Aquatic Insects of Michigan

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

Somatochlora Selys, 1871 (Corduliidae) - Striped Emeralds

Of the 26 species of Somatochlora found in North America, 12 species have been reliably recorded in Michigan, with an additional species occurring nearby and likely to be recorded.

Adults are dark with a metallic appearance, with reduced pale markings, brilliant green eyes, partly yellow face, and wings usually hyaline. Nymphs are medium-sized corduliids, moderately to very hairy. Sometimes commonly encountered, these large nymphs principally frequent streams but also are encountered in lakes as well as seeps and bogs, or springs and streams draining these systems. Classic historic works on the genus in our region (Walker 1907, 1918, Walker and Corbet 1975) are still valuable but have since been modified by subsequent taxonomic texts (see below).

Several species listed in the key below have only rarely been encountered in our state. S. cingulata (Selys, 1871), S. linearis (Hagen, 1861), and S. tenebrosa (Say, 1839) are also known only from a few counties in the state, in the UP and LP, respectively. S. elongata (Scudder, 1866), S. kennedyi (Walker, 1918), S. minor (Calvert, 1898), S. walshi (Scudder, 1866), and S. williamsoni Walker, 1907 are found in widely scattered localities in both the lower and upper peninsulas. S.forcipata (Scudder, 1866), S. franklini (Selys, 1878), and S. incurvata Walker, 1918 have been found only in the UP. The early record for S. tenebrosa (Say, 1839) (Kormondy 1958), which did not have any locality information, has been determined to be S. hineana Williamson, 1931. S. hineana apparently favors crayfish burrows of small seeps draining calcareous escarpments through thickly vegetated wetlands, and has been collected in both the eastern Upper and northern Lower Peninsulas (Vogt and Cashett 1994, Soluk et al. 1998, Steffens 1997, Steffens 1998). This species, which the USFWS currently lists as an endangered species, cannot legally be collected without permit. A verified record of S. tenebrosa has since been recorded from southern Michigan (O'Brien 2001). S. ensigera Martin, 1907 is known from several records in northern Ohio and central Indiana, and thus may also be encountered in the southern part of our state.

Taxonomic References: Cashett and Vogt 2001, Daigle 1991, Needham et al. 2014, Paulson 2011, Tennessen 2019, Walker 1918, Walker and Corbet 1975,

