Aquatic
Insects of Michigan
by
Ethan Bright, Museum of Zoology Insect Division and School of Natural
Resources and Environment
University of Michigan
Heptageniidae, Arthropleidae - Flat-headed Mayflies
Imagoes (Reproductive adults) (adapted from Edmunds and Waltz 1996, Edmunds et al. 1976)
1a a. Vein MA of hind wing simple, unforked (Figure 1)
Arthropleidae, Arthroplea bipunctata (McDunnough) b. Genital forceps of male with three short terminal segments also: Vein Rs of hind wing forming a regular fork 1b a. Vein MA of hind wing forked 2 b. Genital forceps of male with two short terminal segments Fig. 2
Fig. 32a a. Eyes large
Males, 3 b. Genital forceps present 2b a. Eyes smaller than male Females, 12 [note: Anepeorus females cannot be keyed] b. Genital forceps absent 3a(2a) a. Male fore tarsi 0.75x or less the length of the fore tibiae
Anepeorus simplex (Walsh) b. Male genitalia as in figure also: Nymphs from large rivers 3b a. Male fore tarsi longer than fore tibiae 4 b. Male genitalia not as above 4a(3b) a. Penes as in figure
Raptoheptagenia cruentata (Walsh) b. Longitudinal veins yellowish, crossveins dark also: Nymphs from large rivers 4b a. Penes not as above 5 b. Venation variable 5a(4b) a. Stigmatic area of fore wing with from 2 to many anastomoses of crossveins
Rhithrogena Eaton b. Basal segment of fore tarsi one-third or less the length of segment 2 c. Fore femora usually with a dark longitudinal streak near the middle 5b a. Stigmatic area of fore wing with or without anastomosed crossveins 6 b. If crossveins anastomosed, basal segment of fore tarsi 0.5x or more longer than segment 2 c. Fore femora usually without a dark longitudinal streak 6a(5b) Basal segment of fore tarsi equal or slightly longer than segment 2
Epeorus (Iron) Eaton also: Penes with well-developed median spines (titillators); stigmatic crossveins of fore wings not anastomosed 6b Basal segment of fore tarsi < 0.8x the length segment 2 7 also: Penes lobes fused medially at least in basal half; length of basal segment of fore tarsi < 0.66x (usually 0.5x) that of segment 2 7a(6b) Stenacron Jenson b. Basal crossveins between R1 and R2 dark margined 7b a. Wings may have crossveins below bullae clouded, but never as above 8 b. Crossveins between R1 and R2 rarely dark margined 8a(7b) a. Penes distinctly L-shaped, median titillators usually well-developed but without subdiscal sclerotized ridge 2
Stenonema Traver b. Basal segment of fore tarsi usually 0.33-0.66x length of segment 8b a. Penes not distinctly L-shaped as above, median titillators moderately to well-developed, with basal-lateral subdiscal sclerotized ridge 9 b. Basal segment of fore tarsi 0.2-0.5x length of segment 2 9a(8b) a. Eyes contiguous on vertex or separated by less than the diameter of the median ocellus
Nixe Flowers b. penes with minute dorsolateral spines, discal spines present or absent also: Basal costal veins weak 9b a. Eyes separated at least by the width of a lateral ocellus 10 b. Dorsolateral spines of penes present or absent 10a(9b) Eyes separated by little more than the diameter of a lateral ocellus
Heptagenia Walsh also: Penes with large dorsolateral spines, discal spines absent 10b Eyes separated at vertex by 3-5x the diameter of the median ocellus 11 11a(10b) a. Eyes separated at vertex by approximately the width of one compound eye
Leucrocuta Flowers b. Median titillators of male genitalia slender c. Penes with large dorolateral spines, discal spines present d. Crossveins behind costa and subcosta usually margined in brown 11b a. Eyes separated by width of 4-5x the width of the median ocellus Macdunnoa persimplex (McDunnough) b. Median titillators of male genitalia slender c. Penes with large dorsolateral spines, dical spines preseent d. Crossveins behind costa and subcosta often tan to black also: rare throughtout its range 12a(2b) Subanal plate with a moderate to deep V-shaped posteromedian emargination
Epeorus (Iron) Eaton also: Posterior margin of head only with a shallow emargination; basal costal crossveins of wing weakly developed, appearing detached anteriorly; stigmatic crossveins of wing not anastomosed; wing length < 12 mm 12b Subanal plate either broadly rounded or with only a slight posteromedian emargination 13 13a(12b) a. Stigmatic area of fore wing with two to many anastomosed crossveins
