Fishing the hex hatch for big trout is pretty well known, especially in the upper Great Lakes states, but what about the other hex hatch? Did you know that warm-water species gobble up these giant mayflies too? Read on to find out where, when, and how to get in on this exciting and little-known fly fishing opportunity.

Trout and the Hex Hatch

Much is written about how big brown and rainbow trout go nuts over the mayfly Hexagenia limbata and its close allies. These late, night-hatching, giant mayflies are legendary in Michigan and Wisconsin, and certainly a topic of discussion for trout anglers in much of the upper midwest to Pennsylvania and New York. Nothing is more anticipated on the Au Sable and Pere Marquette (in northern Michigan) than this annual hatch. Anglers from around the country converge there to try their luck catching truly “fish-of-a-lifetime”-sized trout on dry flies.

What Is a Hex?

Hexagenia limbata, the giant burrowing mayfly, better known to fishermen as the hex, is one of North America's most widely distributed mayflies. They reach their greatest densities in the Great Lakes states but are found in Canada all the way to Mexico. They can be found in every U.S. state except for Arizona and New Mexico. They occur in lakes, rivers, and streams but are limited to slower reaches of moving water that have sand and muck bottoms. This vast distribution means opportunities for fly anglers across North America.

The Hex is also one of the largest mayflies, with the winged adult measuring nearly 3 inches from the head to the tip of the tail. But even more remarkable than its size is its synchronous and massive hatches. Where I live in east central Minnesota, some time

around the first week of July, the aquatic nymphs leave their burrows at the bottom of a lake or river and swim through the water column to the water’s surface. Here they molt into the sub-adult winged form, typically called a “dun” in fly fishing language.

They rather quickly fly to nearby trees, bridges, or even buildings and lampposts to rest and then molt once again into the adult form, known as a “spinner.” The adults form massive mating swarms that at times are so large and dense that they are detected on doppler radar and appear as thunderstorms. This is a fairly common occurrence above the Mississippi River from Lacrosse, Wisconsin to Minnesota’s Twin Cities. Within 24 hours of molting into the adult life stage, they mate; the females lay eggs back into the water, and they die, spinning back to the water’s surface.

Fishing During the Hex Hatch

Fish eat hexes when they are aquatic nymphs and when they are living or dead adults. This massive food source, wherever it occurs, is a major driver of fish behavior because fish key in on this food source so strongly. This in turn affects fishing, because fish will ignore most other offerings. In other words, it is hard to get fish to eat something other than a hex nymph or adult when they are so abundant.

I was first introduced to fishing with hexes in an interesting way. My Grandpa Max would take me fishing as a young boy for panfish on a southern Michigan Lake. We would stop on our way to the lake to buy bait at a typical baitshop. Here, at the right time of year, he would buy live “wigglers” for bait. As I learned many years later, these wigglers were actually Hexagenia nymphs. There was (and still is today) a cottage industry in Michigan that consists of collecting Hex nymphs by using handheld dredges or sifters to suck them up in the muck, and selling them commercially as bait. We would bait our long cane poles, complete with bobber and sinker, with the big nymphs dipped from a minnow bucket, and catch our share of nice panfish.

But back to fly fishing! While hex nymph patterns certainly are used while nymph fishing, nymphing during the emergence is not an effective technique. There are simply too many nymphs swimming to the surface, and your nymph is lost in a sea of the real deal. The excitement of the hex hatch is fishing dry flies, either duns or spinners.

Where and When

As I mentioned earlier, hexes are found across most of the North American Continent. They reach their peak abundance in the upper Great Lakes States. From reading online or in fishing texts, one would think the only place where hexes provide a reliable and exciting fishery is in northern Michigan, and to a lesser extent, Wisconsin. Not for warm-water fishing! Massive hex hatches occur all along the Mississippi River, and in Lake Erie, Lake St. Clair, Mille Lacs, Lake Champlain, and perhaps to a lesser extent, on countless other smaller lakes and rivers in prime smallmouth bass country. I have heard, but cannot verify, that some very large hex hatches occur in the marsh country of Louisiana and east Texas. Wherever you find muck, sand, and good water quality, there will be at least some hexes and fish that eat them.

Where I fish along the Mississippi, just south of Minneapolis and St. Paul, I can expect to start seeing hatches around the first of July. If it's been a warm spring and summer, then I’ll see them a bit earlier. The fourth of July is often prime time. In Downtown St. Paul, starting in mid-June I always paid attention when I walked under street lights. If the hexes were hatching, I would see the dead spinners on the sidewalks, which meant it was time to go fishing!

North of this latitude, the hatch will be later, and to the south, earlier. Because of their abundance, if you are paying attention, it's not too difficult to dial in the time. Warm, humid nights with little to no wind often will spark a hatch. I pay the most attention to the wind. If is it going to be calm, get out there!

The Gear and Techniques

I typically fish from a boat when I am warm-water hex fishing, mainly because I most often am either fishing the Mississippi River, or a big lake like Lake Pepin, which actually is a natural widening of the Mississippi River. While there are places to wade fish in this big water, it's just easier and more comfortable in a boat. That’s not to say you can’t wade, though. Most trout anglers fishing the hex hatch wade.

