BWO emergence

[dryflyguy]

I recently had a discussion with an old FF acquaintance about blue winged olives. And I mentioned that I would really like to see an overcast/rainy day. As the BWO's always seemed to hatch better in that kind of weather.
And this guy told me that the general belief that they hatch better in that kind of weather is a myth that's not true. And that they hatch just as well on bright sunny days too.
They just don't stay on the surface of the water for any length of time on sunny days - kinda just pop right off I guess. And you don't really see many of them
Conversely, during rainy or cold weather, they struggle to become airborne. And that's why you see a lot more of them on the water then.
Now this guy has been FF a lot longer than me. And I really respect his opinion.
But I had to disagree with him on this.
I've been fishing only dry flies for well over 30 years now. And when the fish aren't rising, I'm constantly looking over all sections of the stream. And if BWO's were hatching - and not riding the surface at all - I still think I would have seen them.

Now, I'm not saying that they DON'T hatch on sunny days. I have also seen them then - and had some fishing to them.
But the rainy days by far have been when I've seen the best hatching IMO.

Just wondering what the rest of yinz think about this

 

[OldLefty]

I have to both agree and disagree with the person you spoke with about BWO (Baetis) emergences.

Many years ago I went fishing with a friend to fish (hopefully) a Baetis hatch. It was a bright, sunny day in March and my friend commented that he may not expect much hatch activity because these flies hatch best on cloudy, overcast days.

I informed him that, while the hatch may go on for a longer period of time in overcast weather, I would expect a good hatch on this sunny day, as well.

That day we had bugs galore and great fishing - on nymphs before and after the hatch and on dries during the hatch. Granted, we only had about an hour and a half of good hatch activity. It was more concentrated in a shorter time period, but there were lots of bugs.

I agree that, if flies are hatching you will see them. They may not remain on the surface for long; however, you will see them both on the water and as they make their way from the water to the streamside flora.

Most any hatch will seem to be "better" when the weather is cold/cool and overcast. The duns ride the surface longer for a couple of reasons. I do believe, though, that hatches can be just as prolific in clear weather, as well.

 

[Fishidiot]

Can't say I've tracked this in any remotely consistent or scientific way - however it has been my general experience that BWOs do tend to appear more on rainy/cloudy days.

With that said, I've had some great BWO fishing on Letort on bright, sunny, winter days

 

[dryflyguy]

I should also add here that air temperature seems to play a role in things.
On days when I have had good fishing to them on sunny days, it was quite cold - probably in '30's, or low '40s at best. My friend who I discussed this with told me that's because those low temps also keep the flies on the water longer - just as rain does. And that's a very good point for sure.

One other thing too. Our discussion never got to this because my friend - who runs a fly shop - got pretty busy then.
Anyway, I've always wondered about BWO spinners - ( talking about Baetis here)
I have been fishing them in march for many years now. Sometimes for 4-5 days in a row. And have never noticed any kind of spinner fall. I usually stay on the water until dark.
Am I missing something here?

 

[gutcutter]

dryflyguy wrote:
One other thing too. Our discussion never got to this because my friend - who runs a fly shop - got pretty busy then.
Anyway, I've always wondered about BWO spinners - ( talking about Baetis here)
I have been fishing them in march for many years now. Sometimes for 4-5 days in a row. And have never noticed any kind of spinner fall. I usually stay on the water until dark.
Am I missing something here?

Yes. Yes you are.
If you're talking about the Baetis variety of "BWO".
I wondered that for years, and found that when I saw spinners in the air, why the still rising trout never took them. And like you, I never saw them on the water. I caught a few fish on them, but only when I lost sight of the fly and thought they were taken as nymphs or emergers (I often see duns and spinners at the same time.)
Frustrated on one occasion, I seined a stretch below where the fish were rising and was very surprised to catch a ton of spinners. In the water, not on the water.
My research led me to realize that Baetis crawl or dive into the stream (usually in an upstream riffle which is tough to see the small bugs land) and lay their eggs on the substrate instead of dropping them onto the surface and having them sink to the bottom.
Once I started using a sunken spinner, the mystery was solved.
Here is a pattern I use with krystal flash wings and a wire abdomen:

A few guys in my flyfishing circle have made it a point to try and catch at least one trout on a BWO every month of the year. I have done it on a BWO dry fly during a few of my years when I fished a ton.
A few of us have done it. One of my buddies is trying to do it with the same dry fly this year. It is a deadly pattern and I bet he will.
Finally, yes, they do hatch on beautiful days. All year long. Sometimes the hatch is more amazing than those rainy "BWO days", but I agree that the fishing (not necessarily the hatching) can be better in the worst weather.
Sorry for the lengthy response.

