Aquatic Insects of Michigan

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

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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. Fortunately, Walker's (1958) outstanding treatment of the Canadian species works well for Michigan, although some of his metrics were not consistent (DuBois & Tennessen 2015). Species-level determination for immatures often requires precise microscopic measurement.

(Taxonomic References: Paulson 2011, Needham et al. 2014, 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. Small lateral spines on Ab5 as well as Ab6-9 Aeshna eremita Scudder
b. Posterolateral margins of head obtusely angulate
1b a. Lateral spines present only on Ab6-9 or Ab7-9 2
b. Posterolateral margins of head broadly rounded
 
2a(1b) a. Antennae with 6 segments Aeshna sitchensis Hagen
b. Lateral spines of Ab6 absent
also: Muskeg bogs and sphagnum pools
2b a. Antennae with 7 segments 3
b. Lateral spines of Ab6 present, although smaller than those on Ab7-9
 
  a. Blade of labial palp tapering to a slender, slightly curved point  
3a(2b) b. Developing ovipositor of mature female >1.45x the middorsal ventral length of Ab9 Aeshna constricta Say
  a. Blade of labial palp truncate or abruptly hooked, or at least with a distinct subapical shoulder on the anterolateral margin  
3b b. Developing ovipositor of mature female <1.25x the middorsal ventral length of Ab9 4
 
4a(3b) a. Folded prementum elongate and very long, its distal width about 0.55x its length, and posteriorly reaching level with metacoxae Aeshna tuberculifera Walker
b. Developing ovipositor of mature female about 1.2x the mid-dorsal ventral length of Ab9
4b a. Folded prementum stouter, its distal width >0.60x its length, and reaching no farther than the mesocoxae 5
b. Developing ovipositor of mature female <1.13x the middorsal ventral length of Ab9
 
5a(4b) a. Eyes, in dorsal view, widest just anterior to middle, using the posterolateral corner of eye as the posterior limit of measurement Aeshna umbrosa Walker
b. Lateral margins of head, just behind the eye, nearly straight, the lateral portion of margin often dark
c. Femur and tibiae dark with distinct pale light (usually 3) bands
also: Posterior supracoxal processes on pronotum distinctly wider than anterior one; streams, forest lakes and partly shaded pools and ponds
5b a. Eyes, in dorsal view, widest at or just posterior to middle 6
b. Lateral margins of head, just behind the eye, distinctly convex
c. Femur striped or uniform, but tibae not with 3 bands and often uniform
also: Mostly lentic
 
6a(5b) a. Lateral spines of Ab6 absent or vestigial 7
6b a. Lateral spines of Ab6 clearly evident 8
 
7a(6a) a. Blade of each labial palp >1.5x as wide as the moveable hook, both measured at the base of the hook, and with the apical margin truncate Aeshna juncea (Linnaeus)
7b a. Blade of each labial palp <1.5x as wide as the moveable hook, both measured at the base of the hook, and with the apical margin rounded Aeshna subarctica Walker
 
8a(6b) a. Femora with three pale annuli Aeshna interrupta Walker
b. Abdomen with irregular pale blotches on a dark ground color
8b a. Femora uniform in color 9
b. Abdomen with more or less dark median stripe flanked by pale stripes
 
9a(8b) a. Blade of each labial palp squarely truncate, with the outer distal angle very little rounded, the opposing distal margins of the paired lobes parallel Aeshna verticalis Hagen
9b a. Blade of each labial palp not squarely truncate, with the outer distal distinctly rounded, the opposing distal margins of the paired lobes not parallel 10
 
10a(9b) a. Blade of each labial palp terminating in abruptly curved and almost truncate hook Aeshna canadensis Walker
b. Abdomen with a dark median stripe darker around the dorsal cuticular punctures
10b a. Blade of each labial palp terminating in a broadly curved hook Aeshna clepsydra Say
b. Abdomen with a dark median not darker around the dorsal cuticular punctures
 
 

References

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.
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: March 4, 2017 (EB)