Aquatic Insects of Michigan

by Ethan Bright, Museum of Zoology Insect Division and School of Natural Resources and Environment
University of Michigan

Sialidae (Alderflies) of Michigan - Identification

The key below is derived from Ross and Frison (1937); subsequent updates will be incorporated in the near future.

Adults

1a Apex of abdomen without an ovipositor, but with a more or less complicated assemblage of parts - 2, males
1b Apex of abdomen with a broad, rounded ovipositor - 11, females

2a(1a) Sternite of Ab9 produced into a flap covering most of the genitalia; also: apex of lateral plates without a tooth; terminal plate narrowed at apex and not markedly incised - Sialis vagans Ross
2b Sternite of Ab9 not produced into a flap - 3

3a(2b) Terminal plate produced at apex into a pair of long arms - 4
3b Terminal plate sometimes with an apical incision, or a pair of short "horns," but not with a pair of long arms - 5

4a(3a) Apical arms of terminal plate separated at their base by a distance almost equal to their length - Sialis hasta Ross
4b Apical arms of terminal plate close together at base, and converging at tip - Sialis mohri Ross

5a(3b) Legs with femora rufous and tibiae the same color or blackish - 6
5b Legs black, or with tibiae slightly lighter than femora - 7

6a(5a) Head smooth and polished - Sialis glabella
6b Head punctured and dull - Sialis americana (Rambur)

7a(5b) Genital hooks long and whiplike, extending forward between the lateral plates - 8
7b. Genital hooks short, never longer than the plate from which they arise; lateral plates always closely appressed on meson; also: Apex of terminal plate not with hornlike or necklike processes; basal portion of of genital plates neither enlarged nor projecting over the terminal plate; Ab9 sternite with lateral setae fairly short 10

8a(7a) Apex of lateral plates produced into large knobs - Sialis infumata Newman
8b Apex of lateral plates not knoblike; also: Terminal plate short, its apex markedly cleft; genital hooks with a basal lobe - 9

9a(8b) Basal lobe of genital hooks relatively short, somewhat triangular, about <1.5x long as greatest width, as in figure (reversed in Ross 1937?) - Sialis velata Ross
9b Basal lobe of genital hooks long, markedly robust compared with distal lobe, basal end of lobe somewhat rectangulate, about 2x long as greatest width, as in figure - Sialis itasca Ross

10a(7b) Terminal plate with the apex narrow, tapered to a blunt point and not incised on meson - Sialis iola Ross
10b Terminal plate with apex wider, almost truncate; also: Terminal plate almost as wide as long, more or less pentagonal; genetial plates > 1/3 as long as terminal plate - Sialis joppa Ross

11a(2b) Sternite of Ab9 large, triangular and distinctly sclerotized - Sialis mohri Ross
11b Sternite of Ab9 apparently membranous and difficult to distinguish in uncleared specimens - 12

12a(11b) Legs with femora rufous and tibiae the same color or darker than femora - 13
12b Legs either entirely black or with the tibiae lighter than the femora - 14

13a(12a) Head smooth and polished - Sialis glabella
13b Head punctured and dull - Sialis americana (Rambur)

14a(12b) Ab8 sternite narrow and divided into two separate lobes by a median desion - Sialis aequalis Banks, Sialis vagans Ross
14b Ab8 sternite either wider, or not divided so completely into two separate parts - 15

15a(14b) Ab8 sternite as in figure, rectangular and with the distal portions set out as distinct swellings - Sialis infumata Newman
15b Ab8 sternite not as above, either with apex rounded out, or not set off with such conspicuous lobes - 16

16a(15b) Ab8 sternite flat, not tilted so that the apical margin is raised; bursa copulatrix with a terminal fingerlike process - Sialis velata Ross, Sialis itasca Ross
16b Ab8 sternite tilted so that the apical margin is markedly raised and the basal margin depressed; bursa copulatrix with terminus triangular - Sialis iola Ross, Sialis joppa Ross

Larvae (after Canterbury 1978)

1a Venter of abdomen with distinct crossbands, or solidly dark with pigment - 2
1b Venter of abdomen light in color, and lacking distinct cross bands, or with incomplete bands - 5

2a(1a) Background color of head and thorax dark with distinct lighter markings on head and pronotum - 3
2b Background color of head and thorax with faint markings on head and pronotum - 4

3a(2a) Labrum with a snout-like front; venter of abdomen with all but the last segment darkened completely, a narrow white line along the lateral edges - Sialis iola
3b Labrum without snout-like front as above; venter of abdomen with incomplete dark bands at edge of each segment - Sialis hasta

4a(2b) Pronotum with only a posterior pronotal medial spot visible, lateral elliptical spots large and ovoid on a dark background; labral marginal setae, usually 12 per side; meso- and metanotal patters as illustrated - Sialis joppa
4b Pronotum with pronotal medial spots faint; labral marginal setae usually 15 per side; meso- and metanotal patters as illustrated, with parts thickened and joined - Sialis aequalis

5a(1b) Mandible with a third tooth present; markings on head and thorax dark on a light background - Sialis glabella
5b Mandible without a distinct third tooth, represented only by a slight protuberance; head and thoracic figures light on a darker background - 6

6a(5b) Dorsum of abdomen with markings forming an anchor-like figure on each segment; pronotum with a rectangular light area at its center - Sialis vagans
6b Dorsum of abdomen with usual chevron markings; pronotum not as above - 7

7a(6b) Pronotum with small, dark elliptical pronotal spots, median portion light; venter of abdomen with cross bands incomplete at midline or absent - Sialis infumata Newman
7b Pronotum without dark elliptical pronotal spots, pattern may be indistinct; venter of abdomen usually white - 8

8a(7b) Head with darkened markings; pronotal medial spots dark; mesonotum and metanotum as in figure - Sialis itasca Ross
8b Head patterns faint; pronotal medial spots barely visible if at all; mesonotum and metanotum not as above - 9

9a(8b) Mesonotal figures with parts thickened and fused at median suture - Sialis velata Ross
9b Mesonotal figures with parts slim and not fused as above - Sialis mohri Ross