Aquatic Insects of Michigan

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

Argia (Coenagrionidae) (Dancers) of Michigan - Identification

A very speciose New World genus of coenagrionid damselflies, most species are found in Central and South America, and many more species there remain to be described. Five species have been recorded in Michigan (see below). A. apicalis, A. sedula and A. tibialis are known only from the Lower Peninsula; the other two species - A. fumipennins violacea and A. moesta - are widespread throughout the state.

These robust, short and stocky nymphs (Fig. 1) are distinguished from our other coenagrionids by large, flattened prementum that lack premental setae and have three pointed hooks (one movable hook and two pointed palpal lobes). Unlike most other coenagrionids in Michigan, Argia are principally lotic, inhabiting slow-moving sections of streams and rivers, but our species are also found in lentic habitats. A. moesta has been found along rock-margined lake sections and under rocks of stream rapids (Walker 1953), and A. apicalis, A. sedula and A. tibialis along lake shores, ponds, ditches or swamps (Westfall and May 1996). Adults tend to be medium to large-sized damselflies. Their common name pertains to the characteristic irregular manner of flight, described by Paulson (2011) as "a bouncy or jerky movement through the air quite different from the smooth forward motion of bluets, fortails, and other pond damsels and more jewelwing flight. They are much more likely to land flat on rocks, logs, or soil than other types of pond damsels, and they stay in the open, not moving slowly through vegetation as do many other pond damsels." Walker (1953) notes that they prefer alighting on bare sunny spots, and are alert, being more difficult to capture.

Taxonomic References: Paulson (2011), Walker (1953) and Westfall and May (2006)

Key to Adults

1a	a. Ventral portion of Ab2-3 modified as secondary genitalia	Males, 2
	b. Terminal end of Ab10 with a pair of flanking claspers (caudal appendages)
1b	a. Ab2 venter morphologically undifferentiated from adjoining segments	Females, 6
	b. Distal portion of Ab8 sternum with a genital aperature, with a well-developed ovipositor underneath Ab9 and beyond
2a(1a)	a. Paraprocts with apexes nearly entire and broadly rounded, with small superior prominence but no distinct inferior lobe	Argia moesta (Hagen)
	b. Cerci as long as paraprocts or nearly so, with small ventrolateral excavation just before the apex that fits over superior prominence of the paraprocts
	c. Mesepimeron with a wide, black central stripe in additon to the humeral stripe, or largely black
	d. Pterostigma surmounting more than one cells
2b	a. Paraprocts usually with distinct inferior as well as superior lobe, thus appearing bifid or trifid in lateral view	3
	b. If paraprocts nearly entire at apex, then markedly longer than the cerci
	c. Mesepimeron not as above, although often with the humeral stripe forked
	d. Pterostigma surmounting one cell or less
3a(2b)	a. Total dark area of Ab3-6 and thoracic dorsum greater than the pale area of the same parts	Argia sedula (Hagen)
	also: Inferior lobe of paraprocts larger than superior lobe, with distinct marginal denticles; Ab3-4 with pale areas confined to basal bands
3b	a. Total dark area of Ab3-6 or thoracic dorsum less than the pale area of the same parts	4
4a(3b)	a. Ab3-6 largely pale dorsally (purplish), generally with a black apical or subapical band which may become wider in the more caudal segments	Argia fumipennis violacae (Hagen)
4b	a. Ab3-6 largely black dorsally, with only a pale basal band and at most a very fine pale line dorsally	5
5a(4b)	a. In posteroventral view, cerci trifid	Argia apicalis (Say)
	b. Humeral stripe much narrower than the antehumeral, generally amere hairline throughout most of its length
	c. Ab8 dorsum blue
5b	a. In dorsal or posteroventral view, cerci bifid	Argia tibialis (Rambur)
	b. Humeral stripe wider, generally about eual in width to the antehumeral
	c. Ab8 dorsum black
6a(1b)	a. Mesostigmal plates each with a small lobe just lateral to the mesepisternal pit, and with a distinct dorsal posterior ridge medial to each lobe	Argia moesta (Hagen)
	b. Abdomen usually >32 mm
	c. Middorsal thoracic stripe usually <0.1 width of thoracic dorsum
	d. No promiment mesepisternal tubercle
	e. Pterostigma surmounting more than 1 cell
6b	a. Mesostigmal plates otherwise	7
	b. Abdomen usually <32 mm, or if longer, then either the middorsal thoracic stripe is 0.25x or more the width of the thoracic dorsum, or there is a prominent mesepisternal tubercle
	c. Pterostigma usually surmounting 1 cell or less
7a(6b)	a. Posterior lobe of mesostigmal plate forming a flange-like ridge, extending at least 0.75x width of the plate, which increases in height medially and is turned so the entire ventral surface is clearly visible in strict lateral view	Argia sedula (Hagen)
	b. Abdomen usually lacking well-defined dark markings
7b	a. Posterior lobe of mesostigmal plate, if present, variously formed but very rarely with the ventral surface visible in strict lateral view, except at extreme medial end	8
	b. Abdomen with well-defined dark areas
8a(7b)	a. Dorsum of Ab3-6 almostly entirely black, the pale areas restricted to a basal transverse band and/or a dorsal hairline or spindle-shaped mark	9
	b. Wings not very dark
8b	a. Dorsum of Ab3-6 usually with considerably more extensive pale areas, often mostly pale	11
	b. Wings usually very dark brown
9a(8a)	a. Middrosal thoracic stipe not more than 0.1x width of the thoracic dorsum	Argia apicalis (Say), in part
9b	a. Middorsal thoracic stripe wider, at least 0.25x width of the thoracic dorsum	10
10a(9b)	a. Ab3-7 with distal expansion of black dorsal stripe distinct and well-defined laterally	Argia tibialis (Rambur)
	b. Pale dorsal strip of Ab9 often not extending to the base of the seghment, sometimes merely an apical spot
	c. Arms of middrosal thoracic carina anterior to its bifurcation forming an angle of 90° or more
10b	a. Ab3-7 with distal expansion of black dorsal stripe absent, ill-defined, divided laterally, or containing a pale lateral spot	Argia apicalis (Say), in part
	b. Pale dorsal stripe of Ab9 always extending to the base of segment, although occasionally only as a hariline
	c. Arms of middorsal thoracic carina anterior to its bifurcation forming an angle considerably < 90°
11a(8b)	a. Middorsal thoracic stripe <0.33x width of thoracic dorsum, often little more than a hairline	Argia apicalis (Say), in part
11b	a. Middrosal thoracic stripe 0.33x or more the width of thoracic dorsum	Argia fumipennis violacae (Hagen)

