Short Key to Mayfly Genera

This simple key permits the easy identification of mayfly nymphs and adults down to the genus level. Identification of the exact species is more difficult, often requiring the use of a microscope. To use this key simply start at the top and select the appropriate member of the pair. (ie nymph or adult). If a number follows your choice, go to that number and choose one of that pair (and so on). If a name follows your choice (ie Ephemeridae) you have identified the Family to which your insect belongs. Click on this name and proceed in the same manner to identify the genus to which your insect belongs. Click on the genus name to read a brief description of the genus and some of the most common species. (I am still writing this last part, so please be patient.)

Links will be provided to illustrate and explain the technical terms.

INSECT STAGE
Nymph

Adult






 
NYMPH FAMILY KEY
1. Legs flanged for burrowing; 
   mandibles bearing long tusks---------------------Ephemeridae
1. Legs cylindrical or flattened in cross-section; 
   mandibles without long tusks---------------------2





2. Gills of abdominal segment 2 operculate, 
   almost entirely covering remaining gills---------Caenidae 
2. Gills of abdominal segment 2 absent or, 
   if present, not operculate-----------------------3




3. No gills on segments 1-2 (in some cases, 1-3)----Ephemerellidae
3. Gills on segments 1-7 or 1-6---------------------4





4. Gills on segments 1-6 (largely concealed by
   carapacelike extension of mesonotum)-------------Baetiscidae
4. Gills on segments 1-7----------------------------5






5. Body strongly flattened; 
   eyes on dorsal surface of head-------------------Heptageniidae
5. Body not strongly flattened----------------------6






6. Tails clothed with short hairs on both sides-----Leptophlebiidae
6. Outer pair of tails with hairs on inner
   (mesal) sides only-------------------------------7






7. Front tarsal claw double-------------------------Ametropidae
7. Front tarsal claw single-------------------------Baetidae





 
NYMPH GENERA KEY
EPHEMERIDAE
1. Frontal prominence of head deeply forked---------------------------Ephemera
1. Frontal prominence of head rounded---------------------------------Hexagenia





CAENIDAE
1. Operculate gills of abdominal segment 2 triangular-----------------Tricorythodes 
1. Operculate gills not triangular------------------------------------2





2. Operculate gills with inner margins overlapping,
   outer margins rounded; head with prominent tubercules--------------Brachycercus
2. Operculate gills nearly rectangular, not overlapping 
   at inner margins; head without tubercules--------------------------Caenis





EPHEMERELLIDAE
This family contains but one common genus-----------------------------Ephemerella





BAETISCIDAE
This family contains but one genus------------------------------------Baetisca





LEPTOPHLEBIIDAE
1. Gills of abdominal segment 1 deeply cleft, of segments
   2-7 broad, platelike, with long apical extensions------------------Leptophlebia
1. Gills of abdominal segments 1-7 alike, deeply cleft----------------Paraleptophlebia





BAETIDAE
1. Gill tufts at base of maxillae and at foreleg bases---------------Isonychia
1. No gill tufts at base of maxillae or foreleg bases----------------2





2. Posterolateral angles of abdominal segments prolonged
   as thin, flat spines----------------------------------------------Siphlonurus
2. Posterolateral angles of abdominal segments not
   prolonged as spines-----------------------------------------------3

3. Gills single------------------------------------------------------4
3. Gills double or, if single, bearing a recurved flap---------------6





4. Hind wing pad absent----------------------------------------------Pseudocloen
4. Hind wing pad present---------------------------------------------5





5. Middle tail as long as outer tails--------------------------------Centroptilum
5. Middle tail shorter than outer tails------------------------------Baetis





6. Hind wing pad present---------------------------------------------Callibaetis
6. Hind wing pad absent----------------------------------------------Cloen





AMETROPIDAE
1. Maxillary palp two-segmented--------------------------------------Metretopus
1. Maxillary palp three-segmented------------------------------------Siphloplecton





HEPTAGENIIDAE
1. Gills of abdominal segment 7 slender, fingerlike------------------Stenonema
1. Gills of all segments platelike-----------------------------------2





2. Gills of abdominal segments 1 and 7 enlarged, each pair
   converging beneath the abdomen to form, with other gills,
   an adhesive disk--------------------------------------------------Rithrogena
2. Gills in normal position, not modified as above-------------------3




