Aquatic Insects of Michigan

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

Baetiscidae (Baetisca) of Michigan - Identification

Introduction

under construction

Imagoes (adapted from Pescador and Berner 1981)

1a	Males (Fig. 1)	2
1b	Females (end of abdomen not as in Fig. 1)	4
2a	Penes lanceolate, apically blunt (Fig. 2)	Baetisca obesa (Say)
2b	Penes deltoid, apically pointed (Fig. 3)	3
Fig. 1Fig. 2 Fig. 3
3a(2b)	Longitudinal veins of fore wing brown	Baetisca laurentina McDunnough
3b	Longitudinal veins of fore wing pale, vein C, Sc, and R pale to light brown	Baetisca lacustris McDunnough
4a(1b)	a. Body length approximately 6.5-8.5 mm	Baetisca lacustris McDunnough
	b. Fore wing length 9.0-10.5 mm
	c. Caudal filaments 5.0 mm, white to light brown
	d. Abdominal terga white to grayish-brown, chalky-white on Ab7-10 terga
	e. Legs light tan with few brown spots on the femora, tibiae with basal brown markings which almost completely encircle the metatarsus
4b	a. Body length 8.3-12.3 mm	Baetisca laurentina McDunnough
	b. Fore wing length 8.8-15.6 mm
	c. Caudal filaments 5.0-8.3 mm, brown
	d. Abdominal terga light brown
	e. Legs brown, femora slightly darker than other leg segments
4c	a. Body 7.0-9.0 mm	Baetisca obesa (Say)
	b. Forewing 9.0-12.0 mm
	c. Caudal filaments 5.5-7.0 mm, pale with brown annulations at articulations
	d. Abdominal terga purplish-brown, darkest on Ab2-6, Ab7-10 tergites with submedial and posterolateral whites areas
	e. Legs light brown washed with darker brown, most noticeable on femora

Mature nymphs

1a	Dorsal projections on mesonotal shield weakly to moderately developed, their height less than, or subequal to, that of the medial hump	Baetisca lacustris McDunnough
	also: Mesonotal shield distinctly longer than wide, and with a middorsal depression; lateral spines of the mesonotal shield > 1.5x as long as their basal width; thoracic and abdominal sterna freckled with brown spots; prominent brown spot on the thoracic sternum medial to each coxa (Fig. 4); posteromedian elevation on Ab7-9 tergites weakly developed
1b	Dorsal projections on mesonotal shield well-developed, distinctly taller than medial hump	2
Fig. 4
2a(1b)	a. Frontal projection well-developed, distinctly extended beyond the anterior margin of the head (Fig. 5)	Baetisca obesa (Say)
	b. Ventral margins of the mesonotal shield lack a dark-brown outline
	c. Ab2-6 sternites with prominent dark-brown spots near the lateral margin
2b	a. Frontal projection developed, but not extended beyond the anterior margin of the head (Fig. 6)	Baetisca laurentina McDunnough
	b. Ventral margins of the mesonotal shield prominently outlined with dark brown
	c. Ab2-6 sternites lacking prominent dark-brown sublateral spots, but freckled with brown
Fig. 5 Fig. 6

Species Descriptions

The following species descriptions are taken from Pescador and Berner (1981).

