Corduliidae - Emeralds

Adults (adapted from Needham et al. 2000)

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
	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

Nymphs (adapted from Walker and Corbet 1975, Needham et al. 2000)

1a	Middorsal hooks absent or reduced to low knobs	2
1b	Middorsal hooks present, well-developed on some abdominal segments	4
2a(1a)	a. Sides of thorax uniformly colored, without longitudinal stripe	Somatochlora (in part)
	b. Teeth on the distal margin of each labial palp usually deeply cut, sometimes obtusely angulate
2b	a. Sides of thorax with dark, broad longitudinal strip	3
	b. Teeth on the distal margin of each labial palp relatively low and rounded, at least on the ventromedial half of palpal margin
3a(2b)	a. Length of mature nymph >20 mm, usually about 23 mm	Cordulia shurtleffi Scudder
	b. Dorsal abdominal hooks absent, or if vestigial, highest on Ab8
	c. Lateral spines of Ab9 about 0.2x the length of that segments lateral margin (not including the spine)
3b	a. Length of mature nymph <20 mm, usually about 19 mm	Dorocordulia libera (Selys)
	b. Dorsal abdominal hooks stubby but distinct on Ab5-8 or Ab5-9, highest on Ab5
	c. Lateral spines of Ab9 about 0.4x the length of that segmentís lateral margin (not including the spine)
4a(1b)	Without lateral spines on Ab8	Williamsonia
	Habitat: Bogs or poor fens
4b	With lateral spines on Ab8	5
5a(4b)	Lateral spines on Ab9 about equal in length, and often much longer, than middorsal length of Ab9	Epitheca
5b	Lateral spines on Ab9 < 2.0x length of lateral spines on Ab8, and less than middorsal length of Ab9	5
5a(4b)	a. Crenations on distal margin of labial palpi nearly semicircular or even more deeply cut	Neurocordulia
	b. A pair of small tubercles on the epicranium
5b	a. Crenations on distal margin shallower than semicircle, incisions between teeth not as deep as distance between them	6
	b. Epicranium without tubercles
6a(5b)	Dorsal hooks on Ab6-9, those on Ab6 minute, length of those on Ab7-9 about equal to the middorsal length of its corresponding segment	Helocordulia uhleri (Selys)
6b	Dorsal hooks at least on Ab3-9 or 4-9, sometimes minute if on Ab3 or Ab4, often gradually increasing in length posteriorly to Ab7 or Ab8	Somatochlora (in part)

References

Needham JG, Westfall MJ, May ML. 2000. Dragonflies of North America. Scientific Publishers: Gainesville, Florida. xv + 940 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 reviewed: August 8, 2003 (EB)