Mayflies are insects belonging to the scientific family Ephemeroptera. There are roughly 2000 species in total, most living in near bodies of fresh water. When present in an ecosystem, they tend to be extremely abundant, to the point of being considered pests. In areas such as Detroit and Windsor, on the shores of Lake Erie, there have been instances when the carcasses of mayflies have been so abundant that snow plows were required to clear the roads.

These animals are interesting from both a biological and human perspective. They spend the majority of their lives in the larval state, living in the benthic zones of lakes. They are soft bodied, and of relatively large size (on the order to 1-3 centimeters in length). The adult stage of the mayfly's life is very short; often as short as a few hours. Each species takes cues from the environment in order to emerge simultaneously, and metamorphose into adults for the express and sole purpose of mating. In fact, most species have no formed mouth parts, as their life expectancy as adults is so short that they do not feed after emergence. The normal time of emergence is in the month of May in most temperate climates (hence the name), and the animals tend to emerge at dusk. They reproduce while flying (most of the time), and after mating females will fall to the water to lay their eggs. The scene either on or near lakes after an emergence and mating event is true carnage; bodies often cover nearly every square meter of the surface.

Mayfly populations have suffered immense declines in abundance over the past century, due primarily to two factors. First, human development on the shores of lakes often results in eutrophication of these systems, which leads to an impoverishment of the benthic habitat. In fact, in many systems the mayfly has become extinct as a direct result of eutrophication. Second, humans tend to put up lots of very bright lights around lakes, which confuses the highly adapted navigational system of the mayfly. Often, lamp-posts and houses may become centers of mayfly reproduction, and the animals may successfully breed. However, after mating the females will fall to the ground rather than the surface of the water, and the eggs will be deposited and subsequently lost.

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