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Mayflies
Nature Bulletin No. 345-A    May 17, 1969
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

MAYFLIES
Back in the time of Aristotle, the Greeks applied the name Ephemeron to an insect we know as the Mayfly, because it lived only a single day. Actually, altho the winged adult may die the same day it matures, the young which produces it must go through an underwater existence ranging from several weeks to two years, depending on the species. The Greek name was quite apt, however, because the adult mayfly is a delicate defenseless creature with a pair of gauzy triangular wings held upright when at rest, and a smaller second pair which are often overlooked. The soft slender body varies in length from one-quarter inch in the smaller kinds to one and one-half inches in the larger ones, and is tipped with two or three bristle-like tails, often twice as long as the body, which small boys mistakenly call "stingers".

Mayfly eggs hatch into water-dwelling six-legged larvae with seven pairs of gills. Some species, the "sprawlers", are flattened and streamlined for clinging to rocks in swift streams. Another group, the "clamberers", are found among weeds in the quiet water of lakes or stream pools and, because they are out in the open, make an important part of the diet of fish. A third group, the "burrowers", are large larvae reaching two inches or more in length and living in soft bottom muds where they slowly tunnel through the mucky silt -- literally "eating" their way, like earthworms. These are often dredged up and sold as bait, called "wigglers", especially to ice fishermen seeking perch and bluegills.

Adult mayflies, with only feeble imperfect mouthparts, do not eat but all mayfly larvae have chewing mouthparts by which they feed on algae and other plant material, both alive and dead. As these larvae approach maturity they become hunchbacked from the swelling wing pads beneath the outer skin, and increasingly restless. Finally they swim or crawl to the surface. There, the skins of some species split so swiftly that the adults almost explode from their juvenile husk; others must struggle for several minutes to free themselves.

Mayflies are unique in that the winged adult passes through another molt before it becomes fully mature. Emerging from the water, they fly to some nearby tree, bush or other shelter where they rest for a day or more, depending on the weather, before this final molt. Then these "duns", as fishermen call them, shed their dull gray skin and appear in colors ranging from pure white, through shades of yellow, green, brown and red to almost black. On that day, as evening approaches, they go through their mating flights, lay their eggs -- and die.

Some kinds dive to drop their eggs on water; others drop them from high in the air; while still others light on the surface to lay their eggs. In many trout streams unusually good fly fishing for brown trout can be had when certain of the large burrowing mayflies swarm and go through their brief performance.

Mayflies are found in most parts of the United States but are more abundant and show a greater variety of kinds in the Great Lakes region. They are food for many birds, bats, toads and dragonflies, as well as fishes. Many artificial flies used by anglers are imitations of the mayfly. Different species hatch at intervals from March to November but along our Chicago lake front the largest swarms appear about the first of July. Then they flock to street lights and store windows at night, often forming heaps a foot or more high and making pavements dangerously slick with their crushed bodies.

Immortality awaits an ode to Ephemeron.


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