Aquatic Insects of Michigan
by Ethan Bright, Museum of Zoology Insect Division and School of Natural Resources and Environment
University of Michigan
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- Aquatic Insects of Michigan
Capniidae (Snowflies) of Michigan - Identification
Introduction
[under construction]
Adults (modified from Harper and Hynes 1971, Hitchcock 1974, and Ross and Ricker 1971)
| 1a | a. In dorsal view, epiproct behind Ab10 tergite | Males, 2 |
| b. Posterior margin of Ab8 sternum straight, not modified into a subgenital plate | ||
| 1b | a. Epiproct absent | Females, 14 |
| b. Posterior margin of Ab8 sternum posteriorly produced as a subgenital plate | ||
| 2a(1a) | Epiproct simple, comprising of only a single element | 3 |
| 2b | Epiproct consisting of two distinct elements, one dorsal, one ventral | 5 |
| 3a(2a) | a. R1 of forewing curved cepahlad just beyond the origin of the Rs | Capnia vernalis (Newport) |
| b. In ventral view, subanal plate (formed by the fusion of the two subanal lobes and the median fusion plate) pointed | ||
| 3b | a. R1 of forewing straight just beyond the origin of the Rs | Paracapnia, 4 |
| b. In ventral view, subanal plate trilobed | ||
| 4a(3b) | In lateral view, base of epiproct angulate in profile | Paracapnia angulata Hanson |
| 4b | In lateral view, base of epiproct evenly rounded in profile | Paracapnia opis (Newman) |
| 5a(2b) | a. R1 of forewing curved cepahlad just beyond the origin of the Rs | Capnura manitoba Claassen |
| b. Dorsal process on Ab7, absent on Ab8 | ||
| also: Epiproct with dorsal and ventral elements slender | ||
| 5b | a. R1 of forewing straight just beyond the origin of the Rs | 6 |
| b.Dorsal process on Ab8, or on both Ab7 and Ab8 | ||
| also: Anal lobe of hind wing nearly as large as rest of wing | ||
| 6a(5b) | Wings vestigial, represented only by minute scales | Allocapnia vivipara (Claassen) |
| also: In posterior view, dorsal process of Ab8 tergite with a low, sharp profile; in lateral view, apical segment of upper limb of epiproct only about half as long as the basal segment | ||
| 6b | Wings not vestigial, though may be shortened (brachypterous) | 7 |
| 7a(6b) | In lateral view, apical segment of upper limb of epiproct is long and flat to tip, very thin and regular in profile, and with short, dorsal retrorse spines | Allocapnia recta (Claassen) |
| also: Sclerous apex of process of Ab8 tergite appearing to be on on a high, narrowed elevated portion of tergite, its apical ridge semicircular | ||
| 7b | In lateral, apical segment of upper limb of epiproct is either short, narrow, or tip expanded | 8 |
| 8a(7b) | Dorsal process of Ab8 tergite forming a wide projection that is not mesally cleft | Allocapnia minima |
| also: In lateral view, epiproct with apical segment of upper limb extremely short, < 1/3x length of basal segment; dorsal process of Ab8 tergite high and angled posteriorly, its opaque tip minute | ||
| 8b | Dorsal process of Ab8 tergite mesally cleft, the resultant lobes either close together or far apart | 9 |
| 9a(8b) | Dorsal process of Ab8 tergite forming a pair of oblique rugose areas, their dorsal aspect U- or V-shaped | 10 |
| also: Setose process situated just below each lobe of the Ab8 tergal process | ||
| 9b | Dorsal process of Ab8 tergite forming a transverse bar or oval having 2-3 projecting apical points or lobes | 11 |
| 10a(9a) | a. Profile of dorsal process of Ab8 tergite fairly long and either declivitous or concave, its anterior corner angulate | Allocapnia frisoni Ross and Ricker |
| b. Dorsal aspect of dorsal process of Ab8 tergite somewhat U-shaped | ||
| also: Lateral aspect of rugose dorsal area of process of Ab8 tergite almost confluent with the outline of the dorsal margin of the segment | ||
| 10b | a. Profile of dorsal process of Ab8 tergite either much shorter or not declivitous | Allocapnia granulata (Claassen) |
| b. Dorsal aspect of dorsal process of Ab8 tergite with the posterior margin angulate or rounded | ||
