Mayflies Mayflies Order - Ephemeroptera Source of Name - The month of May is a predominant time for their hatching. There are approximately 2000 species of mayflies in the world, 700 in North American and Mexico. Scientists figure that mayflies have been around for 270 million years and haven't changed much. Mayflies have the longest history and association with the sport of fly fishing. A mayfly is the only aquatic insect with a 2 stage winged metamorphosis. This is called an incomplete metamorphosis which means that the life cycle, which usually lasts a year, consists of only 3 stages (egg, nymph, and adult). They do not have a pupal stage. A mayfly lives underwater as a nymph until they reach maturity and then they hatch into winged adults called duns. The dun molds and is now called a spinner. The spinner mates and then dies, but before dying the females lay eggs in the river. A mayfly adult has a brief life, usually only a day or two. The nymphs have one pair of wing pads, gills on their abdomen, and two or three very long visible tail filaments. It goes through 20 to 30 molts as it grows, between the last few molts the wing pads develop and darken. A mayfly nymph is often divided into four major groups based on the nymph's behavior. The groups are: crawlers, clingers, swimmers and burrowers. A crawler spends their underwater life crawling between rocks and pebbles. Their abdomen is oval with forked gills along the top and side and most species have tusk like mandibles. They have a slightly slightly flattened body and head. Its head is equal to or less than the width of their abdomen and they have three tails. A clinger is a very flat mayfly, they have two tails, live in fast water and rarely lose their grip on the bottom. You will recognize them by the size of their head, as it is wider than its abdomen. A swimmer has a round streamline body with a head equal to or less than the width of its abdomen. The abdomen has oval gills along its sides and a tail with fringed, interlocking hairs that form a paddle like tail (they swim like a dolphin). Swimmers are the most widely distributed mayflies and are found in all fishable habitats. Last is the burrower which dwells in sediment soft enough to burrow holes into but not so soft that their tunnel will easily collapse. They have a long, oval shaped body with fringed gills, two tails, and visible tusk like mandibles. The nymph struggles through the water column to emerge. It emerges to the water's surface where they turn into a dun and float on the surface until their wings dry. This is the first adult stage of a mayfly, also called a subimago. After its wings dry they fly to the trees or bushes along the stream where they molt and turn into spinners, this process takes as little as an hour or as much as three days. The dun stage of a mayfly generally has two to four triangular wings with numerous veins, well developed eyes, small antennaes, long forelegs, and cloudy upright opaque wings that are usually brownish to grayish in color. The spinner or imago is a sexually mature adult mayfly with clearer wings, longer tail filaments and brighter colors than duns. This is the mayfly's mating stage. The females do not have working mouth parts, they are meant for reproduction only. After molting to the spinner stage the males congregate in swarms above the water, when a female flies into the swarm she is seized by a male and the mating takes place in flight. The females then deposit their eggs in one of three ways (depending on the species). They either land on the water's surface to deposit their eggs, drop the eggs from the air, or crawl under the water and attach them to the substrate. The eggs are covered in a sticky substance that lets them attach to the bottom of the river.
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