 

[dryflyguy]

Gut -
That's interesting.
However, I never even see spinners in the air. And I do lots of looking.
Was starting to wonder if maybe they fell after dark

 

[afishinado]

Great thread.

After fishing for a very long time, I have no handle on or any confidence in predicting when, where or if a BWO (baetis) hatch will occur on any stream.

The spinner post by Gut is very interesting and eye opening...thanks.

 

[Maurice]

It could be that on Sunny days in general fish do not rise as well...which may explain why the BWO fishing on Sunny days isn't as good.

 

[pcray1231]

I've always been told the same as your friend said, that sun or no sun they hatch. But high humidity days (which in spring, generally means cloudy/drizzly), they struggle to dry their wings and thus float for an extended time. Usually leading to seeing more flies ON the water and more rising fish.

It does seem to hold true.

They seem to hatch from slower water NEAR fast water, for instance, side water and eddies. That would add to the effect of seeing more on the water if they don't get airborne, cause they go around and around in those eddies and collect in greater numbers. Also, quite often these areas are a bit shallower, and since it's a daytime hatch, fish are reluctant to go into these areas if the sun is full bore. So that enhances the better fishing aspect of wanting it to be cloudy/drizzly as well.

As for spinners, yeah, their timing is erratic and inconsistent, so trying to time it is tough. The females often actually land on DRY LAND and crawl underwater, and lay the eggs on the substrate. Kind of a reverse ISO. I've no clue what happens to males. Once or twice I've seen mid stream rocks sticking up that have quite a few Baetis spinners on them. I've never targeted areas below with wet flies, but perhaps I should....

Another curious thing about the Baetis hatch is that it comes in "waves". Many times you'll be on the stream, and a hatch starts up at noon or 1, everyone catches fish, and then it dies off. 3/4 of the anglers think it's over and leave. Then at 3 or so another wave hits. Then another around dinnertime. It also seems that early in the season the first wave is the biggest, and as it wears on later in the season, the later waves gain in size.

For those in freestone country, these BWO's are of the Baetis variety, not Drunella varieties. Different beast.

 

[dryflyguy]

FWIW -

I was on yellow creek (bedford co) yesterday afternoon. Bright sunny day - although quite chilly. Don't think that the air temp got out of the '30's. The stream was at a nice level and clear. Water temp - 45 degree
And the fishing was very slow. There were a few spurts of BWO's, that got a couple of fish to rise very sporadically. But just not enough bugs to get any good rising activity.
The few that did hatch , rode the surface for quite a long time - due to the cold temps.
I just don't think that many were hatching. And I spent a lot of time looking between the handful of fish that I caught

 

[krayfish2]

From my experience, the early season hatch seems less impacted by blue bird skies. As the hatches continue into spring / early summer, cloudy days do seem better for numbersof bugs on the water. Is that becbecause they are easier to see in those conditions or does it actually take them longer to get airborne?

I'm starting to be a believer in low pressure being a bigger influence than cloud cover. If you think about it, steady showers and drizzle usually accompany a low pressure system. I can see how less atmospheric pressure exerted on the surface of the water may lend itself to heavier hatches. Keep an eye on it this year and see what you find.

 

[SteveG]

The spinner talk is interesting. I was out the other day on a limrstoner, fishing a small riffle that had fish taking what I believed were emergers. I only saw midges in the air, so I cycled through various midge emergers and dries, and got some close looks, but no takers.

Then a mayfly appeared and began dropping to the surface repeatedly, and I assumed it was laying eggs. I tied on a bwo dry, and the first cast got me onto a fish lol.

Is it possible they have more than one egg laying method?

 

[pcray1231]

It's more likely they were taking dries and you weren't seeing them....

Kray, I've played with the pressure idea. The problem is, that bugs "decide" when to hatch when on the bottom of the stream.

The water pressure even at shallow depths is many times that of atmospheric pressure. So picture the atmospheric pressure difference between a hurricane and a bluebird sunny day. To a bug, it's akin to being a quarter inch deeper or shallower.

The only place it could play a role at all is whether, and how quickly, they succeed in breaking the surface tension. So if you're saying that cloudy or sunny, the bugs TRY to hatch, but on high pressure days they get to the surface, don't break through, and die by the millions as emergers, but on low pressure days they make it to the surface, well, I suppose that's a possibility, but I have trouble buying it.

Same goes for fish being turned on or off by a rapid pressure change. I think it's much more likely they turn on and off by a change in light/temperature/flow, which often accompanies a rapid pressure change.

 

[JackM]

It's all about the timing. They will hatch when they will, and I doubt atmospheric conditions, whether barometric pressure or relative sunshine makes a damn bit of difference. The "better hatch" perception is probably about emergence variables, maybe a little of miniscus strength, but more likely the time it takes to alight once in the film. And, as Maurice mentioned, the willingness of trout to rise to the surface rather than focusing on swimmers heading to the surface.

