Aquatic
Insects of Michigan
by
Ethan Bright, Museum of Zoology Insect Division and School of Natural
Resources and Environment
University of Michigan
Capniidae - Snowflies
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
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 (EB)
Page last reviewed: December
15, 2003 (EB)