Ephemeroptera (Mayflies)
All mayfly species have aquatic larvae and short-lived terrestrial adults. The primitive characteristics of the group are an inability of the adult to fold their wings flat when at rest. Instead they are held straight above the body. Although mayfly adults are rather uniform in structure, larvae exhibit a wide variety of morphologies: the bodies of active swimmers are streamlined, while those that tend to cling to rocks are dorsoventrally flattened. Burrowing mayflies have cylindrical bodies with mandibular tusks and broad forelimbs for digging. Larval gills are filamentous or plate-like (more or less oval or heart-shaped), and may be arranged singly or doubly.
Here is a flow chart that uses 'key' features to identify mayflies to family level.
This guide is intended as an aid to the identification of mayfly larvae in Hong Kong by comparison of their morphological differences under a dissecting microscope (50x). However there are several instars throughout larval stage, and the distinctive features might not be evident until the later stages. This website shows different sizes/instars of larvae of as many as species possible. Some individuals need to be dissected to show details of their mouthparts under a compound microscope (200x). Identification can be difficult because of loss of body parts (e.g. gills or legs are fragile), but mouthparts (on the head) tend to remain intact, and can be a good indicator for species identification.
An identification guide to Hong Kong mayflies:
Prosopistomatidae
The family comprises a single genus Prosopistoma. The total number of species globally is about 44.
Distribution (Global map): found in Africa, the Middle East, India, Oriental region and Australasian region.
Features for ID | Scientific name |
Body size small, about 3mm long, oval shaped like a beetle Pronotum and mesonotum fused to form a hemispherical carapace, with gills I - VI concealed beneath it Three feathery cerci mostly retracted into body |
Prosopistoma sinense |
Ephemeridae
It presently includes 96 species in 7 genera and 2 subfamilies (Ephemerinae & Hexageniinae)
Distribution: these burrowing mayflies are almost cosmopolitan, but not yet found in Australia and the oceanic islands.
Features for ID | Scientific name |
Frontal process concave anteriorly (bifurcate) | |
Mandibular tusks asymmetrical, right tusk reduced about 3/5 length of left tusk |
|
Ephemera pictipennis | |
Mandibular tusks symmetrical, right tusk slightly shorter than left tusk |
|
--> Length of frontal process subequal/shorter than width |
|
Ephemera spilosa | |
--> Length of frontal process subequal/longer than width |
|
Ephemera serica | |
Frontal process rounded Mandibular tusks symmetrical and subequal in length |
|
Undescribed sp. |
Baetidae
The most specious family of Ephemeroptera in Hong Kong. Globally, the number of known genera is more than 30 and the total number of species is probably around 900.
Distribution: cosmopolitan and widely distributed.
Features for ID | Scientific name |
Double gills | |
Gills I - VI double Ventral gill lamellae rounded Hindwing pads absent |
|
--> Terga II & V with conspicuous dark markings medially |
Cloeon micki |
--> Terga yellowish brown with a pair of pale spots; unique reddish brown markings on segments II - III and V - VI |
Cloeon harveyi |
--> Terga yellowish brown with a pair of pale spots but without conspicuous reddish brown marking |
Cloeon nr. bengalense |
Ventral gill lamellae asymmetrical & pointed Hindwing pads present or reduced Lateral spines present on posterior abdominal segments |
|
--> Gills I - III with small dorsal flap, Gills IV - VII single |
Procloeon incanum |
--> Gills I - VI with dorsal flap, Gill VII single |
Procloeon venustum |
Single gills | |
Body dorso-ventrally flattened Femora with long dense setae dorsally Central filament greatly reduced to give a two-tailed impression |
|
--> Single dorsal tubercles on posterior margin of terga I - II, but two on terga III - IX |
Baetiella bispinosa |
--> Single dorsal tubercles on posterior margin of terga I - III, but two on terga IV - IX |
Baetiella trispinata |
--> No dorsal tubercles on abdomen |
Liebebiella vera |
--> No dorsal tubercles on abdomen |
Platybaetis bishopi |
--> No dorsal tubercles on abdomen |
Acentrella gnom (very rare) |
--> No dorsal tubercles on abdomen |
Undescribed sp. |
Femora with sparse stout setae dorsally 3 caudal filaments (central filament may be slightly shortened) |
|
--> Body dorso-ventrally flattened, no villiopore on femora, very long setae present on tibiae, pale coloration on tergum VIII |
|
----> Claw with two rows of denticles |
Chopralla fusina |
----> Claw without denticle |
Cloeodes longisetosus |
--> Body cylindrical & elongated, frontal ridge between antennae, no villiopore on femora, segment II of labial palp with a distinctive distolateral lobe, paraprocts without a prolongation |
|
----> 7 pairs of gills I - VII |
Labiobaetis atrebatinus orientalis (formerly L. morus) |
----> 6 pairs of gills II - VII |
Labiobaetis mustus |
----> 6 pairs of gills II - VII |
Labiobaetis diffundus |
--> Body cylindrical & elongated, frontal ridge between antennae, no villiopore on femora, no distolateral lobe on segment II of labial palp, paraprocts with a prolongation |
|
----> Gills II - VII |
Alainites acutulus |
----> Gills I - VII |
Alainites lingulatus |
--> Body dorso-ventrally flattened, no frontal ridge, dark markings on legs, villiopore present on fermora |
|
----> Gills II - VII |
Baetis maculosus |
----> Gills I - VII |
Baetis tatuensis |
----> Gills I - VII |
Baetis illiesi |
----> Gills I - VII |
Baetis qiweiae |
----> Gills I - VII |
Tenuibaetis peudofrequentus(formerly Baetiella peudofrequentus) |
--> Body cylindrical, no frontal ridge, no villiopore on femora |
|
----> Distinct markings |
Nigrobaetis facetus |
----> Abdomen plain without markings |
Nigrobaetis gracilentus |
Heptageniidae
It is the second largest family after Baetidae in Hong Kong. Globally, there are more than 20 genera in over 500 described species.