Rods

When I am in the boat, I like to have three rods ready to go. I fish a 4-weight which I like for the smaller fish I anticipate catching like bluegills and mooneyes. I also like to have a 6-weight along for pretty much everything else I think I am going to catch on a hex fly. On the third rod, which could be as heavy as a 7-weight, I like to have some type of 2 to 2.5-long minnow-type fly tied on. Often when fishing the hex hatch I will see showering baitfish escaping from larger predators. Having the minnow fly on a rod will give you shots at these fish, which could be bass, big crappies, or even pike.

Lines and Leaders

Floating weight-forward lines matched to the rod are fine. I like tapered knotless leaders as they won’t pick up all the empty shucks that litter the water. You do not need to get too fine with your tippets. In fact, because you are going to be fishing in low-light conditions, you don’t want to be breaking off a fly and having to retie. 3X or 4X is fine enough.

Flies

I like a hex dun that is buoyant, durable, and whose wing is not too large. I find large wings will twist your tippet badly. Both foam flies and hollow-haired flies (deer, moose, caribou) fit the bill. The color of the naturals does vary, but generally speaking, you want a fly that is dark brown with some yellow. A yellow wing aids in visibility when it starts to get dark.

While I don’t often fish the spinner fall, it is a good idea to have some spent spinners in your fly box. I prefer synthetic materials like antron for the splayed-out wings on my spinner patterns.

I recommend having these in sizes 6, 8, and 10. Even though these large flies are easy to thread through the hook eye, it's a good idea to have some ready on a wire threader. You will be glad you did when it starts to get dark.

Most fly shops carry a variety of hex patterns. If they don't I recommend the largest mayfly dry they have available. Size is more important than color. Things like stimulators or even yellow Chernobyl ants will work.

Other Gear

A good headlamp is indispensable for this type of fishing. I like the ones that are rechargeable. A net can be handy, as can a Boga-grip or similar device, in case you are lucky enough to catch a bowfin, gar, or big catfish. And of course, a good forcep for quickly and safely removing hooks is always essential gear.

Tactics

Unlike traditional hex fishing for big brown trout, the warm-water version does not have to happen in total darkness in the middle of the night. I rarely fish that late, in fact, I like to get on the water in the early evening with plenty of daylight. I then search for calm shorelines with overhanging trees. If the hatch is on, you will see the sub-adult duns hanging by the thousands from the trees. You will also easily see the windrowed empty shucks on the water.

When you find hexes in the overhanging trees, even with the sun still above the horizon, start carefully looking for rising fish. At first, there will only be a fish here or a fish there, but my experience has shown me these are the easiest fish to catch. Cast your fly to these risers, let the fly sit for a few seconds, then move it ever so gently. That usually does it. Keep moving along the shoreline and repeat.

I believe these fish are eating the resting sub-adult hexes that have fallen out of the trees and onto the water’s surface. I don’t think the fish are taking the dun as it is emerging from the nymph, because when I accidentally hang my fly on an overhanging branch covered with the resting duns, and I go in and retrieve my fly, I knock a bunch of bugs into the water. When I then go back out a cast length away, fish respond to the dozens of duns now on the water.

Where I fish on the Mississippi, I see this phenomenon on a grander scale almost every night I fish when the hex hatch is on. A train track runs right along the river (or Lake Pepin) edge. When a train passes, the vibration or wind from the train knocks the duns from the trees, and some drop into the water. Instant action!

As the sun begins to set, the true hatch slowly begins. Millions of the larval nymphs leave their mud burrows and begin swimming to the surface when they molt into the dun. Dimpling fish begin to appear away from under the trees and well out into the lake. At this stage of the hatch, fish respond well to a fly. Again, just a little movement helps.

Soon as darkness approaches, on the best nights from the fish’s perspective, too many bugs are hatching. Fish are rising everywhere, but it becomes difficult to compete with the naturals. I have seen Lake Pepin, which is two miles across, come to a slow boil with rising fish for as far as the eye can see. For me anyway, it becomes impossible to catch a single fish at this stage of the hatch. I head back to the landing with just barely enough light to see.

As I am motoring back to the landing, sometimes there is a mating swarm of hexes above my head that stretches for miles. Gulls, terns, and purple martins are zipping through the sky feasting on this incredible resource. Later, the giant mayflies will die and spin back into the water. There, the feast will continue in total darkness.

Final Thoughts

Fishing the warm-water hex hatch truly is a special time. The action can be fast and furious, and at times it can be really frustrating. How can you not catch a fish when hundreds are rising within casting distance? For me, part of the charm is not knowing what you might catch next. I’ve caught 20in smallmouths on my 4-weight, 12-15lb channel cats, big freshwater drum, super nice crappie, bluegills, white bass, and others all in a single night. I have yet to catch a gar or bowfin on a hex, but I’m still trying!

And what is also amazing is that no one is doing it, at least not where I fish. I can honestly say that I have never seen another fly fisherman fishing the warm-water hex hatch when I have been out.

Do you like to catch fish on dry flies? Do you like to catch nice fish, and a variety of fish? Enjoy not fighting crowds? Find a hex hatch and give “the other hex hatch” a try! Have any questions, reach out to a Fly Fishing Expert here on Curated for answers and for the right gear!