Baetisca lacustris McDunnough

Male imago (in alcohol). Body: Body length 6.9-9.0 mm; fore wing 9.0-10.5 mm; caudal filaments 5.0-8.0 mm. Head: Brown; antennae brown; eyes continguous dorsally. Thorax: Nota pale grayish to brown; scutellum brown with margins darker; sterna pale to light brown. Wings: Longitudinal veins of fore and hind wings usually colorless, sometimes with light brownish tint in C, Sc, and R1 of fore wing; membrane hyaline. Legs: Tan, washed with grayish-brown in some specimens; fore tarsi narrowly annulate with brown at each joint; meso- and metatarsi with a trace of a narrow, dark ring at each joint; claws pale to brownish. Abdomen: Terga white to grayish-brown, chalky-white laterally on tergites 7-10 in most individuals; sterna pale; genital forceps pale to brownish; penes deltoid, apically pointed, base gradually enlarged; caudal filaments white to light brown.
Female imago (in alcohol). Body: Body length 6.5-8.5 mm; fore wing 9.0-10.5; caudal filaments 5.0 mm. Other than sexually dimorphic traits, description of male same for female.
Mature nymph (in alcohol). Body: Body length 6.8-10.2 mm; caudal filaments 2.1-3.0 mm. Head: Tan with pronounced brown freckling [note: may be reduced]; small occipital tubercles; frontal projection small, anterior and posterior areas slightly depressed; genal shelf prominent and rounded at outer angle; antennae pale. Thorax: Mesonotal shield relatively broad, ratio of length-to-width 1.4:1.0; lateral spines of notal shield long, approximately 1.8x as long as basal width, sharply pointed [note: rarely may be rounded at tip, or long and pointed, or relatively short]; dorsal projections weakly developed, distinctly lower than medial hump; mesonotal shield tan, overlaid with extensive brown mottling; sterna tan with large brown spots; conspicuous brown spots between the pro- and mesocoxae and the meso- and metacoxae [note: rarely absent, or large and elongate]. Legs: Light tan with a few brown spots on the femora; tibiae with basal brown markings [may be lacking, or reduced to only one spot], almost completely encircle the metatarsus. Abdomen: Ab7-9 tergites and posterior 1/2 of Ab6 tergite with scattered brown spots; brown, median, longitudinal line on the anterior 1/2 of Ab7-9 tergites, barely evident on Ab10 tergite [variation: may be obsolescent or may extend the full length of the tergite]; sterna tan with scattered brown spots, becoming less numerous posteriorly; posterolateral projections and posteromedian elevations on Ab7-9 tergites weakly developed; caudal filaments pale.

Baetisca laurentina McDunnough

Male imago (in alcohol). Body: Body length 8.8-10.8 mm; fore wing 10.7-12.8 mm; caudal filaments 8.0-10.0 mm. Head: Brown; antennae light brown; eyes almost continguous dorsally. Thorax: mesonotum dark brown; scutellum ranging from dark brown to almost black; sterna light brown. Wings: Longitudinal veins of fore and hind wings brown, crossveins colorless; membrane hyaline with a brownish tint at the extreme base; stigmatic area of fore wing opaque, bullae prominent. Legs: Yellowish to light brown; brown at articulations of the meso- and metathoracic legs. Abdomen: Terga light brown to brown; sterna paler, whitish on Ab7-9 sternites in some specimens; genital forceps brown; penes deltoid, apically pointed, base gradually enlarged; caudal filaments brownish, darker at articulations.
Female imago (in alcohol). Body: Body length 8.3-12.3 mm; fore wing 8.8-15.6; caudal filaments 5.0-8.3 mm. Head: Grayish-brown, rarely whitish; antennae light brown. Thorax: As in male above, except generally paler. Wings: As in male above. Legs: Yellowish, except tarsi tinted with grayish-brown; tarsal articulations brown, claws brown. Abdomen: Terga light brown; sterna paler.
Mature nymph (in alcohol). Body: Body length 8.3-9.7 mm; caudal filaments 2.2-2.8 mm. Head: Dorsum mottled with brown; posterior margin dark brown; frontal projection developed, bifid with each part depressed dorsally and divergent, extended forward to at least the level of the anterior margin of the head; prominent ridge anterior to the frontal projection; genae slightly produced outwards and angulate; antennae yellowish, the distal segments brown. Thorax: Mesonotal shield relatively long and narrow, length-to-width ratio 1.6:1.0; anterolateral and lateromedial lobes weakly developed; lateral spines relatively short, about as long as basal width, rounded at the tips; dorsal projections prominent and divergent, highter than the medial hump; anteromedial hump absent; mesonotal shield mottled with brown, ventral margin strongly outlined with dark brown; sterna mottled with brown. Legs: Brown, femora slightly darker than other leg segments. Abdomen: Ab7-9 tergites extensively mottled with brown laterally; tergal pigmentation most intense on the posterior portion of Ab6, least on Ab10 tergite with the base of the segment dark brown; median brown line on Ab7-9 tergites; sterna with scattered brown mottling; posterolateral projections of Ab6-9 weakly developed, largest on Ab9 but not extended beyond the posterior extension of the subanal plate; posteromedian elevations on Ab7-9 tergites weakly developed; caudal filaments brown.