Key to adults

1a	Males	2
1b	Females	14
2a(1a) Males	a. Cerci each with a prominent, ventral, subapical tooth, longer than any other projection on cercus	3
2b	a. Cerci without any ventral, subapical spine or tooth	4
3a(2a)	a. Cerci in dorsal view markedly widened beyond midlength	Somatochlora linearis (Hagen)
	b. Cerci with very acute subapical, ventral tooth
	c. Thorax without laterla yellow markings
3b	a. Cerci in dorsal view not markedly widened beyond midlenth	Somatochlora ensigera Martin
	b. Cerci with subapical, ventral tooth blunt
	c. Thorax with large, well-defined lateral yellow markings
4a(2b)	a. Cerci with apices curved markedly upward, slender, acute or acuminate	5
4b	a. Cerci with apices not curved markedly upward, usually not especially slender, blunt to acute	9
5a(4a)	a. Cerci abruptly and strongly convergent in distal 1/4-1/2	Somatochlora cingulata (Selys)
	b. Metepimeron without a yellow spot or stripe
	c. Pterostimga 6x long as wide
	also: Epiproct roughly quadrangular, its apical margin broadly bifurcated and with a low median tooth; cerci each with a prominent, subbasal lateral tooth visible in dorsal view
5b	a. Cerci parallel or only gradually convergent in distal 1/4	6
	b. Metepimeron with a yellow spot or stripe
	c. Pterostigma 4-5x long as wide
6a(5a)	a. Abdomen, excluding caudal appendages, distinctly shorter than hindwing, widest at posterior end of Ab5	7
	b. Distal width of Ab5 about equal to its middorsal length
6b	a. Abdomen, excluding caudal appendages, about as long as hindwing, widest at posterior end of Ab6	8
	b. Distal width of Ab5 much less than its middorsal length
7a(6a)	a. Cerci each with a conspicuous apical tuft of setae, and without an inner, ventrobasal carina	Somatochlora walshii (Scudder)
	b. Mesepimeral yellow marking elongate
7b	a. Cerci each without a conspicuous apical tuft of setae, and with an inner, ventrobasal carina	Somatochlora minor Calvert
	b. Mesepimeral yellow marking rounded
8a(6b)	a. Cerci convergent to about midlength, approximately parallel beyond, and with a large ventrobasal tooth in addition to a smaller laterobasal one	Somatochlora elongata (Scudder)
	b. Mesepimeral and metepimeral pale stripes light yellow, conspicuous and well-defined
8b	a. Cerci parallel or very slightly convergent basally, more distinctly convergent in distal 1/4, and without a ventrobasal tooth	Somatochlora williamsoni Walker
	b. Mesepimeral and metepimeral pale stripes usually dull yellow, inconspicuous
9a(4b)	a. Cerci in lateral view each with a prominent dorsal tubercle at, or just beyond, the midlength, and bent sharply downward beyond the tubercle	10
	b. Metepimeral pale stripe not extending onto the thoracic venter
	c. Epiproct in lateral view curving strongly upward distally so that the apex is directed upward at a 45-90° angle
9b	a. Cerci in lateral view each without prominent dorsal tubercles, and not bent sharply downward in the apical 1/2	11
	b. If cerci somewhat angulated, then metepimeral spale strip extending onto the thoracic venter
	c. Epiproct in lateral view not curving strongly upward
10a(9a)	a. Apical 1/2 of each cercus more or less straight from the angulation at the dorsal tubercle to the tip	Somatochlora tenebrosa (Say)
	b. Epiproct curving upward at an angle of about 90°
	c. Mesepimeral and metepimeral stripes pale brownish yellow
10b	a. Apical 1/2 of each cercus with an additional sharp angulation at about 1/2 distance from the dorsal tubercle to the tip	Somatochlora hineana Williamson
	b. Epiproct curving upward at an angle distinctly less than 90°
	c. Mesepimeral and metepimeral stripes bright yellow
11a(9b)	a. Hindwing about 3/4x long as the abdomen, excluding caudal appendages, and with a dark brown basal spot extending beyond the anal triangle	Somatochlora franklini (Selys)
	b. Abdomen very slender, widest beyond Ab7
11b	a. Hindwing > 3/4x long as the abdomen, excluding caudal appendages, and without a dark brown basal spot	12
	b. Adomen not unusually slender, widest at Ab6 or Ab7
12a(11b)	a. Abdomen without lateral pale spots beyond Ab3	Somatochlora kennedyi Walker
	b. Metepimeral pale stripe indistinct or absent
	c. Cerci in dorsal view with a low lateral tubercle visible at about 3/5-2/3 length
12b	a. Abdomen with lateral pale spots at least on Ab5-7	13
	b. Metepimeral pale stripe present, usually distinct
	c. Cerci in dorsal view a lateral tubercle not visible
13a(12b)	a. Cerci hardly curved downward, in lateral view each without a prominent ventral tubercle at about 2/3 length	Somatochlora incurvata Walker
	b. Lateral thoracic pale markings dull and ill-defined
