Aquatic Insects of Michigan

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

Aeshna (Aeshnidae) (Mosaic Darners) of Michigan - Identification

Aeshna is the most speciose Holarctic genus of Aeshnidae, and 11 species occur in Michigan. As adults are strong fliers, most of our species are widely distributed and recorded from both the LP and UP. Four species are northernly in distribution: A. eremita and A. sitchensis have been recorded only in the UP and the as far south as Mecosta Co. in the LP, A. subarctica only in the UP, and A. juncea, a holarctic species, recorded only from Isle Royale in Lake Superior and Whitefish Point in Chippewa Co. Rhionaeschna mutata, formerly grouped in Aeshna, was separated from the genus by von Ellenreider (2003), and is a member of a primarily Neotropical group which also includes R. multicolor (Hagen) in the western US. R. mutata has been found only in the southern part of the LP.

The adult has hues of blue and yellow sometimes fade in preserved specimens unless treated with acetone (Needham et al. 2014). These are beautiful bluish brown darners that are the dominate aeshnid of our region. Strong fliers, they are sometimes encountered far from water from where their immature stages develop. Nymphs usually are found clinging to vegetation in lakes and ponds and sometimes in slower sections of streams and rivers. As their clinging habits often make them conspicuous, larger specimens are often subject to fish predation. However, the tables may be turned, with larval and small juvenile fish being included in the diet of larger individuals together with other aquatic invertebrate organisms.

With some rather subjective determinations of diagnostic features, some earlier keys for aeshnid immatures (e.g., Needham and Westfall 1955) are not reliable for many species. Walker's (1958) outstanding treatment of the Canadian species works well for Michigan, although some of his metrics were not consistent (DuBois & Tennessen 2015). Tennessen's recent (2019) tome is highly recommended, though species-level determination for immatures often requires precise microscopic measurement.

(Taxonomic References: Paulson 2011, Needham et al. 2014, Tennessen 2019, Walker 1908, Walker 1912, Walker 1958)