| also: Epiproct with length of apical and basal segments of the upper limb about equal | ||
| 11a(9b) | In lateral view, Ab7 tergite with a sclerotized dorsal process nearly as large as the process on Ab8 tergite, the later situated near the posterior margin of the segment, sloping and declivitous | Allocapnia illinoensis Frison |
| also: Dorsal process on Ab8 tergite with two lateral points; epiproct with membranous apex of upper limb merging impreceptibly with the more sclerous basal portion, its dorsal aspect somewhat bulbous | ||
| 11b | Ab7 tergite with either no process or with only a small process that is merely a slightly elevated ridge | 12 |
| 12a(11b) | In posterior view, dorsal process of Ab8 tergite with a mesal point at least half the height of a lateral lobe | Allocapnia nivicola (Fitch) |
| also: In lateral view, profile of dorsal process of Ab8 tergite about as high as wide, and without a posterodorsal projecting corner; epiproct with lower limb wide and extending laterally considerably beyond the upper limb, the lateral margins often angulate | ||
| 12b | In posterior view, dorsal process of Ab8 tergite without a mesal point, only with two apical (lateral in posterior view) lobes | 13 |
| 13a(12b) | In lateral view, epiproct with its apical segment of upper limb ovoid in profile, and less than one-half length of its base | Allocapnia rickeri Frison |
| also: In posterior view, Ab8 tergite with dorsal process forming two large, widely separated lobes, divided on meson to basic circumference of the segment | ||
| 13b | In lateral view, epiproct with its apical segment of upper limb slenderer in profile, and more than one-half the length of its base | Allocapnia pygmaea (Burmeister) |
| also: In posterior view, Ab8 tergite with dorsal process forming two large, separated lobes, in lateral view process remote from the anterior sclerous band of the segment; In lateral view, Ab8 dorsal process high, its anterior face steep, its posterior profile usually shouldered | ||
| 14a(1b) | a. Anal lobe of hindwing exceptionally large, nearly as large as rest of wing, with vannus extending considerably beyond the cord | Allocapnia, 15 |
| b. R1 of forewing straight just beyond its origin | ||
| 14b | a. Anal lobe of hindwing much smaller, of normal size | Paracapnia angulata Hanson and Paracapnia opis (Newman) |
| b. R1 of forewing straight just beyond its origin | ||
| also: 0-3 costal crossveins in forewing | ||
| 14c | a. Anal lobe of hind wing much smaller, of normal size | 24 |
| b. R1 of forewing curved cephalad justy beyond the origin of R1 | ||
| 15a(1b) | In ventral view, Ab8 tergite having little or no mesal membranous area, the sclerous portion bridging the entire segment for half or more of its length | Allocapnia vivipara (Claassen) |
| also: Ab7 and Ab8 sternites fused, the mesal portion of the fusion forming a solid longitudinal area in which the intersegmental suture is obliterated | ||
| 15b | In ventral view, Ab8 tergite having a fairly wide mesal membranous area extending its whole length | 16 |
| 16a(15b) | Ab7 and Ab8 sterna solidly fused on the meson, the line of fusion indicated by a dark line or crease | 17 |
| 16b | Ab7 and Ab8 sterna either completely separated by a membranous area, or joined on the meson by only a faint semisclerous strap | 20 |
| 17a(16a) | Line of fusion between Ab7 and Ab8 sternites not evident on meson, the two sclerites joinging without a break in profile | Allocapnia rickeri Frison |
| also: Ab8 sternite much shortern than that of Ab7, with its profile evenly rounded; apex of Ab8 sternite straight; body length of well-extended specimen < 7 mm | ||
| 17b | Line of fusion between Ab7 and Ab8 sternites indicated by a dark line, and a break in the profile | 18 |
| 18a(17b) | Apex of Ab8 sternite with a wide but shallow sagittate mesal portion contrasting sharply with the much less sclerous remainder of the mesal area of the sclerite | Allocapnia illinoensis Frison (in part) |
