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.