Mature Nymphs

1a	a. Lateral gills with a marginal fringe of stout setae (in addition to any fine setae) for at least 3/4 their length on both the ventral and dorsal margins	2
1b	a. Lateral gills with a marginal fringe of stout setae extending at most about 2/3 the length of the ventral margin only, much less on the dorsal margin	3
2a(1a)	a. Ant1-2 pale	Argia sedula (Hagen)
	b. Dark bands of femora narrower than the intervening pale space
2b	a. Ant2 at least partly or wholly dark	Argia fumipennis violacae (Hagen)
	b. Dark bands on femora wider than the pale intervening spaces, sometimes hardly visible
3a(1b)	a. Lateral carina of lateral gills with setae, if any, restricted to the basal 1/4 of the gill	Argia moesta (Hagen)
	b. Palpal setae 0-1, sometimes with up to 3 tiny supernumerary setae
3b	a. Lateral carina of lateral gills with setae extending at least 1/3 the length of gills	4
	b. Palpal setae 1-4
4a(3b)	a. Palpal setae 2-4	Argia apicalis (Say)
	b. Lateral gills usually widest at about the mid-point, about 2/5 as wide as long
	c. Dark bands of femora usually wider than the intervening spaces
4b	a. Palpal setae usually 1	Argia tibialis (Rambur)
	b. Lateral gills usually widest distinctly beyond the mid-point, and narrower, about 1/3 as wide as long
	c. Dark bands of femora usually narrower than the intervening pale spaces

References

Paulson D. 2011. Dragonflies and damselflies of the East. Princeton Field Guides. Princeton University Press, Pinceton, New Jersey, USA. 538 p.
Walker EM. 1953. The Odonata of Canada and Alaska, Volume One, Part I: General, Part II: The Zygoptera - Damselflies. University of Toronto Press, Toronto, Ontario. 292 pp.
Westfall MJ, May ML. 2006. Damselflies of North America, Revised Edition. Scientific Publishers, Gainesville, Florida, USA. xii + 502 pp.

Page created: 11 August 1998 - Last updated: May 19, 2020 (EB)