General: The Mayflies (Class Insecta, Order Ephemeroptera) are a diverse group of small aquatic insects with almost 650 species in North America and perhaps 75 in Nevada, including about four species in arid southern Nevada. Mayflies are sensitive to pollution, so if you find them near a body of water, you know the water quality probably is good.

Mayflies spend most of their lives as aquatic immatures, called nymphs. Nymphs are small creatures with three long tail bristles and gills along the side of the abdomen. Nymphs crawl around on the bottom of ponds and streams. Adult mayflies are recognized by the two large, membranous wings held upright and their two long tail bristles.

Mayflies can spend a year as a nymph, then only spend 30 minutes to a day as a breeding adult.

Isonychia intermedia is known from the Muddy River area. Choroterpes inornata and two other species should be found around Las Vegas.