Order Ephemeroptera (Mayflies)
Courtesy of the Cacapon InstituteWing pads may be present on the thorax; three pairs of segmented legs attach to the thorax; one claw occurs on the end of the segmented legs; gills occur on the abdominal segments and are attached mainly to the sides of the abdomen, but sometimes extend over the top and bottom of the abdomen; gills consist of either flat plates or filaments; three long thin caudal (tails filaments) usually occur at the end of the abdomen, but there may only be two in some kinds. 

Swimming mayflies


Ameletidae (Ameletid minnow mayfly): Comb of stiff spines on the mouthparts; gills have a dark, sclerotized (hard) band along the outside edge; antennae are shorter than twice the width of the head; usually have dark bands on the tail and alternating dark and light on the abdomen. Swimmer/clinger; Collector/gatherer; VS-M (L)(F) [Adult]


Baetidae (Small minnow mayfly): Antennae two times longer than the width of the head; gills variable in shape and attached at abdominal segments one through seven; two or three caudal (tail) filaments. Swimmer; Collector/gatherer; VS-M (M)(F/S) [Adult]


Isonychiidae (Brush-legged mayfly): Forelegs have a double row of hairs; gills oval shaped and present on abdominal segments one through seven; long hairs on the margins of the caudal filaments. Swimmer/crawler; Collector/gatherer; S-M (L)(F) [Adult]


Siphlonuridae (Primitive minnow mayfly): Antennae less than two-time the width of the head; gills usually oval shaped and present on abdominal segments one through seven; long setae on the caudal filaments. Swimmer; Collector/gatherer; S-M (L)(F/S) [Adult]

Clinging/crawling mayflies


Caenidae (Square-gilled mayfly): Gills on the first abdominal segment very small; gills on the second segment operculate (plate-like) covering much of the remaining gills. Clinger/crawler; Collector/gatherer; VS-S (M)(F/S) [Adult] 


Ephemerellidae (Spiny crawler mayfly): Gills present of the first abdominal segment but absent from the second; gills usually present on the remaining segments; two or three caudal filaments. Clinger/crawler; Collector/gatherer; VS-M (L)(F) [Adult]


Heptageniidae (Flatheaded mayfly): Body, head and legs are flattened (femora); gills present on abdominal segments one through seven; usually three caudal filaments, but some may have two. Clinger; Scraper; S-M (L)(F) [Adult]


Leptophlebiidae (Prong-gilled mayfly): Gills on abdominal segments two through seven forked and variable in shape; gills on the first segment finger-like; short hairs usually cover the caudal filaments. Clinger/crawler; Collector/gatherer; VS-M (L)(F) [Adult]


Tricorythidae (Stout crawler mayfly): Gills absent from abdominal segment one; gills on segment two are (operculate), plate-like triangular or oval shaped and conceals gills on segments three through six. Clinger/crawler; Collector/gatherer; VS-M (M)(F/S) [Adult]

Burrowing mayflies


Beatiscidae (Armored mayfly): Top portion of the thorax is fused and coves most of the abdomen concealing the gills; caudal filaments are short and fringed with hairs. Burrower/crawler; Collector/gatherer; VS-M (M)(F) [Adult]


Ephemeridae (Burrowing mayfly): Has upturned mandibular tusks; head and front legs slightly widened and are used for burrowing; gills on the upper abdominal segments are small and the remaining gills are forked with fringed margins (feathered) and held over the top and sides of the abdomen. Burrower; Collector/gatherer; M-L (M)(S/F) [Adult]


Potamanthidae (Hackle-gilled mayfly): Mandibular tusks present; front legs slender, not modified for burrowing; gills on segment one small, gills on remaining abdominal segments are feathery. Burrower; Collector/gatherer; S-M (M)(S/F) [Adult]