| 18b | Mesal area of apex of Ab8 sternite not contrasting noticeably with the more basal portion of the sclerite, its apex round or truncate | 19 |
| 19a(18b) | In ventral profile, Ab8 sternite produced into a broad rounded flap capable of being reflexed under the edge of the sternite, projecting markedly beyond the mesal edge of the lateral humps, which are chiefly membranous | Allocapnia pygmaea (Burmeister) |
| 19b | In ventral profile, Ab8 sternite with the apical flap relatively narrow and truncate, capable of folding dorsally under the edge of the sternite, and when extended reaching considerably beyond the extensively sclerotized lateral humps | Allocapnia nivicola (Fitch) |
| 20b | Central portion of Ab8 sternite forming a flat, sclerous area extending full length of the sternite, and truncate or nearly so at the apex, narrower than the lateral humps | Allocapnia minima (Newport) |
| 20b | Central portion of Ab8 sternite with the flat area either wedge-shaped, constricted in the middle, only partially sclerous, or only indistinctly differentiated from the lateral areas except at the apex of the segment | 21 |
| 21a(20b) | In ventral view, basomesal portion of Ab8 sternite forming either a narrow or pale strap joing the seventh abdominal sternite, the fusion line being only fainted sclerous | Allocapnia illinoensis Frison (in part) |
| also: Mesal portion of Ab8 sternite with only a sagittate apical area dark, the remainder of which being much lighter | ||
| 21b | In ventral view, Ab7 and Ab8 sternites completely separated by membrane, in contracted specimens the membrane cannot be seen without manipulation | 22 |
| 22a(21b) | In ventral view, apicomesal portion of Ab8 sternite not markedly differentiated from the lateral areas, its apical margin usually concave, without a projecting, short mesal point or acuate lobe | Allocapnia recta (Claassen) |
| 22b | In ventral view, apicomesal portion of Ab8 sternite differentiated into a sagittate or emarginate, fluted area set off laterally by pale membranous areas | 23 |
| 23a(22b) | Apicomesal process of Ab8 sternite wider, its margin usually truncate or emarginate | Allocapnia frisoni Ross and Ricker |
| 23b | Apicomesal process of Ab8 sternite narrower, usually pointed like a spearhead | Allocapnia granulata (Claassen) |
| 24a(14c) | a. Median sclerotized area of Ab8 subgenital plate narrow, not more darkly sclerotized than remainder of plate, with the sclerotized connection between Ab7-8 sternites wide | Capnura manitoba Claassen |
| b. Subgenital tract not visible through Ab8 sternite | ||
| 24b | a. Median sclerotized area of Ab8 subgenital plate wide, its lip darkened, and with the sclerotized bridge bewteen Ab7-8 sternites narrow | Capnia vernalis (Newport) |
| b. Subgenital tract visible through Ab8 sternite | ||
Mature nymphs (adapted from Harper and Hynes 1971, Stewart and Stark 2000)
| 1a | 1-3 short dorsal and/or ventral intercalary setae on some cercal segments | 2 |
| 1b | Cercal segments without short or long intercalary segments | 3 |
| 2a | a. Body and appendages densely clothed with long, stout bristles | Paracapnia Hanson, 4 |
| b. Some abdominal bristles > 0.5x as long as their segments | ||
| also: Cercal segments with at most 1 short dorsal and 2 ventral intercalary setae not forming a prominent vertical fringe | ||
| 2b | a. Body and appendage bristles few or short | Capnura manitoba Claassen |
| b. Abdominal hairs or bristles < 0.3x as long as their segment | ||
| also: Mesosternal furcasternum 0.4-0.5x the intercoxal width; right ventral mandibular tooth with 6-8 small basal teeth | ||
| 3a | a. Inner margin of hind wingpads unnotched, or notched close to the tip, or hind wingpads sometimes much reduced | Allocapnia Claassen, 5 |
| b. Right ventral mandibular tooth with deep basal serrations | ||
| c. Tip of galea expanded, with a fringe of long hairs | ||
| 3b | a. Inner margin of hind wingpad notched, sometimes weakly, at about midlength | Capnia vernalis (Newport) |
| b. Right ventral mandibular tooth without deep basal serrations | ||