 

[JackM]

I was on Spruce once in March. It rained lightly for a while between 9-11 AM. Then, the sun poked out, BWOs started being visible and the water started boiling. For about 30 minutes, I had non-stop surface action, then it slowed. The sun stayed bright, but I caught fish at a much slower rate after the initial flurry of hatch activity.

 

[krayfish2]

Pat,
What I'm suggesting is.... you arrive at the time of year when the nymphs become active and the hatch started. You get 'x' amount of bugs hatching on a partly sunny day with rising or high pressure. The following day (or preceding day), you have a falling or low pressure and 2 times the number of insects hatch. You think that it was day's in life cycle, minutes of light, temp, etc. that triggers the emergence? You fell 100% confident that atmospheric pressure has zero - little to do with it? I have nothing to support my position other that hours and hours on the water chasing hatches. I'd have to say there is some relationship between heavier hatches or prolonged periods of hatching. It doesn't seem to impact all species though and I haven't noticed much influence to caddis hatches.

noticed some influence on Hendrickson, March Brown, Iso, Cornuta and Hebe.

 

[pcray1231]

You think that it was day's in life cycle, minutes of light, temp, etc. that triggers the emergence?

Well, that kind of thing likely determines whether the entire hatch period is early or late or on time. i.e. if Sulphers AVERAGE starting on May 10 in this stream, those factors may make it happen 2 weeks early or 1 week late.

For daily ups and downs, I think it has far more to do with daily weather. Not sure if light or temperature has a bigger effect. I wouldn't be shocked to learn that the total number of bugs that hatch during a full day is rather consistent. But that, say, a rapid rise in temperature makes it happen quite suddenly, appear heavier, and end earlier, while a more constant temperature makes it happen at a slower pace all day long. Maybe slow enough that we don't really take notice, nor do the fish!

And I won't say atmospheric pressure has 0% to do with it, no. Think of it this way. For a hatch to happen, first, the bugs have to somehow "decide" when to hatch. I don't think pressure can play a part here. But having "decided" to hatch, now they have to succeed. Pressure could play a part in determining the % who succeed.

The logic is this. The "decision" happens when nymphs are on the bottom of the stream. A stream has varying depths and water pressure is many thousands of times greater than air pressure, so huge variations in atmospheric pressure are equivalent to tiny variations in depth. Further, the pressure in a stream is chaotic due to current. Pressure variation is just very high from place to place. Atmospheric pressure differences would have such a minor effect as to easily get lost in that noise. It just can't be a "trigger". Temperature or light could be.

But, once the decision is made, mayflies are a bug that's strategy is to do things en masse, so that even if the success rate is very low, throw enough chances out there and SOME will succeed. If those few that succeed lay thousands upon thousands of eggs, the species survives. At the surface layer of the water, the atmospheric pressure would have a fairly large effect on the "density" of the meniscus, high pressure making it denser, and thus more difficult to penetrate. I find it possible that pressure makes it more difficult for bugs to break through, leading to a higher % of failed hatches and fewer bugs which make it to the surface. Nonetheless, IF this were true (and I don't know it to be, I'm just allowing the concept), the bugs are still down there TRYING to hatch, and what pressure would do is lower their success rate.

 

[dryflyguy]

I would also doubt that atmospheric pressure has anything to do with it.
I've had good fishing to them when warm and cold fronts have moved in.

Getting back to the sunny/rainy day thing:
During the discussion with my friend that triggered this thread, he told me that the nymphs would have no idea whether it's sunny, overcast, or rainy outside the water - maybe a valid point .
However, when your out fishing later in the season - say in May - the sulphers wait until the last hour of the day - and sometimes after dark - to start hatching good. They seem to somehow know when there's less light above, right?

 

[Maurice]

I believe that with evening hatches the species could wait for "dark" or low light period of the day to hatch. Just like the spinners wait til evening or the dusky time of day. Nymphs could crawl around and wait til it gets darker...

Once I chased the GD hatch at Yellow and for three hours or so I had good fishing to nymphs and emergers and was excited as I anticipated the spinnerfall in a few hours. It was about 3:30pm and a thunder storm rolled through. The sky got dark, I mean black! and guess what...all the spinners came out of the trees and began their dance...I was turned around. This lasted about 30 minutes til the storm passed and the sun came back out....the spinners went back to the trees, the duns started hatching again and that night there was NO spinnerfall of note. Couple here and there. They were all discombobulated.

 

[pcray1231]

dryfly,

There comes a depth where light doesn't penetrate. But it's well deeper than your typical troutstream. In the ocean, it's around 500 ft, give or take. In a stream with cloudier water, I'm sure it's less, but we're not talking