13b	a. Cerci markedly curved downward, in lateral view each with a prominent ventral tubercle at about 2/3 length	Somatochlora forcipata (Scudder)
	b. Lateral thoracic pale markings yellow, well-defined, ovate
14a(1b) (Females)	a. Subgenital plate, nearly perpendicular to the long axis of the abdomen, triangular and laterally compressed, at least as long as the lateral margin of Ab9	15
14b	a. Subgenital plate, approximately parallel or moderately inclined to the long axis of the abdomen, triangular, scoop-like or appressed to sternum, and usually not compressed or, if so, shorter than the lateral margin of Ab9	20
15a(14a)	a. Labrum largely yellow	16
	b. Postclypeus wholly yellow
15b	a. Labrum black	18
	b. Postclypeus black, at least centrally
16a(15a)	a. Thorax without lateral yellow markings	Somatochlora linearis (Hagen)
	b. Ab9, in lateral view, longer than high in natural position
16b	a. Thorax with lateral yellow markings	17
	b. Ab9, in lateral view, higher than long in natural position
17a(16a)	a. Subgenital plate distinctly longer than cerci	Somatochlora ensigera Martin
	b. Lateral yellow markings of thorax conspicuous and well-defined
17b	a. Subgenital plate shorter than cerci	Somatochlora tenebrosa (Say)
	b. Lateral yellow markings of thorax dull, often inconspicuous
18a(16b)	a. Abdomen, excluding cerci, <35mm long, as long as hindwings or slightly less	Somatochlora minor Calvert
	b. Mesepimeral and metepimeral pale markings ovate, well-defined
	c. Subgenital plate about as long as the cerci
18b	a. Abdomen, excluding cerci, >35mm long, slightly longer than hindwings	19
	b. At least mesepimeral pale marking elongate, sometimes dull and inconspicuous
	c. Subgenital plate shorter than cerci
19a(18b)	a. Yellow markings on thorax and base of abdomen clear, well-defined	Somatochlora elongata (Scudder)
	b. Abdomen without yellow spots posterior to Ab3
	c. In lateral view, subgenital plate bluntly pointed, not tapered apically, hardly compressed
19b	a. Yellow markings on thorax and base of abdomen dull, inconspicuous in mature specimens	Somatochlora williamsoni Walker
	b. Abdomen with yellow lateral spots on Ab5-7 or Ab5-8
	c. In lateral view, subgenital plate tapered to slender point, strongly compressed
20a(14b)	a. Subgenital plate distinctly shorter than sternum of Ab9, bilobed or truncate	Somatochlora cingulata (Selys)
	also: Subgenital plate <1/3x as long as sternum of Ab9; pale mesepimeral markings absent
20b	a. Subgenital plate nearly as long as sternum of Ab9, or longer, entire apically, scoop-shaped	21
21a(20b)	a. Labrum largely yellow	Somatochlora hineana Williamson
	b. Postclypeus almost wholly yellow
	also: Subgenital plate slightly longer than Ab10 sternum, projecting somewhat downward, triangular in profile; metepimerla pale stripe wider but distinctly shorter than mesepimeral stripe, not continuing downward onto thoracic venter
21b	a. Labrum black	22
	b. Postclypeus black, at least centrally
	c. Subgenital plate usually not distinctly longer than Ab9 sternum (except S. incurvata)
22a(21b)	a. Both mes- and metepimeral pale markings present, although sometimes obscure	23
	b. Ab5-7 or Ab5-8 with pale lateral spots
	c. Subgenital plate at least as long as Ab9 sternum
22b	a. Metepimeral pale markings absent	25
	b. Abdomen without pale lateral spots beyond Ab3
	c. Subgenital plate slightly shorter than Ab9 sternum
23a(22a)	a. Abdomen, excluding cerci, no longer than hindwing	Somatochlora walshii (Scudder)
	b. Subgenital plate largely black, its apex (in lateral view) curved ventrally
23b	a. Abdomen, excluding cerci, slightly longer than hindwing	24
	b. Subgenital plate yellowish, its apex (in lateral view) not curved ventrally
24a(23b)	a. Mesepimeral and metepimeral pale spots pale yellow, ovate, fairly well-defined	Somatochlora forcipata (Scudder)
	b. Subgenital plate about as long as Ab9 sternum
24b	a. Mesepimeral and metepimeral pale spots ochraceous, obscure or ill-defined	Somatochlora incurvata Walker
	b. Subgenital plate distinctly longer than Ab9 sternum
25a(22b)	a. With 6-9 cells between wing veins M1 and M1a	Somatochlora franklini (Selys)
	b. Hindwings each with a brown spot at base, extending beyond anal triangle, sometimes diffuse and extending along the costa or even over most of the wing
	c. Lateral surfaces of postclypeus black
	d. Cerci only slightly longer than subgenital plate
25b	a. With 11-20 cells between wing veins M1 and M1a	Somatochlora kennedyi Walker
	b. Hindwings yellowish at base but without a distnct spot
	c. Lateral surfaces of postclypeus brown
	d. Cerci near 2x as long as subgenital plate

