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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Somatochlora Selys (Corduliidae) - Emeralds

Of the 26 species of Somatochlora found in North America, 12 species have been reliably recorded in Michigan. Sometimes commonly encountered corduliids, 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 (Walker 1908, 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, S. linearis, and S. tenebrosa are also known only from a few counties in the state, in the UP and LP, respectively. S. elongata, S. kennedyi, S. minor, S. walshi, and S. williamsoni are found in widely scattered localities in both the lower and upper peninsulas. S.forcipata, S. franklini, and S. incurvata have been found only in the UP. The early record for S. tenebrosa (Kormondy 1958), which did not have any locality information, has been determined to be S. hineana. S. hineana apparently favors 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 is known from several records in northern Ohio and central Indiana, and thus may also be encountered in the southern part of our state.

Key to adults (adapted from Needham et al. 2000)

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 nymphs (adapted from Daigle 1991, Cashett and Vogt 2001)

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

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
13
 
2a(1a) a. Middorsal hook apices always blunt Somatochlora williamsoni Walker
b. Hooks low and not falciform

2b
a. Middorsal hook apices always acute 3
b. Hooks usually erect and falciform, may be erect and straight or low and falciform
 
3a(2b) a. Middorsal hooks present on S3-9, middorsal hook length on S3 greater than 1/8 middorsal length of Ab3 4
3b a. Middorsal hooks present on Ab4-9, Ab5-9, or Ab6-9, if middorsal hook on Ab3, if present, then less than 1/8 middorsal length 5
 
4a(3a)

a. Palpal crenulations 4-5 each with group of 5-6 setae

Somatochlora minor Calvert
b. Palpal setae 6-8
c. Head width <6.0
4b a. Palpal crenulations 4-5 each with group of 8-12 setae Somatochlora hineana Williamson (in part)
b. Palpal setae 8-9
c. Head width >6.5
 
5a(3b) a. Ab9 with lateral spines at least 3/5 as wide as long 6
5b a. Ab9 with lateral spines less than 3/5 as wide as long 8
also: Middorsal hooks of Ab7-9 tergites with the posterior margin curved; epiproct not extending beyond cerci
 
6a(5a) a. Middorsal hooks on Ab7-8 with posterior margins straight Somatochlora hineana Williamson (in part)
also: Middorsal hooks on Ab3-9 or Ab4-9, hook well developed on Ab4
6b a. Middorsal hooks on Ab7-8 with posterior margins curved 7
 
7a(6b) a. Premental setae 12-15 Somatochlora linearis (Hagen)
b. Palpal crenulations 4-5 each with group of 7-8 setae
c. Vestigial middorsal hook sometimes on Ab3, small but well developed hook on Ab4
7b a. Premental setae 11-12 Somatochlora ensigera Martin
b. Crenulations 4-5 each with group of 5-7 setae
c. No middorsal hook on S3, middorsal hook on S4 small or vestigial
 
8a(5b) a. Palpal setae 8-9, rarely 10 10
b. Head width >6.4mm

8b
a. Palpal setae 6-7, rarely 8 11
b. Head width <6.4mm
 
9a(8a) a. Total length 20.0-22.0 Somatochlora tenebrosa (Say)
b. Palpal crenulations 4-5 each with group of 6-9 setae
c. Middorsal hooks on Ab4-9 or Ab5-9 d. Metatibia length-to-head width ratio >1.25
9b

a. Total length 23.5-25.0

Somatochlora hineana Williamson (in part)

b. Palpal crenulations 4-5 each with group of 8-12 setae
c. Middorsal hooks on Ab4-9 d. Metatibia length-to-head width ratio <1.25
 
11a(8b) a. Metafemur length 7.2-8.8mm Somatochlora elongata (Scudder)
b. Metatibia length 8.5-10.0mm
11b a. Metafemur length 6.0-7.0mm 12
b. Metatibia length 6.8-8.4mm
also: Middorsal hook on Ab9 extends to or beyond posterior margin of Ab10; in dorsal view (unextended specimens); epiproct not extending beyond cerci
 
