Aquatic Insects of Michigan

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

Coenagrion of Michigan

Chiefly a Palaearctic genus, two of three species known from North America reach our area. These moderate-sized damselflies - especially nymphs - closely resemble Enallagma and Ischnura, and diagnostic keys for nymphs (e.g., Walker 1953, Westfall and May 2006) include these species with Enallagma. Despite their resemblance, molecular and morphological evidence suggests a phylogenetic relationship that is more separate than previously supposed (Brown et al. 2000, May 2002, O'Grady and May 2003). A commonly used diagnostic character to differentiate Enallagma from Coenagrion and Ischnura - 6 vs.7 antennal segments - is not reliable (Westfall and May (2006), pers. obs.).

Coenagrion are widely distributed in northern latitudes, and is probably univoltine in Michigan.Walker (1953, p. 179) notes that C. resolutum, which is widely distributed in Michigan, inhabits a wide variety of lentic habitats, including "almost any small permanent or subpermanent body of still water...ordinary ponds and prairie sloughs with marshy borders; in springy cat-tail marshes; in dark calla ponds; in sphagnum pools, in cool northern spruce or tamarack swamps, and in the marginal vegetation of slow weedy streams." C. interrogatum is known only from the Upper Peninsula of Michigan (MOS record database, search October 2007). This species inhabits cold swamps and open bogs, partial to areas of open bog or marsh (Walker 1953, p. 181-183).

Taxonomic references (Westfall and May 2006)

Adults

1a	Males	2
1b	Females	3
2a(1a)	a. Pale antehumeral stripes narrower than the black humeral stripes and, when divided, resembling an exclamation mark, the long anterior part tapering to a point posteriorly	Coenagrion resolutum (Hagen)
	b. Venter of metathorax without drak markings
2b	a. Pale antehumeral stripes wider (in the middle) than the black humeral stripes, nearly always divided, the long anterior part not tapering posteriorly	Coenagrion interrogatum (Hagen)
	b. Venter of the metathorax heavily marked with black, the pattern including a median Y-shaped figure
3a(1b)	a. Venter of thorax wholly pale	Coenagrion resolutum (Hagen)
	b. Metapleural suture with black spot confined to the fossa
	c. Ab3-7 without ventrolateral dark streaks, and with only small dorsolateral, basal pale areas
	d. Ab8-9 dorsally almost wholly black
3b	a. Venter of thorax heavily marked with black	Coenagrion interrogatum (Hagen)
	b. Metapleural suture marked with black anterior to the fossa
	c. Ab3-7 with long ventrolateral dark streaks, and with wider pale basal annuli
	d. Ab8-9 each with an extensive posterodorsal blue area

Nymphs

1a	a. Median gill < 5x as long as wide, and usually slightly acuminate apically	Coenagrion resolutum (Hagen)
	b. Cerci of male without a dorsomedial concavity
	c. Ovipositor rudiments of female extending more than 0.6 mm beyond posterior row of denticles on Ab9 sternum
	d. Metafemur usually > 2.9 mm
1b	a. Median gill 5x or more long as wide, and usually not acuminate apically	Coenagrion interrogatum (Hagen)
	b. Cerci of male with distinct dorsomedial concavity
	c. Ovipositor rudiments of female extending < 6.0 mm beyond posterior row of denticles on Ab9 sternum
	d. Metafemur usually < 2.9 mm

References

Brown JM, McPeek MA, May ML. 2000. A phylogenetic perspective on habitat shifts and idversity in the North American Enallagma damselflies. Systematic Biology 49:697-712.
May ML. 2002. Phylogeny and taxonomy of the damselfly genus Enallagma and related taxa (Odonata: Zygoptera: Coenagrionidae). Systematic Entomology 27:387-408.
O'Grady EW, May ML. 2003. A phylogenetic reassesment of the subfamilies of Coangrionidae (Odonata: Zygoptera). Journal of Natural History 37:2807-2835.
Walker EM. 1953. The Odonata of Canada and Alaska, Volume 1. University of Toronto Press, Toronto, Ontario, Canada. xi + 292 pp.
Westfall MJ, May ML. 2006. Damselflies of North America, Revised Edition. Scientific Publishers, Gainesville, Florida, USA. xii + 502 p.

Page last edited: Sunday, May 15, 2016 (EB)