Aquatic Insects of Michigan

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

Corduliidae (Emeralds) of Michigan - Identification

[under construction] References: Needham et al. 2010, Tennessen 2019, Walker & Corbet 1975)

Key to the Adults

1a	Veins M4 and Cu1 in fore wing diverging towards wing margin	2
1b	Veins M4 and Cu1 converging towards wing margin, often being parallel for most of the distance	3
2a(1a)	a. Small dragonflies (abdomen and hind wing each < 25 mm)	Williamsonia
	b. Top of head metallic green
	c. Triangles and subtriangles of fore wing and usually of hind wing of a single cell
	d. Hind wing without a basal spot
2b	a. Medium-sized dragonflies (abdomen and hind wing each > 30 mm)	Neurocordulia
	b. Without metallic lustre
	c. Fore wing triangle divided into 3 cells, hind wing divided into 2 cells
	d. Hind wing may have a basal amber spot
3a(1b)	a. Body brown, without metallic reflections	4
	b. Subgenital plate not projecting perpendicular to body axis
	c. Male mesotibiae with well-developed keels
	c. Male cerci blunt apically
3b	a. Body with strong green or blue-green metallic reflections, at least on thorax	5
	b. Subgenital plate projecting perpendicular to body axis
	c. Male mesotibiae with no or only vestigial keels
4a	a. Usually 2 crossveins immediately behind pterostigma	Helocordulia uhleri (Selys)
	b. Male abdomen widest at Ab8
	c. Length of subgenital plate no more than about 0.5x that of sternum of Ab9, divided for 2/3 length or less, each lobe not strap-like
4b	a. One crossvein immediately behind pterostigma	Epitheca
	b. Male abdomen widest at Ab6-7
	c. Length of subgenital plate equal or longer than sternum of Ab9, divided for nearly its entire length, each lobe strap-like
5a(3b)	a. Hindwings with 2 cubito-anal crossveins	Somatochlora
	b. Male mesotibiae entirely without keels
5b	a. Hindwings with 1 cubito-anal crossveins	6
	b. Male mesotibiae each with with at least a vestigial keel at apex
6a(5b)	a. Forewing triangle 2-celled	Cordulia shurtleffi Scudder
	b. 2 rows of cells in the trigonal interspace
	c. Male epiproct deeply bifurcated
6b	a. Forewing triangle 1-celled	Dorocordulia
	b. 1 row of cells in the trigonal interspace
	c. Male epiproct triangular

Key to the Nymphs

1a	a. Ab8 lateral sclerite (ventral view) without an anterolateral sclerite	2
	b. Ab2 with prominent middorsal hook
	c. Ab9 posterolateral spines long, usually extending beyond level of cerci tips
1b	a. Ab8 lateral sclerite (ventral view) without an anterolateral sclerite	3
	b. Ab2 without prominent middorsal hook
	c. Ab9 posterolateral spines variable, usually not extending to level of cerci tips
2a(1a)	a. Sides of thorax with distinctly delineated, brown longitudinal strip	Epitheca
	b. Ab6 sternite without an anterolateral sclerite
	c. Distal margin of palpus with 9-10 moderately produced crenations, relatively low and rounded, 3rd and 4th crenations H:W ratio usually <0.6
2b	a. Sides of thorax with distinctly delineated, brown longitudinal strip	Neurocordulia yamaskanensis (Provancher)
	b. Ab6 sternite with an anterolateral sclerite
	c. Distal margin of palpus with 7-8 highly produced crenations, 3rd and 4th crenations H:W ratio usually >0.7
3a(2b)	a. Palpus rugulose on most of the lateral surface	Williamsonia
	b. Frontoclypeal ridge produced, extending beyond apex of Ant1
	c. Ab8 with short setae, but without stout spinules on lateral margin
	d. Metathoracic femur of last instar nymph extending to tips of the metathoracic wing sheaths
3b	a. Palpus smooth on lateral surface, except for setal bases, sometimes with a slightly wrinkling in depression below the lateral margin of palpal dorsal rim	4
	b. Frontoclypeal ridge less produced, extending only to mid-length of Ant1
	c. Ab8 with long setae and/or stout spinules on lateral margin
	d. Metathoracic femur of last instar nymph extending well beyond tips of the metathoracic wing sheaths
4a(3b)	a. Side of thorax with a wide, complete, dark brown longitudinal stripe	5
	b. Ab7-9 tergites uniformly brown medially, rarely slightly paler than adjacent brown markings
4b	a. Side of thorax mostly uniformly colored or with obscure dark markings	6
	b. Ab7-9 tergites with pale blotches medially accentuated by darker sublateral markings
5a(4a)	a. Middorsal hooks absent	Cordulia shurtleffi Scudder
	b. Prementum width >5.0 mm
	c. Crenations on palpus with height : width ratio 0.43-0.46
5b	a. Ab6-7 with small middorsal hooks, sometimes also present on Ab5, Ab8-9	Dorocordulia libera (Selys)
	b. Prementum width <4.0 mm
	c. Crenations on palpus with height : width ratio 0.35-0.40
6a(4b)	a. Middorsal hooks present only on Ab6 or Ab7 to Ab8 or Ab9	Helocordulia uhleri (Selys)
	b. Rear margin of compound eye without a row of setae
	c. Dorsolateral rim of prementum without sharp, stout setae or fine pale setae
5b	a. Middorsal hooks either present on Ab3-, Ab4- or Ab5-9, or absent on all segments	Somatochlora
	b. Rear margin of compound eye with a row of short to long setae
	c. Dorsolateral rim of prementum variable setae, either conspicuous sharp, stout setae, or inconspicuous fine, pale setae

References

Needham JG, Westfall MJ, May ML. 2014. Dragonflies of North America. Third Edition.. Scientific Publishers: Gainesville, Florida. xvi + 657 pp.
Tennessen KJ. 2019. Dragonfly nymphs of North America: An Identification Guide. Springer International Publishing, Cham, Switzerland: xiv + 620 p.
Walker EM, Corbet JS. 1975. The Odonata of Canada and Alaska, Volume. 3. University of Toronto Press: Toronto, Ontario. xvi + 308 p.

Page created: July 27, 2003 (partially transferred from Odonata Larvae of Michigan, 1998)
Page last edited: April 26, 2020 (EB)