to region, book to book and angler to angler. In
order to make it simple, what I and most of the fly fishing community refer too as
a "Light Cahill" is the Stenacron interpunctatum.
These mayflies hatch from the last week of April until the end of June, depending
mainly on location, the weather and elevation of the stream. This hatch usually
only last two to three weeks at any one location but the overall duration from the
streams at the lower elevations to the higher elevation, can last up to eight
weeks. These mayflies can be found in the tiny brook trout streams as well as
the larger watersheds.
As I said above, it is easy to understand some of the confusion in the common
name "Light Cahill". There is not a great deal of difference in the appearance of
some of the Maccaffertium Stenacron and Stenonema species. They are all
clinger nymphs that look fairly similar. However, there are differences in the
behavior of some of these various species that warrant attention.
The Heptagenia group of mayflies (often confused as Light Cahills) are also
clingers but behave quite differently. When we review the "Cream Cahills" you
will find that some of those species are different colors. Some of them are almost
white. Some of them have heavily mottled wings. The sizes of these mayfly
species can vary a hook size of two and of course, the hatch times vary greatly.
For now, lets focus on the real "Light Cahill", the Stenacron interpunctatum.
Copyright 2013 James Marsh
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