Adults

1a	a. Males	2
1b	a. Females	12
2a(1a)	a. Anal triangle of hindwing 3- or 4-celled	3
	b. Spines of anterior lamina vestigial
	c. Cerci more or less paddle-shaped, withour dorsal carina
2b	a. Anal triangle of hindwing 3- or 4-celled	4
	b. Spines of anterior lamina vestigial
	c. Cerci more or less paddle-shaped, withour dorsal carina
3a(2a)	a. Ab4-6 with paired, ventral pale spots	Aeshna umbrosa Walker
	b. Rear of head predominantly yellow or light brown
3b	a. Ab4-6 without paired, ventral pale spots	Aeshna constricta Say
	b. Rear of head black
	also: Mesepimeral pale stripes with margins strongly sinuate; mesepisternal pale stripes broad posterodorsally, tapering anteroventrally; anal loop usually with 2 cells in anterior row; frontoclypeal suture without a dark line
4a(2b)	a. Eyes in contact middorsally for distance little greater than the length of the occiput	Aeshna sitchensis Hagen
	b. Mesepimeral and metepimeral pale stripes <1mm wide, and extremely sigmoid, bent twice at almost right angles
	also: Ab2-7 mostly dark dorsally; postfrons with a transverse basal stripe produced slightly forward on each side of T-spot; cerci in dorsal view with acute apices
4b	a. Eyes in contact middorsally for distance almost 2x, or more, the length of the occiput	5
	b. Mesepimeral and metepimeral pale stripes wider, or if not, than not sigmoid
5a(4b)	a. Anteromedial process of each anterior hamule long	6
	b. Spines of anterior lamina long and slender
5b	a. Anteromedial process of each anterior hamule short	7
	b. Spines of anterior lamina short and stout
6a(5a)	a. Mes- and metepimeral pale stripes broad and straight, both lacking posterior projection from the upper end	Aeshna juncea (Linnaeus)
	b. Anteromedial processes of the anterior hamules with acute and somewhat hooked apices
	c. Spines of the anterior lamina curved ventrally
6b	a. Mes- and metepimeral pale stripes constricted near midlength, the mesepimeral stripe with a narrow posterior projection from the upper end	Aeshna subarctica Walker
	b. Anteromedial processes of the anterior hamules with rounded apices
	c. Spines of the anterior lamina straight and slender
7a(5b)	a. Cerci each with a distinct ventrobasal tubercle	Aeshna tuberculifera Walker
	b. Dorsum of Ab10 black
	c. Anterior margin of mesepimeral pale stripe nearly straight
7b	a. Cerci each without ventrobasal tubercles	8
	b. Dorsum of Ab10 with pale spots
	c. Anterior margin of mesepimeral pale stripe excavated or sinuate
8a(7b)	a. Mesepimeral pale stripe sickle-shaped, curving anteriorly at the top	Aeshna clepsydra Say
	b. 2 very large pale spots on the metepisternum between the mes- and metepimeral pale stripes
8b	a. Mesepimeral pale stripe not sickle-shaped	9
	b. Spots on the metepisternum small or absent
9a(8b)	a. Mesepisternal pale stripes absent, or represented by small, ill-defined, elongate spots	Aeshna interrupta Walker
	b. Mes- and metepimeral pale stripes either narrow and nearly straight, or divided into upper and lower spots
9b	a. Mesepisternal pale stripes complete, expanded at the posterodorsal ends	10
	b. Mes- and metepimeral pale stripes not divided (mesepimeral stripe may be strongly constricted), relatively wide for at least part of their length and with the anterior margins more or less sinuate or excavated
10a(9b)	a. Frontoclypeal suture with a black band	Aeshna eremita Scudder
	b. Cerci, in lateral view, rounded apically, without a terminal spine and not decurved, the dorsal carina strongly elevated distally and with 6-8 well-developed denticles
10b	a. Frontoclypeal suture without a black band	11
	b. Cerci, in lateral view, acute apically, with a terminal spine and usually distinctly decurved, the dorsal carina only slightly elevated distally and with 0-6 well-developed denticles
11a(10b)	a. Anteromedial process of each anterior hamule directly anteriorly, subparallel, with only the apices convergent	Aeshna canadensis Walker
	b. Anterior margin of the mesepimeral pale stripe abruptly constricted to form an almost right-angled notch
11b	a. Anteromedial process of each anterior hamule directly ventromedially, convergent throughout their length	Aeshna verticalis Hagen
	b. Anterior margin of the mesepimeral pale stripe constricted less abruptly to form an obtusely-angled notch
12a(1b)	a. Eyes in contact middorsally for distance little greater than the length of the occiput	Aeshna sitchensis Hagen
	b. Mesepimeral and metepimeral pale stripes <1mm wide, and extremely sigmoid, bent twice at almost right angles
10b	a. Eyes in contact middorsally for distance almost 2x, or more, the length of the occiput	11
	b. Mesepimeral and metepimeral pale stripes wider, or if not, than not sigmoid
