Flyfishing Entomology


Re: Vermont Siphlonurus


From: Matt
Received: Tuesday, April 05, 2005 10:49 AM

I am a guide here in Vermont on the White River. Its a large free stone river with some deep pools and lots of fast water. It is a trib of the Conneticuit river. I use a drift boat to better my clients chances. Straight to the question. Would there be a species of Siphlonurus in this river coming off in May. I never seem to witness the hatch, but these lime colored spinners are red on top and sort of lime on the underside. They have two distinct long black tails as an adult, and they are in the air with the remaining hendricson spinners. Our Hendricson spinners have red, or maroon undersides, and are a little larger than this unidentified bug. Can you help me with this mystery?

Thank you,


I can't solve the mystery for you, but I am happy to share my thoughts on your observations.  I will start by paraphrasing your observations:
- You have observed mystery mayflies (m/m) in spinner stage on Vermont's White, which is a freestone river with both deep pools and fast water, and a tributary of the Connecticut River.
- The m/m spinners you have observed are a somewhat smaller than Hendricksons (Ephemerella subvaria), have two distinct black tails, are red on top and lime underneath, and are in the air with the Hendrickson spinners, which have red or maroon undersides.
- You have not observed m/m hatching.
- You suspect that m/m may be Siphlonurus, and are wondering if that is likely.
As I'm sure you already realize, male and female spinners of Ephemerella subvaria are different in size and body coloration, but both have three tails, so your 2-tailed m/m spinners must be of another genus.  
Okay, here is what I can tell you in answer to your question about Siphlonurus:
-  Although I am unable to find any official reports of Siphlonurus in Vermont, three species of Siphlonurus have been reported just across the border (from south eastern Vermont) in New York, so I would conclude that the could certainly be in Vermont as well.
-  Eastern Siphlonurus species tend to reside in limestone waters like those in eastern Pennsylvania.
If the m/m spinners are forming mating swarms mid to late afternoon, when (I assume) you are encountering the Hendricksons similarly engaged, it is likely that they are hatching during daylight hours.  So, one possible explanation (for your not having observed the emergence) is that they are not water-emergers.  If that is the case, they might be Maccaffertium (Light Cahill), Nixe (Ginger Quill), Siphlonurus (Gray Drake), Stenacron (Cahill), or Stenonema (Gray Fox).  However, the fly in the ointment is that none of these 2-tailed spinners are described as having black tails.  As a matter of fact, a cursory examination of my references hasn't yielded any medium-sized spinners with 2 black tails.
So, I guess I'm just as stumped as you are.  The only thing I can suggest is that you capture a spinner and photograph and measure it (in millimeters exclusive of tails).  If you are able to get a decent macro-photograph, and will send it to me as an email attachment, perhaps I can be of more help.  Alternately, you might look at one under low level magnification, and provide a description of the fore wings (plain or marked), and the hind wings (absent, minute, small, medium, or large in relation to the fore wing size), and the legs coloration, and anything else you are able to observe.
Sorry I have not been able to be of more help.


Created: 08/13/2005   Last modified: 08/25/2006    www.FlyfishingEntomology.com