Key to Mature Nymphs

1a	a. Middorsal hooks present at least on Ab6-9 tergites, usually erect, acute, and falciform, sometimes low and blunt but always visible in dorsal and lateral view on Ab6-9	2
	b. Setae on frontoclypeal ridge usually extending only to apex of Ant 1, sometimes to mid-length of Ant2
1b	a. Middorsal hooks absent on all tergites, or with low, broad middorsal prominences on S4-9 (cingulata) not erect or falciform, visible in lateral view but not dorsal view	10
	b. Setae on frontoclypeal ridge extending to apex of Ant2, sometimes beyond
2a(1a)	a. a. Ab9 posterolateral spine narrower, with basal width:length ratio <0.6	3
	b. Ratio of Ant2 length : Ant3 length usually >1.00
2b	a. Ab9 posterolateral spine stouter, with basal width:length ratio <0.6	7
	b. Ratio of Ant2 length : Ant3 length usually <1.00
3a(2a)	a. Ab5-5 middorsal hooks vestigial to extremely short, length 0.04-0.15	Somatochlora williamsoni Walker
	b. Ab7-9 middorsal hooks relatively short, those on Ab9 0.3 mm or less
3b	a. Ab5-5 middorsal hooks prominent, length 0.15-0.60	4
	b. Ab7-9 middorsal hooks relatively long, those on Ab9 0.4 mm or more
4a(3b)	a. Ab6-8 middorsal hooks with posteroventeral (lower) margin straight beyond extreme base (observe in lateral view)	Somatochlora ensigera Martin (in part)
	also: Ab6-9 middorsal hooks pointing posteriorly, dorsal setae of hooks as long as their hook width at base; 4 distinct setal clusters on dorsal rim of pterothorax; Ratio of cercus length : epiproct length for males 0.68-0.78, for females 0.62-0.69
4b	a. Ab6-8 middorsal hooks with posteroventral (lower) margin concave along entire margin (observe in lateral view)	5
5a(4b)	a. Long setae on posterior margin of compound eye 1.2 mm long or longer	Somatochlora elongata (Scudder)
	b. 3-4 setae on occiput and 6-15 setae on dorsum on mesothorax >2 mm
	c. Metathoracic femur length 6.90-7.90 mm
	d. Head width 5.95-6.40 mm
5b	a. Long setae on posterior margin of compound eye 0.6 mm long or less	6
	b. Setae on occiput and dorsum of mesothorax <1.0 mm
	c. Metathoracic femur length 6.15-7.10 mm
	d. Head width 5.60-6.05 mm
6a(5b)	a. Ab3 with distinct middorsal hook, 0.08-0.20 mm long	Somatochlora minor Calvert
	b. Ab4 middorsal hook length 0.24-0.51 mm (0.70-0.93x length of Ab5 middorsal hook)
	c. Ratio of metathoracic tibia length : head width 1.28-1.42
6b	a. Ab3 without middorsal hook	Somatochlora walshii (Scudder)
	b. Ab4 middorsal hook vestigial, length 0.00-0.12 (0.00-0.31x length of Ab5 middorsal hook)
	c. Ratio of metathoracic tibia length : head width 1.22-1.29
7a(2b)	a. Ab4 with vestigial middorsal hook, or only slightly raised area bearing a small cluster of setae	Somatochlora ensigera Martin (in part)
	b. Posteroventral margin of middorsal hooks of Ab6-9 straight, setae on dorsal margin as long as width of hook at mid-length
	c. Head width < 6.1 mm
7b	a. Ab4 with small but distinct middorsal hook, usually 0.05-0.27 mm (rarely vestigial)	8
