Mayfly

Suborder Schistonota
 Superfamily Baetoidea
   Siphlonuridae
   Baetidae
   Oniscigastridae
   Ameletopsidae
   Ametropodidae
 Superfamily Heptagenioidea
   Coloburiscidae
   Oligoneuriidae
   Isonychiidae
   Heptageniidae
 Superfamily Leptophlebioidea
   Leptophlebiidae
 Superfamily Ephemeroidea
   Behningiidae
   Potamanthidae
   Euthyplociidae
   Polymitarcydae
   Ephemeridae
   Palingeniidae
Suborder Pannota
 Superfamily Ephemerelloidea
   Ephemerellidae
   Leptohyphidae
   Tricorythidae
 Superfamily Caenoidea
   Neoephemeridae
   Baetiscidae
   Caenidae
   Prosopistomatidae

Mayflies are insects which belong to the Order Ephemeroptera (from the Greek ephemeros = "short-lived", pteron = "wing", referring to the short life span of adults). They have been placed into an ancient group of insects termed the Paleoptera, which also contains the dragonflies and damselflies. They are aquatic insects whose immature stage (called naiad or, colloquially, nymph) usually lasts one year in fresh water. The adults are short-lived, from a few hours to a few days depending on the species. About 2,500 species are known worldwide, including about 630 species in North America. Common names for mayflies include "dayfly", "shadfly", "Canadian soldier", and "fishfly" .

The mayfly belongs to group 1 taxa, or pollution–sensitive animals. This means if mayflies are in or around the water, the water should be good quality, perhaps even good enough to drink without distilling or boiling.