Distribution: mainly in the Holoarctic, Oriental, and Afrotropical regions.
Features for ID | Scientific name | |
Central filament greatly reduced to give a 2-tailed impression | ||
--> Distinctive sub-triangular shape of head, anterior end wider --> Gill I enlarged greatly to form disc-like structure beneath abdomen --> Posterior margin of terga I - IX with a pair of tubercules submedially |
Iron herklotsi | |
--> Not as above; head more generally obvate, gill I not enlarged greatly --> Two pale markings on head anterio-submarginally |
Epeorus sagittatus | |
Central filament not reduced, giving a 3-tailed impression | ||
--> Pronotum not expanded laterally as other heptageniids --> Gill I reduced, gills II - VII normal, oval shape --> No distinct markings on head or body |
||
|
Paegoniodes cupulatus | |
--> Pronotum expanded laterally, wider than mesonotum | ||
--> Pale spots present on anterior margin of head | ||
--> 6 distinct pale spots on anterior margin of head |
Electrogena ngi | |
--> 4 distinct pale spots on anterior margin of head |
Afronurus sinensis (formerly Cinygmina rubromaculata) | |
--> 4 diffuse pale smudges on anterior margin of head |
Compsoneuria taipokauensis | |
--> No pale spot on head --> Gills V & VI with a black apical process |
||
Afronurus dudgeoni (formerly Cinygmina dudgeoni) |
Leptophlebiidae
There are more than 640 described species in 130 genera.
Distribution: an extremely diverse cosmopolitan group.
Features for ID | Scientific name | |
Gill I single, gills II-VII slender & deeply forked | ||
--> Abdominal sterna reduced, gills arise ventrally | ||
Isca purpurea | ||
--> Gills borne laterally as usual | ||
--> Gills forked from the basal 1/3 of their length |
Paraleptophlebia rostrata | |
--> Gills forked from the basal 1/5 or 1/4 of their length |
Habrophlebiodes gilliesi | |
Gill I present or absent, Gills II-VII with plate-like lamellae | ||
--> Gills II-VII ovate with fringed margin | ||
Thraulus bishopi | ||
--> Gill I single slender, Gills II-VII double lamellae terminated with 3 long filaments | ||
--> Maxilla without distinct projection on inner corner | ||
--> median plate-like much larger & longer than lateral ones |
Choroterpes (Choroterpes) petersi | |
--> all 3 filaments subequal in length |
Choroterpes (Euthraulus) elliptica | |
--> all 3 filaments subequal in length |
Choroterpes (Euthraulus) trigonia (very rare) |
|
--> Maxilla with very long & distinct projection on inner corner | ||
--> Maxilla with very long & distinct projection on inner corner |
Choroterpes (Cryptopenella) facialis (very rare) |
Caenidae
Only a single genus (Caenis) in the subfamily Caenidae in Hong Kong.
Features for ID | Scientific name |
--> Anterolateral corner of mesonotum with a distinct process --> Dorsal surface of head, thoracic nota & forewing pads densely covered with rounded granules --> Operculate gills uniformly brown |
|
Caenis bicornis | |
--> Without any process at anterolateral corner of mesonotum | |
--> Dorsal surface of head, thoracic nota & forewing pads densely covered with rounded granules |
Caenis aspera |
--> Dorsal surface of head, thoracic nota & forewing pads densely covered with fine wrinkles and sparse tiny granules |
Caenis lubrica |
Ephemerellidae
Features for ID | Scientific name |
--> A robust appearance given by expanded mesonotum, enlarged femora, widened abdomen --> Gill III operculate, relatively large |
|
Torleya arenosa | |
--> Gills III - VII: III - VI similar in size, but VII smaller | |
Serratella albostriata |
Teloganodidae
Distribution: Afrotropical and Oriental regions. Only Teloganodes tristis is recorded in Hong Kong.
Features for ID | Scientific name |
--> Central filament greatly reduced to give a two-tailed impression (cf. 3-tailed in Ephemerellidae) --> Gills II - V (gill II largest) |
Teloganodes tristis |
Isonychiidae
Features for ID | Scientific name |
--> Coxal gill tufts present --> Conspicous double rows of long setae on inner side of femora & tibiae of forelegs --> Abdominal gills I-VII: large diffuse dark mark with small pale patch proximally |
Isonychia kiangsiensis |
References:
Tong, X. & Dudgeon, D. (2003) Two new species of Heptageniidae from China (Insecta, Ephemeroptera). Acta Zootaxonomia Sinica 28: 469-473.
Tong, X. & Dudgeon, D. (2002) Three new species of the genus Caenis (Ephemeroptera, Caenidae) from Hong Kong, China. Zoological Research 23: 232-238.
Tong, X. & Dudgeon, D. (2000) Ephemerellidae (Insecta: Ephemeroptera) from Hong Kong, China, with descriptions of two new species. Aquatic Insects 22: 197-207.
Dudgeon, D. (1996) Life histories, secondary production and microdistribution of heptageniid mayflies (Ephemeroptera) in a tropical forest stream. Journal of Zoology, London 240: 341-361.