	b. Posteroventral margin of middorsal hooks of Ab6-9 usually arched, sometimes slightly, setae on dorsal margin < width of hook at mid-length
	c. Head width usually > 6.1 mm
8a(7b)	a. Ab4 middorsal hook length < or = 0.5x that of Ab5	Somatochlora linearis (Hagen)
	b. Ab6-8 with 0-3 long piliform setae on posteror carina between the middorsal hook and lateral margin
	c. Ratio of metathoracic tibia length : head width >1.3
8b	a. Ab4 middorsal hook length = or > 0.5x that of Ab5	9
	b. Ab6-8 with 10-36 long piliform setae on posteror carina between the middorsal hook and lateral margin
	c. Ratio of metathoracic tibia length : head width usually <1.3
9a(8b)	a. Ab3 usually with a distinct or vestigial middorsal hook	Somatochlora hineana Williamson
	b. Ab4 middorsal hook length about 0.8x that of Ab5
	c. >30 moderately long (up to 0.8 mm) piliform setae on posterior carina of Ab6-8
	d. Metathoracic femur with 12-24 long stout setae on dorsal margin
9b	a. Ab3 usually without a vestigial middorsalhook	Somatochlora tenebrosa (Say)
	b. Ab4 middorsal hook length about 0.5x that of Ab5
	c. 10-20 moderately long (up to 0.7 mm) piliform setae on posterior carina of Ab6-8
	d. Metathoracic femur with <10 long stout setae on dorsal margin
10a(1b)	a. Prementum in ventral view covering most of the eyes when retracted	Somatochlora cingulata (Selys)
	b. Paraproct sharply acuminate, ratio of length : basal width in ventral view 1.80-2.05
	c. Dorsal rim of palpus with numerous short, stout, sharp setae in addition to medium and fine setae
10b	a. Prementum in ventral view covering less than half of eyes when retracted	11
	b. Paraproct acute, ratio of length : basal width in ventral view 1.25-1.75
	c. Dorsal rim of palpus with few, if any, short stout setae, usually only with medium and fine setae
11a(10b)	a. Metasternum with numerous slender, curved setae on anterior half, but with few or no setae >0.1 mm long on posterior half or middle of posterior margin	Somatochlora kennedyi Walker
11b	a. Metasternum with numerous slender, curved setae on entire surface, 0.1-0.3 mm long, including entire posterior margin	12
12a(11b)	a. Medial setae on posterior margin of Ab7-8 equal to or longer than sublateral setae	Somatochlora franklini (Selys)
	b. Dorsum of epiproct with a majority of setae = or >0.1 mm long and conspicuous
12b	a. Medial setae on posterior margin of Ab7-8 shorter than sublateral setae	13
	b. Dorsum of epiproct with a majority of setae < or = 0.05 mm long and inconspicuous
13a(12b)	a. Long, sublateral setae on posterior margin of Ab7-8 forming a distinct group on each side of the median, appearing tuft-like	Somatochlora forcipata (Scudder)
	b. Head width < 6.0 mm
	c. Male with cercus in dorsal view symmetrical, medial and lateral margins slightly convex
13b	a. Long, sublateral setae on posterior margin of Ab7-8 forming a loose,more continous group on each side of the median, not tuft-like	Somatochlora incurvata Walker
	b. Head width = or >6.0 mm
	c. Male cercus asymmetrical, medial margin straight, lateral margin convex