12a(11b) a. Palpal setae 8 Somatochlora tenebrosa (Say)
b. Head width 6.2-6.4mm
c. Male epiproct with a pronounced anteapical swelling
12b a. Palpal setae rarely 8 Somatochlora walshii (Scudder)
b. Head width 5.5-6.0mm
c. Male epiproct without an anteapical swelling
also: Middorsal hook on Ab4 small, but well developed, >1/8 middorsal length of tergite; total length 21.0-22.5mm; metatibia length 7.4-8.4mm
 
13a(1b) a. Lateral spines distinct on Ab8-9 tergites Somatochlora cingulata (Selys)
also: Low, broad middorsal prominences on Ab4-9 in lateral view; metatibial length 8.5-9.1; lateral margins of male epiproct with prominent tubercles
13b a. Lateral spines absent on Ab8 tergite, or maybe present only on Ab9 tergite, which may be minute and only discernable in ventral view 14
 
14a(13b) a. Lateral spines absent on Ab9 Somatochlora forcipata (Scudder)
also: Posterior margins of Ab6-9 with two prominent dorsolateral tufts of long setae, Ab6 setae may be obscured by wing pads
14b a. Lateral spines present on Ab9, which may be minute, best observable from ventral view 15
 
15a(14b) a. Ab8 tergite with posterior margin having a distinct median tuft of long setae, best observed in dorsolateral view Somatochlora kennedyi Walker

15b
a. Ab8 without a median tuft of long setae, but distinct paired dorsolateral tufts may be present, best observed in dorsolateral view 16
 
16a(15b) a. Posterior margin of Ab8 and Ab9 with setal length relatively uniform Somatochlora franklini (Selys)
also: Head width < 5.9; total length 17-19; metafemur length usually < 5.8

16b
a. Posterior margin of Ab9 tergite, and usually Ab8, with setae forming two distinct rows of dorsolateral tufts, the setae between these tufts distinctly shorter 17
 
17a(16a) a. Dorsolateral tufts of setae on posterior margins of Ab6-9 distinct and widely separated by about the width of a tuft (Ab6 setae may be obscured by wing pads) Somatochlora forcipata (Scudder)
b. Head width less than or equal to 5.9mm
17b a. Dorsolateral tufts of setae on posterior margin of Ab9 and usually Ab8 distinct and widely separated by about the width of a tuft, and dorsolateral tufts less distinct and median gap narrowing progressively anteriad, with tufting of Ab6 absent or indistinct Somatochlora incurvata Walker
b. Head width >5.9mm
 

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

Species

length
setae
mental setae
no. of palpal crenations
max. no. of crenation setae
dorsal hooks
palpal
mental
outer
inner
0/+
Ab3
Ab4

cingulata

26-28
5-7
10-13
4-5 longest
3-4 variable
7-8
1-3
0
0
0

elongata

23-24.4
6-7
11-12
4-6 longest
6-8 shorter
9
5-6
+
0
+

forcipata

19-20
9-10
12-15
4-6 longest
4-5 shorter
7-9
3-5
0
0
0

franklini

17.5
7-8
13
4-6 longest
4-5 shorter
10
4
0
0
0

hineana

23-25
7-10
11-16
9-10 longest
3-5 shorter
9
12
+
v
+

kennedyi

21
9-10
12-13
4-6 longest
4-5 shorter
9-10
4
0
0
0

linearis

22
6-7
11-12
5-6 longest

9-10
5-7
+
0
v

minor

21-22.5
6-7
11-13
7-8 longest
5-6 shorter
9
5-6
+
+
+

tenebrosa

20-22
8
11-12
5-6 longest

9-10
6-7
+
0
0/v

walshi

20.5
7
9-10
7 longest
3 much shorter
9
4-5
+
0
v

williamsoni

23-25
8
11-12
4-5 longest

9-10
6-7
+
0
0

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.
Kormondy EJ. 1958. A catalogue of the Odonata of Michigan. Miscellaneous Publications, Museum of Zoology, University of Michigan, No. 104. 43pp.
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.
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.
Vogt, T. E. and E. D. Cashatt .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, E. B. 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: May 14, 2016 (EB)