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Mayflies have been around eons. They can be dated back to before the dinosaurs. Their presence indicates that the water they inhabit is free of harmful chemicals, and that it is a healthy environment. Adult mayflies only live long enough to mate and lay their eggs. They can be found in fast streams, like City Creek, clinging to rocks, algae, and leaf debris in the water.


Mayfly development can be divided into three stages: nymph, dunn, adult.

Mayfly larvae are called nymphs. They generally have three tails (anal circi), gills on their abdomen, and only one claw on each leg. Nymphs may molt as many as 50 times, although most do not do it that often. Breathing takes place with the gills, which, in some species, can be moveable or able to vibrate. This increases the amount of water moving over them to aid in oxygen absorption.

In some species, the nymph may mature within a few months, while in others maturation can take up to two years. During this stage, the mayfly under goes metamorphosis, changing its structure to that of the adult with flying wings. Most nymphs live in the aquatic vegetation or among dead leaves and vegetation, but some can burrow into substrates. Some cling to undersides of rocks to prevent being swept away by the stream. Although some nymphs are omnivorous, most are herbivores feeding on algae, diatoms, and detritus.

Emerging from the nymph is the dunn. It looks like an adult, having wings. It differs from the adult in the fact that it has very small hairs on the wings. It flies to a nearby tree or bush to harden its skin and dry its wings. This could take 1-2 days.
The goal of the adult stage is merely to mate. This stage can last from a few hours, to a few weeks. The adult cannot eat because it does not have functional mouth parts or a digestive system. All of its nutrients must come from food stored during the nymph stage.

Mating takes place by the male using his legs to attach to the female. They copulate and the male flies off to die. The female then flies to the water and places her eggs on the surface. After depositing her eggs the female dies, or is eaten by a fish. Anywhere from 2,200 to 8,000 eggs may be produced.


•antennae are short and bristle-like
•4-9 pairs of leaf-like gills
•3 long filaments at rear of abdomen

•2 large, upright front wings
•Small triangular hind wings
•2 or 3 tails
•Short and bristle-like antennae
•Males front legs are longer in order to hold on to the
female in flight
•Have smaller mouths because most
do not eat
•Short life span (2 hours to 14 days)
•Adults have a pale yellow body with brownish
stripes, and a reddish brown mid-segment


If many mayflies are found in a stream it could be a sign that the stream may be eutrophic. The nymph thrives on the extra nutrients created by eutrophication and algal overgrowth, which is caused by sewage, manure, and fertilizers. By feeding on these substrates, though, the mayfly also aids in removing them and returning them to the terrestrial environment. Through respiration they release carbon back to the air and phosphorous and nitrogen are taken in to their bodies from their food source (leaves and algae).

Mayflies are also an important food source for other organisms in the creek. They are fed on by fish, such as the trout, and by birds, such as the American Dipper. Mayflies are even a source of food for terrestrial insects, like spiders that capture them by the thousands.

Sport fishermen use artificial lures that simulate both the juvenile larvae (wet flies) or the reproductive winged adults (dry flies).

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