These American mayflies spend most of their two-year life span burrowed in underwater muck banks, but near the end, they are compelled by hot June weather to swim to the river's surface, shed their nymphal shell in the surface film, and ride the current as their cellophane wings dry. They are cumbersome, nearly two inches long, and don't fly well, so they evolved to make this transition at night, when they are less visible to fish and other predators. For thousands of years, this emergence was the ultimate trade awaiting its ultimate practitioner.
It was probably in June of 1886 when Hexagenia limbata first found that the heavy dark of hot June nights was no longer safe.
For in 1884 Salmo trutta, the European brown trout, had been introduced to Michigan rivers. When God created lower Michigan's slow, sandy, cedar-swept rivers, he created them with brown trout in mind. In the fertile, cold spring water, they grow long, thick, and hook-jawed, and specialize as nocturnal hunters. They kill and eat whatever finds itself swimming in the dark: smaller trout, mice, frogs, bats.
Most of these trout have outgrown insects. The calorie cost/benefit ratio is not profitable. But they will make an exception for Hexagenia limbata.
On these nights, Hexagenia limbata run the gauntlet in the millions. Apex predator trout eat them off the oil-black surface. Small trout cower in the deep holes and logjams.
To flyfishers, the unique opportunity to hook a lifetime-class trout on a dry fly is presented. The catch: it will be in the dark.
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Floating a river in the profound dark of a moonless June night creates a strange memory. Without constant visual imagery for a framework, I'm left with non-linear flashing scenes, strobed into memory by a red LED headlamp or heat lightning, and woven together by sound, smell, texture, emotion, and sleep deprivation.
In mid-June the daylight lasts until well after 10 o'clock. We float downstream as the dusk completes -- by 11:30 the Au Sable River Valley is one of the darkest places in the continental United States. I lean back and look up through the tree-canyon walls, and am startled to find that the starscape has depth. My eyes falsely read the brighter stars as nearer to earth than the dim. It's dizzying. I return my gaze to the river and allow my pupils to readjust from the brightness of the stars, but still they strain against the blackness of cedar, Norway and white pine boughs in the absence of colored light. The seams and bubble lines absorb some starlight for relief from the obsidian water.
We pass another fisherman, not in a boat but sitting patiently on a cedar log, headlamp on low for safety as we pass. Pleasantries are exchanged in impossibly soft tones.
"Seen any bugs yet?"
"No, but I heard a riser just around the bend."
The dark swallows him and us again as we slip past. Solitude is immediate. The water gurgling around deadfalls and the faint rush of it against the hull of the wood boat add to the isolation by covering all but nearby or loud sounds. A healthy branch-crack from the woods; two barred owls conversing across the water; my own breathing. Finally, the dry-leaf rustling of an enormous insect passing in the dark; then another. Soon, a general raspy humming that implies thousands of Hexagenia limbata in the air around us.
And then the sound we are straining to hear: a big trout eating a fly. First is the wooden clap of his jaws, on each other or the water's surface, followed by the resonating plunge as he forces his bulk back below the surface.
The sound drifts to us from far downstream. As we move we use the white light to avoid a low-hanging cedar sweeper and in the five seconds of painful brightness so many Hexagenia limbata are attracted to it that I now have them on my shirt, in my collar, in my hair, on my hands. They are untouchably delicate and just moving around in the dark litters the boat with the dead and maimed.
The momentary white LED has burned the scene into the backs of my eyes: the air is thick with bugs, but there are few on the water. Good. My fly won't get lost among genuine examples when I cast. We slip downstream and drop the drag chain close to where we guess the rise was, and wait.
For some reason elapsed time is hard to estimate in the near-total dark, but eventually he rises again. It is shockingly loud -- I swear I hear jaw-snapping and tail cavitaion. Close, but still invisible. Seems to be less than two rod lengths away, alongside a log on the bank that, straining, I think I see. I have to wait for the adrenaline to clear from my bloodstream but I unhook my fly from its keeper and flick it a few feet upstream on the edge of the ghost-log. I can't see the drift, but the fish can. I hear the jaws close and I strike back. The rod doubles dangerously at this close range and the fish sounds under the boat.
He's not a fast-running fish but is strong and remains at depth, head-shaking, for a long time. In the hand he is heavy, with a wide, firm back and a deep, soft belly, full of Hexagenia limbata. We surrender to our eyes and indulge in white lights. Silver halos around black and red spots give way to bright goldenrod flanks. His jaw is hooked and scarred, his eyes reflective. Reptilian. A killer. A nightmare caricature of a daytime trout. After one searing flash photo he goes silently back into the opaque water.
This continues, though most fish do not eat on the first cast. Many do not eat a fly at all, though they continue rising to naturals as we cast ours over them. An hour, maybe, casting to the same fish. He might take it on the thousandth cast. Just have to get the perfect drift -- hard to do by feel.
At four in the morning a fog settles over the water and the stars begin to fade. The fish quit rising immediately, sulking to deep undercuts to digest for eighteen hours.
The morning after is missed -- slept through -- but the noon after suggests that it was all a dream. The river glows with sunlight, and slips by as always; small trout finning in the shallows. With the powerful visual stimulation before me the sounds, scents, and feelings of the night before seem imagined. The boat is littered with fly carcasses, natural and imitation. Hexagenia limbata, yellow-brown in life and white in the monochrome of the night before, is black in death.