Tuesday, July 9, 2013


The title of this entry is "The Mayfly."  In order to be absolutely correct about it - I should say that the fly in the spotlight is called the March Brown by fishermen.  The high flalutin, fancy name for it is Stenonema vicarium.  Chinese name.  But, I'll get to the fly shortly.

The Holston River was extremely high and muddy today due to incessant rainfall we experienced here in Tennessee and all points upstream that have watersheds to the Holston River and tributaries.  

There was not one angler on the water.  I figured as much, but my job is to survey the water and not the parking lot or the weather.  Boots on the ground is what its called.

You've all seen pictures of the black crowned night heron on this blog.  Well, here is a sort of unusual set of pictures.  This is a "very" immature black crowned night heron.  They are difficult to find and I lucked out this morning.  These youngsters are very sensitive to human activity and usually remain hidden in the deepest recesses of foliage.  I think the lack of boats on the water lately due to the storms has allowed the immatures to remain in the open hunting areas near the shoreline. 

I have a really nice collection of black crown shots in all stages of life.  Now, all I need is to discover their nesting sites and photograph them.  Therein lies the challenge.  
Oh - the mayflies.  Forgot.

So, there I am plugging along down the side of the river when I felt little puffs of fluff against my neck and cheek.  I then saw insects lifting off the water by the hundreds in the immediate vicinity of the boat.  I haven't mentioned it often, but I have been fly fishing the limestone and freestone streams of Pennsylvania and Maryland for over thirty years.  Yellowstone Park and Clarks Fork of the Yellowstone River are not strangers to my fly rod.  Neither is the Elk River in Colorado or the Snake River in Wyoming.  I've been tying fishing (trout) flies all that time also.  I'm not an entomologist by any stretch of the imagination, but I do know a tiny bit about stream flies.  The flies I was seeing today were called March Browns, or Stenonema vicarium.  
Mayflies are elegant and delicate and present a mystery to those who have not taken the time to study them.  The mayfly originates from an egg laid upon the surface of the water by the female.  She will flit up and down touching her abdomen to the surface depositing her eggs.  I'll ramp up the time line here.  The eggs hatch into a nymph.  The nymph resembles a hard shelled larva that spends it's life using it's six legs to crawl under rocks on the bottom of streams, and, I guess lakes by the looks of it.  This part of the life cycle can last up to a year to a year and a half.  There are other species of flies that can spend up to four years in the nymph cycle of life.  Those would be termed Caddisflies.  But, lets stick with the fly of the hour for now.
I happened onto the emerging cycle of life for this mayfly.  The nymph actually leaves the bottom of the stream, lake, river and ascends to just below the surface of the water.  The nymph skin then starts to split open, usually down the back and the emerging "dun", the finished product, claws it's way through the surface tension to finally come to rest on the surface.  We'll back up here a second.  Often times the insect can not break through the surface tension and will drown.  It requires oxygen when the nymph skin (shuck) splits.  It has only seconds to claw, crawl, struggle through the tension to the outside air.  The nymphal shuck or nymph skin often times will not release from the insect and will hold it under water preventing surface tension break through and causing the bug to drown.  This stage of life is known as the emergent stage.  

The shot above shows the March Brown "Dun" on the surface still attached to the nymphal shuck.  He will struggle about until the shuck breaks away and he is free of it.

Trout in streams key in on the various stages of emergence.  They will focus on the nymph as it crawls onto the top of underwater rocks and lifts off for the surface.  They will sweep through the nymphs as they rise in the water column toward the surface and trout will attack the emerging mayflies as they try to break through the surface tension.  Experienced fly tiers will create fly patterns to emulate each of these  mayfly stages as a trout can not be tempted to any other fly pattern once he becomes obsessed with one particular emergence stage.

The photos above indicate a "dun" on the surface with the nymphal shuck still attached and also a shuck that has been shed by some other dun.

The two pictures above show the free March Brown dun sitting on the surface waiting for his wings to pump up with body fluid and swell his wings solid so that he will have power to lift off the surface.

These pictures depict the dun, which is the finished product, waiting for the wings to fill with fluid and gain strength for the next stage of his life which is to procreate.  

They flutter about and cause surface disturbance which usually attracts fish below.  On a trout stream the surface would be boiling now with a trout feeding frenzy.  Here on the river things appear to work differently.  I think that because the trout streams are more narrow - the struggling flies are more obvious/apparent to the fish.  Then again, I've seen some very wide trout streams, especially in Wyoming.  There are no trout in this river.  These fish are warm water species, bluegill, crappie, bass, redear sunfish and the like and maybe they aren't excited by a mayfly hatch like trout are.  I'll have to research that.
There is one other mayfly often mistaken for a March Brown by novice anglers and that is the Gray Fox.  The two flies are very similar except the Gray Fox is slightly lighter in color.  Both flies emerge in late May and June and both share identical wing patterns.  By the way - the hook size of these flies would require a #12 light wire hook. Both species sport two tails also.  Some mayflies have three tails.  I am curious why there are no fish smashing into this free buffet.  Oh, these flies will find a nearby tree or bush and cling to the underside of the foliage.  Then at a mystical time, usually at dusk, they will swarm over the water and fly straight up into the sky where they will mate.  After a couple hours the males will fall dead to the surface of the water and lie there with wings spread out like tiny crosses.  This is the final stage of life.  They are known as spinners.  Again, trout will gorge themselves on these dead flies.  And yes - there is a fly pattern that anglers use to mimic the death stage.  The females will swoop down close to the surface and touch the tip of their abdomens against the surface dropping their eggs.  Then, they too will die and become spinners.  The cycle is then set to start over again and the species is perpetuated.  How bout that?
 They were everywhere.
Good to see my old friends.

There ya are.  Another day on the river.  I hope you enjoyed the diversity.  See you later and thanks for your readership.  Its appreciated.