13a(11b)	a. Styli of ovipositor at least as long as Ab10 tergum	14
	b. Cerci widest at or basal to midlength, their lateral margins convex in bsal 1/5-1/4
13b	a. Styli of ovipositor distinctly shorter than Ab10 tergum	15
	b. Cerci widest distal to midlength, their lateral margins nearly straight in basal 1/5-1/4
14a(13a)	a. Anterior margin of mesepimeral pale stripe sinuate	Aeshna constricta Say
	b. Posterodorsal end of metepimeral pale stripe extended ventrally along the posterior edge of the metepimeron
	c. Ab3 with the lateral carinae absent or vestigial
14b	a. Anterior margin of mesepimeral pale stripe not sinuate	Aeshna tuberculifera Walker
	b. Posterodorsal end of metepimeral pale stripe not extended ventrally along the posterior edge of the metepimeron
	c. Ab3 with the lateral carinae well-developed
15a(13b)	a. Basal plate of ovipositor, in ventral view, with posterior edge distinctly bilobed	16
	b. Lateral genital plates absent
15b	a. Basal plate of ovipositor, in ventral view, with posterior edge straight or slightly rounded	17
	b. Lateral genital plates present
16a(15a)	a. Mes- and metepimeral pale stripes broad and straight, both lacking posterior projection from the upper end	Aeshna juncea (Linnaeus)
	b. Anteromedial processes of the anterior hamules with acute and somewhat hooked apices
	c. Spines of the anterior lamina curved ventrally
16b	a. Mes- and metepimeral pale stripes constricted near midlength, the mesepimeral stripe with a narrow posterior projection from the upper end	Aeshna subarctica Walker
	b. Anteromedial processes of the anterior hamules with rounded apices
	c. Spines of the anterior lamina straight and slender
17a(15b)	a. Anterior margin of mesepimeral pale stripe not sinuate, stripe not divided and generally at least 1 mm wide	Aeshna umbrosa Walker
	b. Mesepisternal pale stripes well-developed
	c. Genital valves of ovipositor each without a minute tuft of setae at, or just before, the posteroventral angle
	also: Ab4-6 with paired, ventral, pale spots; rear of head predominantly yellow or light brown
17b	a. Anterior margin of mesepimeral pale stripe strongly sinuate, or stripe strongly constricted or divided into an upper and lower spot	18
	b. If neither of above are true, then mesepimeral pale stripe less than 1 mm and mesepisternal pale absent or represented by small, ill-defined, elongate spots
	c. Genital valves of ovipositor each with a minute tuft of setae at, or just before, the posteroventral angle
18a(17b)	a. Mesepimeral pale stripe sickle-shaped, curving anteriorly at the top	Aeshna clepsydra Say
	b. 2 very large pale spots on the metepisternum between the mes- and metepimeral pale stripes
18b	a. Mesepimeral pale stripe not sickle-shaped	19
	b. Spots on the metepisternum small or absent
19a(18b)	a. Mesepisternal pale stripes absent, or represented by small, ill-defined, elongate spots	Aeshna interrupta Walker
	b. Mes- and metepimeral pale stripes either narrow and nearly straight, or divided into upper and lower spots
19b	a. Mesepisternal pale stripes complete, expanded at the posterodorsal ends	20
	b. Mes- and metepimeral pale stripes not divided (mesepimeral stripe may be strongly constricted), relatively wide for at least part of their length and with the anterior margins more or less sinuate or excavated
20a(19b)	a. Frontoclypeal suture with a black band	Aeshna eremita Scudder
	b. Genital valves of ovipositor with lateral carina distinctly broadened basally, distinctly angulate near the midlength, and nearly straight in the apical half
20b	a. Frontoclypeal suture, at most, with a very narrow dark hairline	21
	b. Genital valves of ovipositor with lateral carina not, or barely, broadened basally, and smoothly convex throughout or barely angulate near the midlength
21a(20b)	a. Anterior margin of mesepimeral pale stripe abruptly constricted to form an almost right-angled notch, width at constriction about 1/3 the width of the anteroventral portion of the stripe	Aeshna canadensis Walker
	b. Metepimeral pale stripe abruptly expanded at the posterodorsal end
	c. Genital valves of ovipositor with the lateral ridge weakly developed in the basal 1/3
21b	a. Anterior margin of mesepimeral pale stripe constricted less abruptly to form an obtusely-angled notch, width at constriction about 1/2 the width of the anteroventral portion of the stripe	Aeshna verticalis Hagen
	b. Metepimeral pale stripe gradually expanded at the posterodorsally, with a small notch just before the upper end
	c. Genital valves of ovipositor with the lateral ridge well-developed in the basal 1/3, although lower and more rounded than in distal portion)