Baetisca obesa (Say)

Male imago (in alcohol). Body: Body length 6.0-8.0 mm; fore wing 8.0-10.0 mm; caudal filaments 6.0-7.5 mm. Head: Dark brown; antennae brown; eyes continguous dorsally. Thorax: Brown; mesonotum with dark mottling; scutellum dark purplish-brown; metanotum dark brown; prosternum purplish-brown, mesonotum glistening brown, metasternum gray. Wings: Longitudinal veins of fore and hind wings colorless except C, Sc, and R1 of fore wing which are brownish basally [note: rarely vein pigmentation may extend to the stigma, area basal to humeral brace may be dark brown, occasionally light pigmentation on all main veins]; membrane hyaline; stigmatic area opaque. Legs: Tan; tarsal segments narrowly annulate with brown, claws brownish; femora lightly washed with brown. Abdomen: Terga heavily mottled with brown, strongest concentration of spots on Ab1-2 terga; sterna paler than terga, mottled with brown laterally; Ab7-9 sternites rather pale medially; genital forceps pales, penes yellowish, lancelate, apically blunt and gradually enlarged basally, caudal filaments pale with brown annulations at articulations, vestigial median filament dark brown.
Female imago (in alcohol). Body: Body length 7.0-9.0 mm; fore wing 9.0-12.0 mm; caudal filaments 5.5-7.0 mm. Head: Pale brown, mottled with purplish-brown; antennae purplish-brown. Thorax: Mesonotum brown with a wide darker brown median strip; scutellum dark brown; sterna light brown. Wings: As in male above. Legs: Light brown washed with darker brown, most noticeable on femora; markings of tarsal segments as in male above. Abdomen: Terga purplish-brown, darkest on Ab2-6 terga, Ab7-10 terga with submedial and posterolateral white areas; sterna pale with dark-brown, lateral lines running the slength of the segment; similar horizontal lines on the intersegmental membranes except at middle of abdomen [note: most females have broad, lateral , longitudinal dark-brown markings on abdominal sternites, and transverse dark-brown lines on the intersegmental membranes, but some female individuals may have these obscured]; caudal filaments as in male above.
Mature nymph (in alcohol). Body: Body length 7.6-10.2 mm; caudal filaments 2.3-2.6 mm. Head: Covered in brown mottling; frontal projection bifid, long, extended well beyond the anterior margin of the head, excavated dorsally; genal shelf small, rounded at the anterolateral edge; male nymphs with vestiges of a pair of occipital tubercles between the compound eyes, more pronounced in female nymphs [note: occasionally obsolete]; antennae yellowish. Thorax: Mesonotal shield relatively long and narrow, length-to-width ratio 1.7:1.0; lateral spines relatively short, may be straight or slightly recurved posteriorly; dorsal spines well-developed and distinctly higher than the medial hump; mesonotal shield tan, mottled with dark brown continuing to the ventral edge; sterna pale medially, heavily mottled with dark brown laterally. Legs: Femora heavily mottled with brown, pale at extreme distal margin; tibiae pale with median, borwn band; tarsi with brown median band; claws pale, tip orange brown. Abdomen: Ab6-9 tergites with a broad lateral longitudinal dark-brown band, middle pale; anteromedian brown dash on Ab7-8 terga; sterna heavily mottled with brown, less concentrated medially; Ab9 sternite with brown coloration concentrated laterally; Ab2-6 sterna each with a prominent dark-brown spot near the lateral margins; posterolateral projections on Ab7-9 moderately developed; posteromedian elevation on Ab7-9 tergites weakly developed; basal 1/3 of caudal filaments brownish, remainder pale.

References

Hilsenhoff WL. 1984. Identification and distribution of Baetisca nymphs (Ephemeroptera: Baetiscidae) in Wisconsin. The Great Lakes Entomologist 17(2):51-52.
Pescador ML, Berner L. 1981. The mayfly family Baetiscidae (Ephemeroptera). Part II. Biosystematics of the genus Baetisca. Transactions of the American Entomological Society 107(3):163-228.

Page created: November 13, 2003; Last edited: November 06, 2013(EB)