Caenidae

Caenidae nymphs possess distinctive square or rectangular gill plates (lamellae) on abdominal segments I-VII, a key family-level character. Adults have reduced mouthparts and forewings with simplified venation compared to other Ephemeroptera. The family is distinguished from Baetidae by the presence of gills on abdominal segment I and the square gill shape. Small body size (often under 10 mm) and association with silty substrates further separate them from most other mayfly families.

Freshwater aquatic environments, primarily lotic (flowing water) systems with depositional zones and quiet to stagnant water. Nymphs inhabit silty bottoms, sand, and fine sediments. Found in streams, rivers, lakes, and ponds with organic-rich substrates.

Cosmopolitan distribution with records from all continents except Antarctica. Documented from North America (including Vermont, USA), South America (Argentina, Brazil, Colombia, Bolivia, Ecuador, Peru, Uruguay, Venezuela), Europe (Denmark, Norway, Sweden), Asia (India, Thailand, Vietnam, Indonesia, Taiwan), and Australia (Western Australia, Northern Territory, New South Wales).

Hemimetabolous development with egg, nymph, and adult stages. Voltinism varies: multivoltine life cycles with overlapping generations documented in some species (e.g., Caenis latipennis with four generations). Egg development requires accumulated degree days (132 degree days reported for C. latipennis). Nymphal development spans multiple instars (five development classes described in C. latipennis). Parthenogenesis documented in at least Caenis cuniana. Adults are short-lived; females of C. latipennis complete emergence, mating, and oviposition in approximately 37 minutes.

Nymphs are sprawlers—flattened body form adapted for clinging to substrates in silty environments. Adults exhibit extended emergence periods with multiple peaks. Rapid adult reproductive behavior with brief terrestrial phase.

Important components of freshwater food webs as prey for fish and other aquatic predators. Secondary production documented at 6,052.57 mg/m²/year in C. latipennis populations. Contribute to nutrient cycling and energy transfer in depositional zones of aquatic ecosystems.

• BaetidaeSimilar small body size and habitat preferences, but distinguished by absence of gills on abdominal segment I and oval/rounded gill shape versus square gills in Caenidae.
• EphemerellidaeOverlap in lotic habitats; Caenidae separated by smaller size, square gills, and preference for silty substrates versus cleaner gravels.

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• First record of the nymph of Caenis cuniana Froehlich, 1969 (Caenidae: Ephemeroptera) and new distributional records of Caenidae from Colombia
• Life History and Secondary Production of Caenis latipennis Banks (Ephemeroptera: Caenidae) in Honey Creek, Oklahoma
• New distributional records and life stage description of Caenis species (Ephemeroptera: Caenidae) from Brazil
• Distribution extension of Oriental mayfly Clypeocaenis oligosetosa Soldán, 1983 (Ephemeroptera: Caenidae)
• A new species of Caenis Stephens, 1835 (Ephemeroptera: Caenidae) from Tamil Nadu, Southern India
• Life Cycle and Annual Production of Caenis sp (Ephemeroptera, Caenidae) in Lake Escondido (Bariloche, Argentina)
• Description of Alloretochus sigillatus new species with comments and new distributional records for Alloretochus peruanicus (Ephemeroptera, Caenidae, Brachycercinae)
• South American Caenis Stephens (Ephemeroptera, Caenidae), new species and stage descriptions
• First records of small squaregilled mayflies (Ephemeroptera, Caenidae) from the state of Roraima, Northern Brazil
• Wundacaenis , a new genus of Caenidae (Insecta : Ephemeroptera) from Australia
• New record of Caenis nigropuctatula Malzacher, 2015 (Ephemeroptera: Caenidae) from Southern India