Mature Nymphs

1a	a. Antennae with 6 segments, ratio length of Ant3:Ant6 0.83-1.20	Aeshna sitchensis Hagen
	b. Ratio of middorsal length S9:S10 1.03-1.14
	c. Head width 6.5-7.2 mm
	d. Ab6 with posterolateral spine vestigial (<0.24 mm) or absent
1b	a. Antennae with 7 segments, ratio length of Ant3:Ant6 1.25-2.50	2
	b. Ratio of middorsal length S9:S10 1.29-1.58
	c. Head width 7.4-9.5 mm
	d. Ab6 with posterolateral spine well-developed, sometimes <0.24 mm
2a	a. Median lobe-like portion of compound eyes directed medially, diagonal width of compound eye > 0.8x diagonal length	3
	b. Femora either unicolorous or with only faint bands
2b	a. Median lobe-like portion of compound eyes directed posteromedially, diagonal width of compound eye < 0.8x diagonal length	10
	b. Femora usually with 2 or 4 distinct bands
3a(2a)	a. Ab5 with acute posterolateral spine, 0.10-0.40 mm long	Aeshna eremita Scudder
	b. Posterolateral corners of head slightly angular
	c. Prothoracic epaulet angulate in mediodorsal view
	d. Metathoracic femur length = or >7.5 mm
3b	a. Ab5 without acute posterolateral spine	4
	b. Posterolateral corners of head rounded
	c. Prothoracic epaulet rounded in mediodorsal view
	d. Metathoracic femur length < 7.5 mm
4a(3b)	a. Posterolateral spine of Ab6 vestigial, in lateral view at most a short, triangular extension not as long as wide	5
	b. Ratio of Ant3:Ant6 length < 1.7
4b	a. Posterolateral spine of Ab6 elongate-triangular, in lateral view longer than basal width	6
	b. Ratio of Ant3:Ant6 length > 1.7
5a(4a)	a. Palpal blade 1.3-1.6x the basal width of the movable hook, and apical angle of palpal blade abruptly rounded	Aeshna juncea (Linnaeus)
	b. Prothoracic femur length > 4.0 mm
5b	a. Palpal blade 1.1-1.2x the basal width of the movable hook, and apical angle of palpal blade more broadly rounded	Aeshna subarctica Walker
	b. Prothoracic femur length shorter than above, < 4.0 mm
6a(4b)	a. Prementum long, hinge extending to transverse suture of metasternite	Aeshna tuberculifera Walker
	b. Ratio of prementum L:basal W 2.85-3.40
	c. Metathoracic femur length > 7.0 mm
6b	a. Prementum shorter, hinge extending only to mesocoxae	7
	b. Ratio of prementum L:basal W 1.90-2.35
	c. Metathoracic femur length < 7.0 mm
7a(6b)	a. Femora banded with alternate dark and pale blotches, dark markings sometimes faint	Aeshna interrupta Walker
	b. Pattern on dorsum of Ab mostly tan mottled with brown, without defined longitudinal stripes
	c. Ratio of metathoracic femur length : head width > 0.84
	d. Ratio of Ab9 middorsal length : Ab10 middorsal length 1.31-1.38
7b	a. Femora unicolorous, tan or brown	8
	b. Pattern on dorsum of Ab with defined, dark median longitudinal stripe, with adjacent submedian pale stripes and lateral dark stripes
	c. Ratio of metathoracic femur length : head width < 0.84
	d. Ratio of Ab9 middorsal length : Ab10 middorsal length 1.38-1.50
8a(7b)	a. Palpal blade with distal margin truncate and anterolateral corner abruptly rounded	Aeshna verticalis Hagen
	b. Ratio of prementum length : basal width = or > 2.35
	c. Ratio of prementum length : maximum width < 4.5
8b	a. Palpal blade with distal margin rounded, and anterolateral corner slightly to more broadly rounded	9
	b. Ratio of prementum length : basal width < 2.35
	c. Ratio of prementum length : maximum width > 4.5
9a(8b)	a. Anterolateral corner of palpal blade slightly rounded, distal margin partly straight and end tooth small	Aeshna canadensis Walker
	b. Ratio of prementum length : basal width < 2.1
	c. Ratio of of metathoracic femur : prementum length 1.05-1.13
9b	a. Anterolateral corner of palpal blade broadly rounded, distal margin mostly curved and end tooth large	Aeshna clepsydra Say
	b. Ratio of prementum length : basal width > 2.2
	c. Ratio of of metathoracic femur : prementum length 0.98-1.03
10a(2b)	a. Blade of labial palp tapered to slender apex, distal margin curved to end tooth	Aeshna constricta Say
	b. Ratio of prementum length : maximum width 1.13-1.16
	c. Apex of ovipositor of female at, or slightly beyond, Ab10 posteror margin
10b	a. Blade of each labial palp not tapered distally, distal margin truncate	Aeshna umbrosa Walker
	b. Ratio of prementum length : maximum width > 1.20
	c. Apex of ovipositor of female at, or near Ab9 posteror margin, never to Ab10 posterior margin

DuBois RB, Tennessen KJ. 2015. How did E. M. Walker measure the length of the labium of nymphs of Aeshna and Rhionaeschna (Odonata: Aeshnidae)? The Great Lakes Entomologist 48(1-2): 79-92.
Needham JG, Westfall MJ, May ML. 2014. Dragonflies of North America. The Odonata (Anisoptera) fauna of Canada, the Continential United States, Northern Mexico and the Great Antilles. Third Edition. Scientific Publishers: Gainesville, Florida. xiv + 658.
Paulson D. 2011. Dragonflies and damselflies of the East. Princeton Field Guides. Princeton University Press, Pinceton, New Jersey, USA. 538 p.
Tennessen KJ. 2019. Dragonfly nymphs of North America: An Identification Guide. Springer International Publishing, Cham, Switzerland: xiv + 620 p.
von Ellenrieder N. 2003. A synopsis of the Neotropical species of 'Aeshna' Fabricius: the genus Rhionaeschna Förster (Odonata: Aeshnidae). Tijdschrift voor Entomologie 146: 67-207.
Walker EM. 1912. The North American dragonflies of the genus Aeshna. University of Toronto Studies, Biological Series, pp. 1-213.
Walker EM. 1958. The Odonata of Canada and Alaska, Volume 2. University of Toronto Press: Toronto, Ontario, Canada. xii + 318.

Page created: July 17, 1998 - Last updated: April 19, 2020 (EB)