3. Tails two---------------------------------------------------------Epeorus
3. Tails three-------------------------------------------------------Heptagenia





 
ADULT FAMILY KEY
1. Lateral ocellus nearly one-half as large as compound eye-----Caenidae
1. Lateral ocellus only one-tenth to one-fourth
   as large as compound eye-------------------------------------2





2. Abdominal segments 6 and 7 wider, longer, and higher
   in profile view than segments 5 and 8------------------------Baetiscidae
2. Abdominal segments 6 and 7 not wider, and not higher
   in profile view than segments 5 and 8------------------------3





3. Hind tarsus with 5 clearly differentiated, movable segments--Heptageniidae
3. Hind tarsus with only three or four clearly
   differentiated segments--------------------------------------4





4. Vein MP2 of fore wing sharply bent near the wing base,
   running parallel with CuA in this area-----------------------Ephemeridae
4. Vein MP2 not bent, not parallel with CuA near wing base-------5





5. Fore wing with one or two long intercalary veins between
   MP2 and CuA---------------------------------------------------Ephemerellidae
5. Fore wing without long intercalary veins between MP2 and CuA--6





6. Tails three--------------------------------------------------Leptophlebiidae
6. Tails two (middle tail vestigial)----------------------------7

7. Fore wings with one or two pairs of long parallel cubital
   intercalary veins and without free marginal veinlets---------Ametropidae
7. Fore wings with either a series of short, slightly sinuate
   veinlets bewteen CuA and inner margin of wing, or with one 
   or two long, basically detached cubital intercalary veins
   accompanied by free marginal veinlets------------------------Baetidae





 
ADULT GENERA KEY
EPHEMERIDAE
1. Wing membrane heavily spotted--------------------------------Ephemera
1. Wing membrane not spotted------------------------------------Hexagenia





CAENIDAE
1. Crossveins numerous; male claspers three-segmented,
   the last sement rounded--------------------------------------Tricorythodes
1. Crossveins very few; male claspers one-segmented,
   sharply pointed----------------------------------------------2





2. Prosternum twice as broad as long;
   bases of forelegs widely separated---------------------------Brachycercus
2. Prosternum twice as broad as long;
   bases of forelegs close together-----------------------------Caenis





EPHEMERELLIDAE
Family contains but one common genus----------------------------Ephemerella





BAETISCIDAE
Family contains but one genus-----------------------------------Baetisca


LEPTOPHLEBIIDAE
1. Length, 10-12 mm; body robust--------------------------------Leptophlebia
1. Length, 4-8 mm; body slender---------------------------------Paraleptophlebia





BAETIDAE
1. Gill remnants present on base of forelegs--------------------Isonychia
1. Gill remnants absent-----------------------------------------2





2. Hind tarsus with five segments-------------------------------Siphlonurus
2. Hind tarsus with four well-defined segments------------------3





3. Both fore and hind wings with numerous crossveins------------Callibaetis
3. Fore wing with few crossveins; hind wing, if present,
   with few or no crossveins------------------------------------4





4. Hind wind present--------------------------------------------5
4. Hind wing absent---------------------------------------------6





5. Marginal veinlets of fore wing single------------------------Centroptilum
5. Marginal veinlets of fore wing in pairs----------------------Baetis





6. Marginal veinlets of fore wing single------------------------Cloen
6. Marginal veinlets of fore wing in pairs----------------------Pseudocloen





AMETROPIDAE
1. Fore wing with one pair of cubital intercalary veins;
   wing membrane unspotted--------------------------------------Metretopus
1. Fore wing with two pairs of cubital intercalary veins;
   wing membrane spotted----------------------------------------Siphloplecton
 




HEPTAGENIIDAE (males only)
1. First segment of fore tarsus as long as second, or longer----Epeorus
1. First segment of fore tarsus shorter than second-------------2





2. Crossveins in stigmatic area of fore wing joined 
   in a network-------------------------------------------------Rithrogena
2. Crossveins in stigmatic area of fore wing not joined 
   in a network-------------------------------------------------3





3. Penes more or less L-shaped----------------------------------Stenonema
3. Penes not L-shaped-------------------------------------------Heptagenia