Rhithrogena Eaton b. Femora of most species with dark longitudinal streak near middle 13b a. Stigmatic area of fore wing usually without crossveins anastomosed 14 b. Femora usually without a dark longtiduinal streak near the middle 14a(13b) a. Wings with 2-3 crossveins below bullae between veins R1 and R2 connected or nearly connected by dark pigmentation, rarely only a dark spot Stenacron Jenson b. Basal crossveins between R1 and R2 dark margined 14b a. Wings may have crossveins below bullae clouded, but never as above Stenonema Traver, Heptagenia Walsh, Nixe Flowers, Leucrocuta Flowers, Macdunnoa persimplex (McDunnough) [no key available] b. Basal crossveins between R1 and R2 rarely margined
Mature nymphs (adapted from Edmunds and Waltz 1996, Edmunds et al. 1976)
1a a. All gills ventral
Raptoheptagenia cruentata (Walsh) b. Gill lamellae slender c. Gill filaments radiating out from a central plate also: From large rivers 1b a. Gills on at least Ab4-6 lateral 2 b. Gill lamellae usually broad c. Gill filaments variable 2a(1b) With only two well-developed caudal filaments, the terminal filament vestigial or absent
3 2b With three well-developed caudal filaments 4 3a a. Ab1-2 gills inserted ventrally, Ab3 gill inserted ventrally or ventrolaterally
Anepeorus simplex (Walsh) b. Tarsal claws with a single tooth and no denticles also: Mouthparts adapted for predation; head and each thoracic segment with paired dorsal tubercles; abdomen with single dorsal tubercles medially; from large rivers 3b a. Gills inserted laterally on Ab2-6, which may extend ventrally on Ab1 and Ab7 Epeorus (Iron) Eaton b.Tarsal claws without a tooth, but with three or more subapical denticles 4a(2b) Second segment of maxillary palpi longer than head is broad, in dorsal view conspicuous at the side or behind head
Arthropleidae, Arthroplea bipunctata (McDunnough) also: Pools, swamps and fens, small slow streams 4b Second segment of maxillary palpi not greatly enlarged, inconspicuous in dorsal view 5 5a(4b) Gills on Ab1 and Ab7 enlarged and meet (or almost meet) beneath the abdomen to form a ventral disk
Rhithrogena Eaton 5b Gills on Ab1 and Ab7 do not meet beneath the abdomen and usually are smaller than the intermediate pairs 6 6a(5b) Gill on Ab7 minute, no longer than the posterolateral projections of that segment also: rare throughtout its range
Macdunnoa persimplex (McDunnough) 6b Gills on Ab7 much larger than above 7 7a(6b) Gills on Ab7 reduced to slender filaments, their trachea absent or with few or no lateral branches
8 7b Gills on Ab7 similar to preceding pairs but smaller, trachea with lateral branches 9 also: Gill lamellae on Ab1 2/3x long as those on Ab2; fibrilliform portion of Ab1 gill usually subequal to, or shorter than, the lamella; labrum never more narrow at apex than at base 8a(7a) a. Gills on Ab1-6 with apex pointed
Stenacron Jenson b. Maxillae with stout spines on crown of galea-lacinia 8b a. Gills on Ab1-6 with apex rounded Stenonema femoratum (Say) b. Maxillae with setae or plumose hairs on crown of galea-lacinia 8c a. Gills on Ab1-6 with apex rounded or truncate Maccaffertium Bednarik b. Maxillae with setae or plumose hairs on crown of galea-lacinia 9a(7b) a. Ab7 gill with fibrilliform portion present and with numerous fibrils
Heptagenia Walsh b. Claws without denticles, but with one basal tooth 9b a. Ab7 gill without a fibrilliform portion 10 b. Claws with denticles 10a(9b) Head large, wider than pronotum, and with many dark spots near the anterior margin
Leucrocuta Flowers 10b Head not as wide as the pronotum, and without numerous spots near the anterior margin Nixe Flowers
References
Edmunds GF, Waltz RD. 1996. Ephemeroptera, pp. 126-163 in Merritt RW, Cummins KW (editors), An Introduction to the Aquatic Insects of North America, 3rd Edition. Kendall/Hunt Publishing Company: Dubuque, Iowa.
Edmunds GF, Jensen SL, Berner L. 1976. The mayflies of North and Central America. University of Minnesota Press: Minneapolis, Minnesota. x + 330 p.