Aeshna is the most speciose holarctic genus of Aeshnidae, and twelve species occur in Michigan (see maps below). As adults are strong fliers, most of our species - A. canadensis, A. clepsydra, A. constricta, A. interrupta, A. tuberculifera, A. umbrosa and A. verticalis - 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 S 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, which was separated from the genus Aeshna by Ellenreider (2003) is a member of a primarily Neotropical group which also includes R. multicolor (Hagen) in the western US. The spatterdock darner has been found only in the southern part of the LP. It has been kept with the other members of Aeshna in this key.
Larvae usually are found clinging to vegetation in lakes and ponds as well as 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 Aeshna individuals together with other aquatic invertebrate organisms.
With some rather subjective determinations of diagnostic features, some earlier keys for aeshnid larvae (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, and the key below is modified from the wealth of information provided in that work as well as from measurements of larval specimens here at UMMZ. Species-level determinations often requires a microscope with an eyepiece equipped with measuring graticule to permit accurate measurement of labium width-to-length ratios as well as the length of female larvae' developing genital structures.
Other links with information on the biology or
ecology of larval Aeshna:
Ottawa, Ontario survey, with brief habitat notes >> http://www.cyberus.ca/~jdsankey/odon2.html
Abstract from faunal survey in Szigetköz, Hungary >> http://origo.hnm.hu/danube_dg/e5ambrus.html
Brief habitat notes from New Jersey, USA >> http://www.hsrl.rutgers.edu/cumb.cape.html
Study examining effects of contaminant-bound sediments on Aeshna larvae's predation efficiency >> http://www.ecotox.lu.se/ECOTOX/th_met.html
1a. Palpal lobes tapering to slender, slightly curved points (picture); female genitalia of mature larvae very long, > 1.45x the mid-dorsal ventral length of Ab9 - A. constricta
lobes abruptly hooked, or truncate (picture); female genitalia
shorter than above, < 1.40x the mid-dorsal vental length of Ab9 -
2a.(1b). Antennae 6-segmented; no lateral spine on Ab6 ; female genitalia of mature larvae about 1.3x the mid-dorsal ventral length of Ab9; muskeg bogs and sphagnum pools - A. sitchensis
7-segmented; lateral spine on abdominal segment 6; female genitalia
< 1.25x the mid-dorsal ventral length of Ab9 - 3
Back to previous couplet (1)
3a.(2b). Lateral spine on Ab5 (may be minute) (picture); posterolateral margin of head somewhat obtuse-angulate (picture) - A. eremita
3b. No lateral
spine on Ab5 (picture); posterolateral margin of head rounded
(picture) - 4
Back to previous couplet (2); Back to beginning of key
4a.(3b). Folded labium elongate and very long, its distal width about 0.55x its length, and posteriorly reaching level with hind coxa (picture); female genitalia of mature larvae about 1.2x the mid-dorsal ventral length of Ab9 (picture); usually resident of bog ponds - A. tuberculifera
labium stouter, its distal width > 0.60x its length (picture), and
reaching no farther than the middle coxa; female genitalia < 1.13x
the mid-dorsal ventral of Ab9 -
Back to previous couplet (3); Back to beginning of key
5a(4b). Labium long and narrow, width in folded position < 0.63x its length (picture); femur and tibiae dark with distinct pale light (usually 3) bands (picture); eyes widest in front of middle (using posterolateral margin of eye as posterior limit of measurement) (picture); postocular margin of head straight (picture); streams, forest lakes and partly shaded pools and ponds - A. umbrosa
wider, > 0.63x it length (picture); femur striped or uniform, but
tibae not with 3 bands and often unifrom (picture); eyes widest at
or slightly behind middle (picture); postocular margin of head
slightly convex (picture) - 6
Back to previous couplet (4); Back to beginning of key
6a.(5b). Width of folded labium 0.78-0.80x of its length; southern LP, woodland swamps and bog-margined pools - Rhionaeschna mutata
6b. Width of
folded labium < 0.75x of its length, usually < 0.70x (picture)
Back to previous couplet (5); Back to beginning of key
7a.(6b). Femora dark with three pale annuli (can fade with older specimens), tibiae may also have pale banding (picture); abdomen marked with irregular pale blotches on a darker ground color (picture); dark submarginal blotch behind eye (picture) - A. interrupta
uniform (picture); abdomen more or less distinctly marked with dark
median longitudinal stripe bordered by pale stripes (picture);
submarginal blotch behind eye, if present, paler (picture) -
Back to previous couplet (6); Back to beginning of key
8a.(7b). Lateral spine on Ab6 vestigial (picture); longitudinal stripes of abdomen somewhat broken into segmental spots, not always distinct, the dark median strip no darker than the lateral dark areas (picture) - 9
spine on Ab6 small but not vestigial (picture); longitudinal stripes
of abdomen clear-cut, the median stripe usually darker than the
lateral dark areas (picture) - 10
Back to previous couplet (7); Back to beginning of key
9a.(8a). Palpal lobes > 1.50x as wide as the movable hook at its basal articulation, the distal margin squarely truncate and the outer distal angle little rounded (picture); cerci of male about 0.33x longer than male projection of epiproct, their apices very slightly incurved (picture); general surface dull (picture) - A. juncea
lobes < 1.50x as wide as the movable hook at its basal
articulation, the outer distal angle broadly rounded (picture); cerci
of male about 0.50x longer than the male projection, their apices
decidedly incurved (picture); general surface polished (picture) -
Back to previous couplet (8); Back to beginning of key
10a.(8b). Palpal lobes squarely truncate with outer distal angle very little rounded, the opposing distal margins of the paired lobes parallel (picture) - A. verticalis
lobes not squarely truncate, the outer distal distinctly rounded, the
opposing distal margins of the paired lobes not parallel (picture) -
Back to previous couplet (8); Back to beginning of key
11a.(10b). Palpal lobes each terminating in a very abruptly curved and almost truncate hook (picture) dark median stripe deepened about the dorsal punctata (picture) - A. canadensis
lobes each terminating in a broadly curved hook (picture); dark
median stripe of abdomen not deepened about the dorsal punctata
(picture) - A. clepsydra
Back to previous couplet (10); Back to beginning of key
Ellenreider, Von N. 2003. A synopsis of the Neotropical species of "Aeshna" Fabricius: The genus Rhionaeschna Forster (Odonata: Aeshnidae). Tijdsch. voor Entomologie. 146:67-207.
Fabricius, J. C. 1775. Systema entomologiae. Libraria Kortii: Flensburg & Leipzig. 424 pp.
Hagen, H. A. 1861. Synopsis of the Neuroptera of North America, with a list of the South American species. Smithsonian Miscellaneous Collections 4:1-347.
Linne, C. 1758. Systema naturae. Editio decima reformata. Holmiae. 543 pp.
Needham, J. G. and M. J. Westfall, Jr. 1955. A Manual of the Dragonflies of North America (Anisoptera). University of California Press: Berkeley, California. xii + 615 pp.
Say, T. 1839. Descriptions of new North American neuropterous insects and observations on some already described by (the late) Th. Say. Journal of the Academy of Natural Science of Philadelphia 8:9-46.
Scudder, S. H. 1866. Notes on some Odonata from the White Mountains of New Hampshire.Proceedings of the Boston Society of Natural History 10:211-222.
Walker, E. M. 1908. A key to the North American species of Aeshna found north of Mexico. The Canadian Entomologist 40(11):377-391, (12):450-451, pl. 10.
Walker, E. M. 1958. The Odonata of Canada and Alaska, Vol. 2. University of Toronto Press: Toronto. xii + 318.