Naturespeak A naturalist's view of the world

June 24, 2007

An Explosion of Life

Filed under: Uncategorized — wykes @ 11:59 am

  Repeat after me: “Mayflies are good, Fishflies are Mayflies, Mayflies are Juneflies,  Juneflies are Goodflies.”  This message needs to be preached from the pulpits of life and the altars of everyday life. The annual hatch of these aquatic insects presents a story of eternal redemption. Yes, my brothers and sisters, Mayflies are harbingers of hope.  Alleluia, alleluia.

  Many of you probably already have “religion” when it comes to mayflies, but at the risk of preaching to the choir, it is important to embrace the subject.

  The first obstacle to overcome is what name to use when referring to “them.” Technically, I am referring to the species Hexagenia limbata, the Burrowing Mayfly (see here).  This is the species that emerges from Lake Erie in biblical numbers to cover every vertical surface within flight distance of the water. Although Mayfly is the proper name, they are better known as Fishflies.  Because this type emerges in June, and not May, they are also justifiably called Juneflies.  Our Canadian neighbors have been known to refer to them as British Soldiers and Fly Fisherfolk call them Golden or Michigan Mayflies. Our present concern is that far too many people call them a “nuisance.”

  The burrowing mayfly is the largest member of its clan – a collective of over 600 North American species in the order “Emphemeroptera.”  This order name literally means “wing for a day,” because mayflies “fly” for only a day or two out of their lives. Many of our kind only see them during this brief flight stage, so assume they are a short-lived creature whose sole purpose is to foul up our daily life. Actually our giant fishflies count their age in years, rather than the monthly or daily system used by most insects.

  The life cycle from egg to adult can take up to three years.  Burrowing Mayflies spend their developing years as aquatic nymphs.  The young are equipped with formidable tusks and powerful digging claws to construct “U” shaped burrows in the lake bottom. From the protection of this den they eat detritus and grow until they are about 2 inches long.  After a year or two (depending on the water temperature and habitat quality) the burrow gets to be a tight fit.  In late spring/ early summer, the fat nymphs wiggle to the surface, shed their old skin (and their gill breathing ways) to live their last 48 hours as an air breathing air flying adult.

  This aquatic life stage holds the key to their redemptive message. Mayfly nymphs can not live in polluted water.  Not so long ago, Lake Erie and the Detroit River were cesspools of pollution. Mayflies could not tolerate these conditions and virtually became extinct in the Western basin.  Fortunately, things changed for the better and by the 1990’s the insects began a dramatic comeback. Between 1991 and the current day, the Burrowing Mayfly population has grown at an exponential rate. The ever increasing hatches of these tiny messengers serve as an environmental indicator of improving water quality.

  A mayfly emergence can be a dramatic thing. It is not unusual to have a density 500 larvae per square meter of lake bottom, so you can imagine what it’s like when they come to the surface all at once. Take a look at this Doppler radar image of a large mayfly hatch coming out of the upper Mississippi River a year or two ago – it is a veritable explosion of life. Warm, muggy conditions will signal a communal night hatch. As the nymphs rise to the surface, they shed their old skin and fly to the shelter of shoreline trees or buildings.  This newly emerged individual is called a sub-imago or dun.  After resting over the course of the day, the sub-imago sheds its skin one more time to achieve the golden brown imago or spinner stage (see the cast off skin here).   At this point the adult is locked and loaded for mating.

  The setting sun at the end of the first (and only) day signals the final act.  Adult mayflies gather into huge hovering swarms near the waters edge. Individual flies commence to dance like tiny puppets pulled by invisible strings. They rise up several feet and then freefall the same distance. Two long “tail” streamers accentuate the motion and add to the dramatic presentation. Soon, a male and a female find each other and they join their abdomens in mid air. Locked in a mating embrace, the pair employs their duel wing power to journey over the open water.  The female then distributes her eggs over the surface and both of the lovers die.  It is in death that the cycle is completed.

  Many of the mayflies never make it to the Promised Land.  Instead, their lifeless bodies pile up in windrows at the Service Station – lured by the irresistible appeal of the bright lights. Since they have no mouths and can’t eat, they simply waste away their brief time.  Even in this seemingly hopeless situation, mayflies serve their most crucial role – they are food to innumerable birds and spiders.  In the water, they are the mainstay of the seasonal diet of fish as both nymphs and adults.

  Many Monroe old-timers will recall the phenomenal mayfly hatches they experienced prior to the mid-1940’s. They may not consider it a good memory, but at least it was part of everyday life. A generation has now grown up without that experience. Let’s hope that our present generation can view the current mayfly comeback as a signal of the redemption of a once broken lake. Spread the good word.

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