| c. Tip of galea evenly tapered or pointed | ||
| also: Lacinia with < 15 ventral teeth of uneven length; femur and tibia with < 20 intercalary surface hairs, and usually with no long dorsal femoral fringe hairs | ||
| 4a(2a) | a. Middle and distal segments of cerci with along intermediate bristle the ventral base of the segment | Paracapnia angulata Hanson |
| b. Bristles on the inner surface of the tibiae short, half as long as the width of the respective tibiae | ||
| 4b | a. Cercal segments without intermediate bristles | Paracapnia opis (Newman) |
| b. Bristles on the inner surface of the tibiae long, as long as the width of the respective tibia | ||
| note: A. frisoni not keyed | ||
| 5a(3a) | Abdominal tergites clothed with erect hairs throughout | Allocapnia illinoensis Frison |
| 5b | Erect hairs not evenly distributed, but more abundant near the posterior margin and sometimes at midlength of the tergites | 6 |
| 6a(5b) | In lateral view, abdominal tergites bearing, in addition to the prostrate clothing hairs, only a terminal row of erect hairs | 7 |
| 6b | In lateral view, abdominal tergites bearing, in addition to the prostrate clothing hairs, terminal and intermediate rows of erect hairs | 10 |
| 7a(6a) | Galea of maxilla narrowly pointed, with a well-developed fringe of hairs | Allocapnia minima (Newport) |
| also: Length small, body length up to 5.5 mm (not including cerci) | ||
| 7b | Galea of maxilla gradually tapered, tip rounded | 8 |
| 8a(7b) | Galea with a wide fringe of setae on the outer surface | Allocapnia pygmaea (Burmeister) |
| also: Longest hairs in fringe of galea shorter than the width of the galea at the point of insertion; clothing hairs numerous; supraanal lobe of mature male nymph long | ||
| 8b | Galea with a narrower fringe, usually < 10 hairs | 9 |
| 9a(8b) | a. Terminal abdominal tergites with intermediate erect hairs only on the lateral margins | Allocapnia nivicola (Fitch) |
| b. Suprranal lobe of mature male nymph long | ||
| 9b | a. Terminal abdominal tergites with intermediate erect hairs on lateral thirds of the tergites, and because none occur on the middle third of the segment, in lateral view none are seen | Allocapnia recta (Claassen) |
| b. Suprranal lobe of mature male nymph short | ||
| 10a(6b) | a. Erect bristles on margin of abdominal tergites long, about 1/2x long as the mid-dorsal length of respective tergite | Allocapnia rickeri Frison |
| b. Intermediate bristles few | ||
| c. Body length moderate, about 6-8 mm (not including cerci) | ||
| 10b | a. Erect bristles on margin of abdominal tergites short, about 1/3x as long as the mid-dorsal length of respective tergite | 11 |
| b. Intermediate bristles numerous | ||
| c. Body length longer, about 8-10 mm (not including cerci) | ||
| 11a(10b) | a. In lateral view, head and pronotum hairy | Allocapnia vivipara (Claassen) |
| b. Mature male nymph without wing pads | ||
| c. Supraanal lobe of mature male nymph 2x as long as Ab10 as seen in lateral view | ||
| 11b | a. In lateral view, head and pronotum with fewer hairs | Allocapnia granulata (Claassen) |
| b. Mature male nymph with short wing pads | ||
| c. Supraanal lobe of mature nymph short, about equal in length as Ab10 as seen in lateral view | ||
References
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Harper PP, Hynes HBN. 1971. The Capniidae of Eastern Canada (Insecta; Plecoptera). Canadian Journal of Zoology 49:921-940.
Hitchcock SW. 1974. Guide to the Insects of Connecticut. Part VII. The Plecoptera or stoneflies of Connecticut. State Geological and Natural History Survey of Connecticut Bulletin 107:1-262.
Ross HH, Ricker WE. 1971. The classification, evolution, and dispersal of the Winter Stonefly Genus Allocapnia. Illinois Biological Monographs 45:1-166.
Stewart KW, Stark BP. 2002. Nymphs of North American stonefly genera. Second Edition. The Caddis Press: Columbus, Ohio. xii + 510 p.
Page created: December 14, 2003; Last edited: November 06, 2013 (EB)