Ept-index
Guides
Caenis
Common Square-gills
Caenis is a genus of small mayflies in the family Caenidae, commonly known as "square-gilled mayflies." Adults are among the smallest mayflies, with some species measuring only 3–4 mm in body length. The genus is globally distributed across multiple continents and serves as an indicator taxon for aquatic ecosystem health. Nymphs inhabit various freshwater environments, and adults emerge in synchronized events.
Callibaetis pictus
Speckled Dun
Callibaetis pictus is a small minnow mayfly in the family Baetidae, commonly known as the Speckled Dun. It is distributed across Central America and North America, including all of Mexico and the northern and southwestern United States. Like other mayflies, it has an aquatic nymphal stage lasting months to years, followed by a brief adult lifespan measured in hours to days. The species is part of the EPT index (Ephemeroptera, Plecoptera, Trichoptera) used to assess water quality in environmental monitoring.
Ephemeridae
Burrowing Mayflies
Ephemeridae is a family of large mayflies comprising approximately 150 described species distributed worldwide except Australia and Oceania. Adults range up to 35 mm in length and possess either two or three elongated caudal filaments. Many species exhibit distinctively patterned wings. The family is commonly known as "burrowing mayflies" due to the fossorial adaptations of their nymphs, which inhabit silty or sandy substrates in freshwater systems. Nymphs possess specialized morphological features including spur-like projections on foretibiae, dorsally positioned plumose and lanceolate abdominal gills, and mandibular tusks that facilitate burrowing behavior.
Hexagenia atrocaudata
Lake Hex
Hexagenia atrocaudata is a burrowing mayfly species in the family Ephemeridae, known from North American lakes and rivers. As a member of the common burrower mayflies, it spends the vast majority of its life as an aquatic nymph in bottom sediments, emerging as a short-lived winged adult for reproduction. Adults lack functional mouthparts and do not feed. Mass synchronous emergences can occur, producing swarms that attract fish and anglers alike. The species serves as an important indicator of clean freshwater ecosystems and provides substantial food resources for aquatic and terrestrial predators.
Isonychia bicolor
mahogany dun
Isonychia bicolor, commonly known as the mahogany dun, is a species of brushlegged mayfly in the family Isonychiidae. It is found in southeastern Canada and the eastern United States. Like all mayflies, it undergoes incomplete metamorphosis with aquatic nymphal stages and short-lived winged adults. The species is part of the EPT (Ephemeroptera-Plecoptera-Trichoptera) biological index used to assess water quality.
Plecoptera
stoneflies
Plecoptera, commonly known as stoneflies, comprises approximately 3,500 described species worldwide. This order represents one of the most primitive groups of Neoptera, with fossil relatives dating to the Carboniferous and Lower Permian periods, though modern diversity appears to be of Mesozoic origin. Stoneflies are found on every continent except Antarctica, with distinct populations in the Northern and Southern Hemispheres. All species are aquatic in their immature stages and are highly sensitive to water pollution, making them important bioindicators of stream and river health.