Sometimes the best way to appreciate our fleeting and miraculous existence on this planet is to study creatures whose brief lives seem so very different from our own. Nothing seems so far removed from the life of a human being than that of the mayfly, a tiny insect that spends a year or more underwater as an aquatic larva, or nymph, before emerging to live only for a day or two, sometimes only a few hours, as a winged adult. Yet a mayfly, at each stage of its life cycle, is inextricably linked to us, as every person who fishes for trout knows.
The same cool mountain streams in the Catskills and Hudson Valley where native brook trout spawn and thrive are also habitat for the trout’s favorite food, the aquatic insect larvae, or nymphs, of stoneflies, caddisflies, and mayflies. This of course is no mere coincidence, but part of the way the natural world works. Brooks well shaded by the trees, especially hemlocks, that grow along their banks, run clear and cold, and thus have the high oxygen levels required by both the trout and their prey. It’s pure chemistry: oxygen is more soluble in cold water. Cut down those trees, and sunlight warms the water, diminishing its dissolved oxygen, and with it the populations of trout and the mayflies and other aquatic insect larva they feed upon.
Fly fishing is an art as well as a science, and expert anglers know how to tie artificial lures from deer or muskrat hair, feathers, and other materials that serve as elegant imitations of the insects, such as mayflies, that trout eat. To find mayfly nymphs, one need only scoop some of the small stones or leafy debris from the bed of a trout stream with a small net or strainer. Empty the strainer into a pan of water, and you will start to see tiny wriggling creatures emerge from it. Mayfly nymphs of different species have six legs, like all insects, and two or (more often) three hairlike tails, but lack the long antennae of stoneflies. With the naked eye, or even better with a hand lens, you will be able to see seven pairs of leafy gills along the abdomen of a mayfly nymph. These external gills are constantly fluttering with a wavelike motion, to increase the flow of oxygen-rich water over them.
Although some species of mayflies emerge as flying adults in summer, a few even in fall, most “hatches” of these graceful insects take place in May, the month they are named for. Mayflies are unique among insects in that they require two molts to complete the final stage of their metamorphosis into adulthood. After the first of these molts, the sub-adult (called a “dun” by fly fishers) is milk-white, and seen only briefly in the air as it flies to a nearly tree or shrub. Within hours the new adult molts again for the last time, and soon takes to the air again upon slender, beautifully patterned wings.
If you are lucky enough to be bankside some May evening, when the air is still and the stream’s pools glint like gold in the low sun, you may witness one of spring’s loveliest spectacles, the courtship flight of hundreds or even thousands of newly emerged mayflies over the water. These insects swarms bob up above the stream’s surface in a kind of rhythmic aerial dance. After mating occurs and eggs are laid on the water, the cloud of mayflies disperses. Within a few hours, or at most a day or two, their brief lives are over, their sole task as adults having been completed. Mayfly nymphs spend months or even years in streams, feeding mostly on diatoms and other tiny plants filtered from the water, or gathered or scraped from the stream bed (depending on the species). Then they metamorphose into winged adults that do not eat at all during their brief existence – adult mayflies don’t even have mouths.
The scientific name that includes all kinds of mayflies is Ephemeroptera, whose ancient Greek root is the same as that of our English word, ephemeral. These delicate insects are fitting emblems of the beauty and transience of mortal life, whether it is measured in hours or in decades. To borrow a phrase from the ancient Greek poets, all creatures, including human beings, are in a sense just “creatures of a day.” Any thoughtful person, reflecting upon this truth, is likely to feel a heightened sense of kinship with even the humblest things, like mayflies.
Richard Parisio is a lifelong naturalist, educator and writer. He currently leads field trips for school classes at Mohonk Preserve, teaches courses about John Burroughs and conducts tours of Slabsides and the John Burroughs Sanctuary for groups and individuals by request. Rich is New York State coordinator for River of Words, a national poetry and art program on the theme of watersheds, and teaches River of Words programs for school classes, grades K-12, by request. Contact Rich (firstname.lastname@example.org) with questions, comments, or suggestions for Nature at Your Doorstep.