Nature Bulletin No. 345-A May 17, 1969
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
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
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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Update: June 2012