Up from the Bottom

There are visitors to the screens of our lakefront porch this week. A number of mayflies and countless tiny midges cling to the screens and, for that matter, to the siding of the cabin. They’ve come up from the bottom of Birch Lake and up to our place, more than 75 feet back from the water and up a considerable hill.

One thing I know about mayfly hatches is that they don’t help the walleye fishing. But that’s not the main point of interest. Are mayflies hatching on your lake? Maybe you already know their story and where they come from, but in case you don’t, here it is.

Mayflies are insects that belong to the scientific order Ephemeroptera, a name no doubt chosen because these flies are ephemeral. The adults, with their triangular wings that propel them in silent flight in a posture that resembles a man with a jet backpack, live only two nights. They have no functioning mouthparts because they don’t eat – they have no need to. During their brief time in the air above a lake, male and female mayflies mate in swarms. The female deposits eggs as she flies low over the water or dips her abdomen. Some species (there are many) even submerge themselves and lay eggs underwater.

From eggs, mayflies develop into adults through several stages of molting. Different species have different molting stages, which also can vary with temperature and water conditions. The insects in immature stages swim to the surface or grab onto rocks or plants. There, according to the Texas A&M University Agri-LIFE extension website, they molt in minutes or second into winged subimagoes, which fly quickly from the water to nearby plants. There they molt again into adults (imagoes) that fly out over the water to begin the mating cycle anew.

Mayflies are the only group of insects that molt after they have wings, says the Texas A&M website. In all other insect orders, winged forms are found only as adults. A typical mayfly lifecycle lasts one year.

Immature mayfly stages have chewing mouthparts and feed by scavenging small pieces of organic matter, such as plant material or algae that accumulate on rocks or other surfaces. Mayflies require water relatively high in dissolved oxygen, which is why they thrive in fast-flowing trout streams. If your lake has mayflies, that’s one sign (certainly not the only indicator) that it’s in decent condition.  

So how did the mayflies affect the walleye fishing here on Birch Lake? Well, yesterday afternoon I caught two, one of them a 17-inch keeper that I brought back to join another already in the freezer as a fish fry for my wife and me. I put the fish in a landing net and set it on the pier while I moved my boat cover from the pier onto shore. Before I made it back to the net, the walleye flopped free and into the water. There went dinner.

Fishing was deadly slow last evening. Could be the mayflies, could be the east wind that brewed up, could be the Birch Lake gods working their will. Could be plain old angler ineptitude. There are too many variables on which to base a conclusion.