Mayflies belong to the order Ephemeroptera, which refers to the short-lived nature of the winged adults. They are extremely important to fish diets and thus to fly fisher-men and -women. In some parts of the country, certain families are well-known because of their spectacular mass emergence. These coordinated emergences can clutter bridges and roads with mayfly bodies and make a mess of car windshields. Nearly all immature mayflies survive by eating detritus, diatoms, and other algae, and thus play a crucial role in decomposition in aquatic ecosystems. Mayflies are also valuable as biological indicators of water quality.
Ephemeropterans inhabit a diversity of aquatic habitats, which is reflected in the diversity of body shapes, behaviors, feeding strategies, and movement seen in this order. Generally, mayflies are either sleek and torpedo-shaped, minnow-like (swimmers) or robust or flattened clingers. Many of the clingers have evolved traits that help them hang on in fast water, such as gills or fine hairs for suction and extreme flattening of the body.
The Xerces Society details the status of a couple of at risk mayflies – the Lolo mayfly and the Moqui minnow mayfly – in the red list of aquatic invertebrates.