Character Table for Mature Somatochlora Nymphs of Michigan [under construction]

References

Cashatt ED, Vogt TE. 2001. Description of the larva of Somatochlora hineana with a key to the larvae of North American species of Somatochlora (Odonata: Corduliidae). International Journal of Odonatology 4(2):93-105.
Daigle JJ. 1991. A new key to the larvae of North American Somatochlora. Argia 3(3):9-10.
Hagen HA.1861. Synopsis of the Neuroptera of North America, with a list of the South American species. Smithsonian Miscellaneous Collections 4:1-347.
Harvey FL. 1898. A contribution to the Odonata of Maine, II. Entomological News 3:269-277.
Kormondy EJ. 1958. A catalogue of the Odonata of Michigan. Miscellaneous Publications, Museum of Zoology, University of Michigan, No. 104. 43pp.
Martin R. 1907. Cordulines. Collections zoologiques du Baron Edm.de Selys Longchamps, Catolgue systématique et descriptif. Coll. Selys Longchamps 17:1-94, f 1-99, cpl 1-3.
Needham JG, Westfall MJ, May ML. 2014. Dragonflies of North America. Third Edition.. Scientific Publishers: Gainesville, Florida. xvi + 657 pp.
O'Brien MF. 2001.Somatochlora tenebrosa at Ives Road Fen. Williamsonia 5(4): 7.
O'Brien MF. 2001. "Hine's emerald dragonfly: a federally-endangered species Somatochlora hineana Williamson. Williamsonia 5(2-3): 5.
Say, T. 1839. Descriptions of new North American neuropterous insects and observations on some already described by (the late) Th. Say. Journal of the Academy of Natural Science of Philadelphia 8:9-46.
Scudder SH. 1866. Notes on some Odonata from the White Mountains of New Hampshire. Proceedings of the Boston Society of Natural History 10:211-222.
Selys-Longschamps E. de. 1871. Synopsis des Cordulines. Bulletin de l'Académie royale des Sciences de Belgique (2)31:238-316; 519-565.
Selys-Longschamps E. de. 1878. Secondes additions au synopsis des Cordulines. Bulletin de l'Académie royale des Sciences de Belgique (2)45:183-222.
Smith WA. 1997. Wisconsin Williamsonia and T & E status for corduliids and gomphids. Williamsonia 1(4):7.
Soluk DA, Swisher BJ, Zercher DS, Miller JD, Hults AB. 1998. The ecology of Hine's emerald dragonfly (Somatochlora hineana): Monitoring populations and determining patterns of habitat use. Activity summary and report of findings (September 1996-August 1997). IL Nat. History Survey, Champaign, IL. 111 pp.
Steffens W. 1997. New Somatochlora county records and notes for the UP. Williamsonia 1(4):7.
Steffens WP. 1998. "New distribution records of Somatochlora hineana (Odonata: Corduliidae)." The Great Lakes Entomologist 31(1): 25.
Tennessen KJ. 2019. Dragonfly nymphs of North America: An Identification Guide. Springer International Publishing, Cham, Switzerland: xiv + 620 p.
Vogt TE., Cashatt ED. 1994. "Distribution, habitat, and field biology of Somatochlora hineana (Odonata: Corduliidae)." Annals of the Entomological Society of America 87(5): 599.
Walker EM. 1907. A new Somatochlora with a note on the species known from Ontario. The Canadian Entomologist 39:69-74.
Walker EM. 1918. On the American representatives of Somatochlora arctica with description of two new species (Odonata). The Canadian Entomologist 53:221-226.
Walker EM., Corbet JS. 1975. The Odonata of Canada and Alaska, Vol. 3. University of Toronto Press: Toronto. xvi + 308.
Williamson EB. 1931. A new North American Somatochlora (Odonata - Cordulinae). Occasional Papers of the Museum of Zoology, University of Michigan 225:1-8, 1 pl.

Page last edited: April 21, 2020 (EB)