Notes - Key - References
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Page last updated: 25 June 1998
Aeshnid larvae are conspicuous, bare-skinned, thin-legged larvae that are widespread in freshwater, found clinging upon aquatic vegetation, stems and other trashy material along and near the waters' edge. Their laterally positioned, well-developed eyes are amongst the largest of all odonates, and are well suited to their clinging habits and aggressive predatory techniques (see Corbet 1962).
These larvae are easily distinguished from other anisopteran larvae by the long, flat mentum, a prementum that is at most slightly cleft (usually not), antennae with at least 6 to 7 segments, and generally smooth abdomen that (except for Nasiaeschna) have no mid-dorsal prominences or hooks. Except for two genera not found in Michigan, the labial palps are without raptorial setae. The abdomen is widest in the middle segments, and appears somewhat triangular or hemispherical in cross-section. Like that of Zygoptera, eggs of adults are laid endophytically (in plant tissue), and the developing genitalia of maturing female larvae are often helpful species-level diagnostic characters. Some aeshnids have direct development, others have significant periods of egg diapause (see Walker 1958, Corbet 1962).
1a. Hind angles of head
decidedly angulate (picture); Ab5-9 with well-developed lateral
spines (picture) - 2
1b. Hind
angles of head rounded (picture); Ab6-9 or 7-9 with well-developed
lateral spines (picture); Aeshna
eremita, which has hind angles of head
bluntly angular (picture), has minute lateral spines on abdominal
segment 5 (picture) - 5
2a.(1a). Abdomen broadly rounded (picture) -
3
2b. Abdomen with distinct middorsal ridge (picture) - 4
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(1)
3a.(2a). Distal margin of palpal lobes truncate (picture);
often with evident pale, dorsal spot on abdominal segment 8, and
paraprocts short, about equal to middorsal length of Ab9+10 -
Boyeria
3b. Distal
margin of palpal lobes ending in curved tips (picture); no evident
spot on abdominal segment 8, and paraprocts longer, length greater
than middorsal length of Ab9+10 - Basiaeschna janata
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(2); Back to beginning of
key
4a.(2b). Low median ridge on dorsum of abdomen with blunt
hooks on Ab7-9 (picture); palpal lobe rounded at tip (picture) -
Nasiaeschna
pentacantha
4b. Low median ridge on dorsum of abdomen without blunt hooks on Ab7-9 (picture); palpal lobe truncate at tip (picture) - Epiaeschna heros
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(2); Back to beginning of
key
5a.(1b). Antennae longer than distance from their base to
rear of head (Figure 5a1); distal margin of ligula deeply bilobed,
with a V-shaped notch (Figure 5a2) - Gomphaeschna
furcillata
Fig.5a1
Fig.5a2
Fig. 5a1: Gomphaeschna
furcillata exuvia (6x, dorsal
view), from tupelo swamp west of Walkertown, Hardin Co., Tennessee,
collected on 01 April 1986 by K. J. Tennessen. Image from specimen
kindly loaned by K. J. Tennessen.
Fig. 5a2: Ibid, (12.5x, ventral view).
5b. Antennae
about half as long as distance from their base to rear of head
(picture); distal margin of ligula obtuseangulate, at most very
slightly bilobed, with the notch closed (picture) - 6
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key
6a.(5b). Truncated blade of lateral lobe with prominent end
hook (picture); compound eyes as long as their greatest width
(picture); mentum 2 or more times as long as width at base (picture);
paraprocts about equal to Ab8+9 (picture) - Anax
6b. End hook not prominent (picture); compound eyes much shorter than their greatest width (picture); mentum < 1.5 times as long as width at base (picture); paraprocts shorter than above, about equal to Ab9+10 (picture) - Aeshna
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Corbet, P. S. 1962. A biology of dragonflies. E. W. Classey Ltd.: Oxon, England. xvi + 247 pp.
Walker, E. M. 1958. The Odonata of Canada and Alaska, Vol. 2. University of Toronto Press: Toronto. xii + 318.
Westfall, M. J., and K. J. Tennessen. 1996. Odonata, pp. 164-211. In An Introduction to the Aquatic Insects of North America, 3rd Ed. Merritt, R. W. and K. W. Cummins (eds.). Kendell/ Hunt Publishing Company: Dubuque, Iowa.