Help Understanding Mayfly Behavior

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Shawn_H

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Sep 13, 2022
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Delmont, PA
So I was on Penn’s Creek today from about 9:00 - 3:00. From about 11:00 on until I had to head home I was seeing large dark(ish) colored mayflies with a very bright orange/yellow egg sac on the rear - very noticeable. My guess was they are Hendricksons. I was not seeing any sailboats on the water. So my assumption is these have either hatched the prior day or somewhere else on the river. Are they technically spinners? Didn’t look like what I would typically associate with spinner activity. Maybe they haven’t been fertilized yet and are still waiting to become spinners. Sorry if these are dumb questions. I like to understand what I am seeing.

There were somewhat sporadic risers. Often splashy. I couldn’t really identify anything specific so I tried various things. I had a few last second refusals on a light Hendrickson pattern but did not hook any. All the fish I hooked on top were on emergers - grannom pupa and Barr emerger - trailing behind various dry flies I tried.
 
Yo Shawn - by "large", do you mean size !4 or 12? If so, Hendricksons is my guess. Early for March Browns, which are huge (#10 or even bigger) on Penns. Either way, if there are egg masses, they would be spinners (as opposed to duns). For the early stage of spinner fall, if there are splashes rather than leisurely sips, I use a Dun Variant with rusty body in the right size. Pheasant Tail isn't as durable as dubbing, but I use both rather than a stripped Coachman Red hackle. For the egg mass, a ball of dubbing at the rear, using the right color is good. In the dim light, I use fluorescent dubbing - really helps the visibility. Usually the Rusty Spinner with spent wings - poly, Antron or the newer EP Trigger Point - is my go-to.
 
I tie a Hendrickson pattern specifically for this situation...

It has a dark grey poly wing tied more or less in the center of the shank, a reddish brown or tan body, wide splayed tail and FULL palmered hackle just slightly longer than the hook gape. I also tie a variant with a small blob of yellow/orange fur to simulate an egg sack, but most often they don't seem to care.

The most effective way to fish it is with a twitch or by skating it a few inches across the surface on a fully greased leader, which is the reason I palmer hackle the fly.

Another way I have used it with extraordinary results is to stand upstream of the targeted fish, ideally in a riffle. Then I'll cast downstream, hold the rod high keeping my line and leader off the water so the fly just bounces on the surface of the broken water.

I'll move the fly upstream, bouncing and skating then cast back down and repeat. I also target the slack water on the sides of the riffle with skates or twitches.

Absolutely deadly (for me) when the spinners are dropping off eggs clusters...
 
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Yes I'd estimate about a 12 in size - bigger than a sulphur but not gigantic. It's crazy how each of these mayfly groups seems to have very different behaviors. The only one I really have a handle on at this point is sulphurs - they seem pretty predictable.

This event I was seeing then I guess is the spinners depositing eggs - or maybe getting ready to - I didn't really see them bouncing on the water. It certainly wasn't a "spinner fall" - there were not dead spinners on the water.

I've spent a pretty good amount of time on the water the last several years - I can honestly say I've almost never seen large amounts of "sailboats" on the water. Does this ever happen? 🤔
 
Shawn_H said:
I've spent a pretty good amount of time on the water the last several years - I can honestly say I've almost never seen large amounts of "sailboats" on the water. Does this ever happen? 🤔
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Definitely. Some of us chase these emergences with relish. You have to put in the time and judge the best place and be there.
 
DGC said:
Definitely. Some of us chase these emergences with relish. You have to put in the time and judge the best place and be there.
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I've been trying. My best experiences so far have been Grannom emergence (not this year 😢) and some really solid sulphur spinner falls.

Had what I have to assume was a good sulphur emergence as well - but it was basically dark so I couldn't really see the bugs - don't think it was a spinner fall though based on what I could see.

Olives have been challenging for me - I've seen a bug here or there and had some success but never what I'd consider a strong hatch. And the bigger bugs - Hendrickson, March Brown, Drakes - I've yet to experience those floating on the water.
 
Those were the female egg layers, so yes spinners. They will hover over the water in late evening and fall down to the water surface to drop their eggs. I have egg layer patterns for this with a small ball of yellow on the end for when that starts. I love fishing the egg layers for the Hendrickson's and sulphur's (orange eggs). After they are over you can switch to a spent spinner pattern, like a rusty spinner, and even use that the next day if fishing early mornings.
 
Don’t forget the majority of hendricksons drop their eggs from up high into a riffle, most times most don’t dip to the water to deposit their eggs like caddis will for instance. Then die and hit the water. Usually takes place on warm less windy nights but in case of Hendrickson I’ve seen good falls in late morning also.
 
Drifly said:
Don’t forget the majority of hendricksons drop their eggs from up high into a riffle, most times most don’t dip to the water to deposit their eggs like caddis will for instance. Then die and hit the water. Usually takes place on warm less windy nights but in case of Hendrickson I’ve seen good falls in late morning also.
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Good info - so bottom line is they were likely just flying around and more or less unavailable to the fish. I did notice that they seemed to generally be flying downstream - which is the opposite of what I would expect. My guess is the risers that I did see and target basically had nothing to do with these Hendrickson spinners flying around.
 
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