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May has arrived, the days have gotten warm and muggy, the moon is waning towards a new moon on the 11th. All of those things have my senses on high alert for the first Mayfly hatch at the reservoir. To most local fishermen, the hex hatch at the Rez is a puzzling mystery. I have heard bass fishermen complain about the hatches, aggravated because the fat and happy bass feeding on mayflies and numerous bluegills often reject their lures, but to fly fishermen, the big brown bugs just mean a fun day on the water.

I love the reservoir Hex hatch because it’s the only real fly fishing around here in Central Mississippi, in the traditional “match the hatch” sense that most folks think about when they think of fly fishing. I have fished a local mosquito hatch before with success, a midge hatch (Chironomids) and I’ve managed some ant hatches, but there is nothing quite like the mayfly hatch. Along with great fishing is the added value of the opportunity to observe and understand this incredible animal. The Hex hatch at the Rez is the best thing going for fly fishing in central Mississippi.

After being initially introduced to the reservoir hatch by a fellow fly fisher and friend, (NC, to whom I am forever in debt), I’ve been trying to find out everything I can about the reservoir’s mayfly, the Hexagenia Bilineata. A lot of patterns work, the simplest is the white popper and it’s hard to beat. Due to some aggravating trips where the fish have either been selective or simply hard to hook, I have wanted to come up with the ultimate Hex pattern for the Rez. Here’s the problem, as I see it: The bream have small mouths, they don’t gulp the fly like I have seen trout in numerous videos. The bream smack it hard in a lightning fast strike and in many cases when they hit, they just don’t hook up. One reason the white popper works so well in hooking up the bream is that the popper has enough weight that when the line is stripped in tiny strips, the line will be tight when the bream hits it with their lightning fast strike. The tight line will almost set the hook by itself if the fly fisher is holding it tight against the grip to keep if from slipping. The bream prefer cripples to dead spinners and the stripped popper gets that attention so any optimum pattern needs to sit in the water with enough weight to allow the fly line to come tight, just for an instant, and to look like a cripple. Tiny fast strips basically keep the line tight enough to help with the hookset. I use an articulated abdomen on my “Hex-a-flex” pattern so that the abdomen is at an angle to the fly, not just straight, to look more like a cripple.

To tie the optimum pattern I wanted to know everything I could about the reservoir insect and to do that I needed to identify it exactly, but I’m no entomologist. Thankfully I was able to identify the exact insect from a 1979 Benthic study on the reservoir I found online. I then began researching that particular insect and I found online another 1960 study with very specific information about the bilineata, Biology of a large mayfly, Hexagenia bilineata of the upper Mississippi river.

Several things I have read in the study has made me compare my own experiences. For example, the study states “On warm summer days, H. bilineata subimagoes usually begin molting about 2 p.m., 8 to 18 hours after emergence. Molting continues into the evening, with a peak being reached about 4 p.m”. I have experienced this afternoon molting peak myself. On cloudy to partly cloudy days the bugs may begin coming off the branches pretty good from about 2 to 4 and then in massive numbers toward the evening. On sunny days, the bugs tend to stay on the branches until late evening. On those same sunny days the bugs would simply fly back to the branches if disturbed (i.e. knocked off their branches by a frustrated fisherman wanting to start a bream blitz).

I have never experienced any emerging hexagenia mayflies and probably won’t because emergence occurs at night; however, I have been able to predict hatches by watching the moon tables closely, trying to find times of ultimate darkness. Obviously around the new moon there are dark nights but I have also noticed hatches that occurred on nights that had moon, even as much as 98% illumination, but usually they were on nights when the moon set before midnight, leaving a moonless and dark early morning. The following statement from the study supports my observations, “Although subimagoes were collected by river boat captains between 7 p.m. and 9 a.m. C.S.T., over half of the emergences were reported between 1 and 4 a.m.”

Last year as I began checking for mayflies I encountered a lot of smaller, brown mayflies in the grass. There would be a few in the trees but most were in the grass. At first I was excited, thinking that maybe they were early volunteers and maybe a hatch was coming, but unfortunately there were none on the following day. After some research I put two and two together and realized that they were males left over from a previous hatch. The males are smaller and after mating with one female they will continue to mate until all the females are spent. They have no digestive system and no mouth so they don’t live long but they can live long enough to be around the following day before they die of starvation or the birds finish them off. I then found out how to tell a male from a female by looking for the clasper appendages the male uses to cling to the female and the next time I found bugs in the grass, they were in fact all males. To anyone experiencing this, you are too late, and the fish do not hang around for very long after the spinner fall. Another indication that you are too late is if you encounter a heavy decomposition smell.

The only other predictive information I have is simply a common refrain among trout fishermen that to predict a Hex hatch, “Look for a night as dark as the inside of your hat”. Combing through hatch dates that I have preserved I have looked for similarities. I thought the dark night thing was going to provide me the key, a much needed index to the hatches:

May 19 2018 Moon did not rise until 10:07 am. dark between 1 and 4
May 19, 2020 Moon did not rise until 4:28 a.m. dark between 1 and 4

Then I looked at the following hatch dates, which were big hatches:
May 28, 2018 Moon set at 5:30 a.m. 98% illumination (i.e. the moon was up and bright between 1 and 4 am!)
May 31, 2019 Moon rose at 4:15 am dark between 1 and 4, full moon and the sky was clear!

After continuing I found that dark nights in some cases mean something, but just the dates are almost as predictive. By far the best predictor I have is checking the grills and windshields of co-workers that travel around the reservoir in the morning. There is no better indicator than finding a fresh collection of mayflies in a co-workers grill. Also, the lights of Madison, Ridgeland area gas stations are fairly reliable for attracting some reservoir mayflies. The appearance of just one on a light is significant because they don’t hatch one at a time. If there’s one bug on a light, there’s a million somewhere else.

So a fly fisherman wanting to key in on an event that provides blitz type fishing for about 12 hours means keeping up with the hatch dates, watching for dark night-times, primarily in the 1 am to 4 am time period and paying attention to windshields and lights around the Rez. One caveat, do not depend on fellow fishermen. Once a fishermen is hip deep in a Hex hatch, he can’t be depended on to drop everything and go start calling everyone. And who can blame him.

But at least now I totally understand the old mayfly joke: Two mayflies sitting at a bar, girl mayfly turns to the boy mayfly, “Let me guess, you flew in last night, you only have 18 hours to live and you just want to have sex one time before you die.”

Postscript:

Well the bug showed up but it wasn’t on a windshield, his timing was off and he got slammed on the bumper instead. The end result was the same, from this bug on a bumper I knew the mayflies were hatching. The only problem was that the wind was blowing hard from the south and it was raining and promising to pour down.

And I found them, seemingly unbothered by the rain (below).

This big female dun was a true dun color but by the end of the day she would have turned brown. I am guessing the color is an indication of a new arrival, having emerged in the wee hours of the morning rather than before midnight.

The photo below shows both a female dun and some male imagoes which is an indication of a hatch the day before as well.

Even though the waves were pounding and a steady rain was falling, the bream were waiting on the bugs and were very willing. I put a nice mess in the basket and put the rest back. They seemed to particularly like my deer hair parachute (below).

And this is where they ultimately wound up…