Coenagrion Kirby, 1890 and Enallagma Selys, 1875 (Coenagrionidae) - Bluets

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Notes on the Michigan Species of Coenagrion and Enallagma

Enallagma is a widespread genus of coenagrionids that is most speciose in North America, with16 species now recorded in Michigan. Coenagrion is chiefly a palearctic genus in which three species occur in North America, with 2 two species occuring here. Larvae are diagnostically a difficult group of damselflies. Only mature specimens with intact caudal gills can be identified to species, and the works (Walker 1953; Westfall and May 1996) upon which the key below is based caution about the reliability of keys. These moderate-sized damselflies closely resemble the larvae of Ischnura and Coenagrion, and diagnostic keys (Walker 1953, Westfall and May 1996) upon which our key is based distinguish Coenagrion and Enallagma only at the species-level.

There is considerable debate regarding the viability of E. vernale Gloyd (1943), which Donnelly (1989) synomized with E. cyathigerum. Recent information and examination of material as well as data from habitat separation (the former inhabit lakes and rivers, the later principally bogs and heavily vegetated ponds) may indeed support the distinct identity argued for by Gloyd. Refer to Walker (1953) to distinguish between these two.

Most species inhabit lakes, ponds and wetlands as well as slower portions of streams and rivers, usually with abundant aquatic vegetation. E. anna, E. aspersum, E. basidens, E. divagans, and E. traviatum are known only from the LP. Both E. anna and E. basidens appear to be expanding their ranges throughout North America, being found in sheltered coves and edges of large lakes, small ponds and slow portions of streams, as well as human-impacted habitats such as impoundments and quarry ponds (Cannings 1989, O'Brien and Pratt, in press). E. antennatum, E. exsulans, E. geminatum, E. signatum and E. vesperum are known in the UP only from one record, but are widespread in the LP. The other species (E. boreale, E. carunculatum, E. civile, the circumpolar E. cyathigerum, E. ebrium, and E. hageni) are widespread in both peninsulas. (See maps below).

Population cohorts for several species have been studied, though little generic-level concensus has been reached. Baker and Clifford (1982) studied a population of E. boreale in a boreal forest pond in Alberta, Canada, and concluded that low temperatures during egg development strongly influenced subsequent growth of larvae, ultimately determining if there were one or two cohorts per year. Existence of mixed cohorts (bivoltine and uni- or multivoltine) has also been observed for E. aspersum in North Carolina (Ingram and Jenner 1976) and E. cyathigerum in Britain (Macan 1964). The latter species also was found to be univoltine at another site in Britain (Johannsson 1978), and Kormondy and Gower (1965) found E. ebrium to be univoltine in Pennsylvania as well. Pearlstone (1973) studied the feeding behavior of E. boreale in a small lake in southwestern British Columbia. Cladocerans and larval chironomids were the principal prey items, although larvae appeared opportunistic with prey choice as other prey items were consumed (e.g., mayflies, stoneflies, water mites, copepods, other damselflies, etc.). Prey choice also did not marked change among the various instars of mature instars.

Ecological information on the larvae of Coenagrion comes principally from Walker (1953), Baker and Clifford (1980) and Cannings and Cannings (1980). Larvae are widely distributed in northern latitudes, and is probably univoltine in Michigan. Walker (1953, p. 179) notes that C. resolutum, which is widely distributed in Michigan (Map 1, below), inhabits a wide variety of lentic habitats, including "almost any small permanent or subpermanent body of still water...ordinary ponds and prairie sloughs with marshy borders; in springy cat-tail marshes; in dark calla ponds; in sphagnum pools, in cool northern spruce or tamarack swamps, and in the marginal vegetation of slow weedy streams." C. interrogatum, which is found only in the northernmost part of Michigan, appears locally distributed in open fens and marshes with abundant mosses (Cannings and Cannings 1980).

Other links with information on the biology or ecology of larval Coenagrion and Enallagma:
Shetland, Scotland E. cyathigerum habitat information >>http://www.zetnet.co.uk/sigs/insects/dragon.html
Houston, Texas Enallagma with brief habitat notes >> http://www.io.com/~pdhulce/dragon3.html
McPeek Enallagma research >> http://math.grin.edu/~brownj/374_Q3.html
Introduced Enallagma civile to Hawaii >> http://www.bishop.hawaii.org/bishop/ento/Megalagrion/htmlPages/Mega01.shtml

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Michigan Species List

Coenagrion


Map 1: County distribution of Coenagrion resolutum in Michigan
Click on map for a larger image

Coenagrion interrogatum (Selys, 1876) - Subarctic Bluet
Coenagrion resolutum (Selys, 1876) - Taiga Bluet - Map 1

Enallagma

Map 1 Map 2 Map 3 Map 4 Map 5 Map 6 Map 7 Map 8 Map 9 Map 10 Map 11 Map 12 Map 13 Map 14 Map 15
Maps 1-15: County distribution for the Michigan species of
Enallagma
Click on map for a larger image

Enallagma anna Williamson - map under construction
Enallagma antennatum (Say, 1839) - rainbow bluet - Map 1
Enallagma aspersum
(Hagen, 1861) - azure bluet - Map 2
Enallagma basidens
Calvert, 1902 - double-striped bluet - Map 3
Enallagma boreale Selys, 1875 - boreal bluet - Map 4
Enallagma carunculatum
Morse, 1895 - tule bluet - Map 5
Enallagma civile
(Hagen, 1861) - familiar bluet - Map 6
Enallagma annexum
(Hagen, 1861) - northern bluet - Map 7
Enallagma divagans
Selys, 1876 - turquoise bluet - Map 8
Enallagma ebrium
(Hagen, 1861) - marsh bluet - Map 9
Enallagma exsulans
(Hagen, 1861) - stream bluet - Map 10
Enallagma geminatum
Kellicott, 1895 - skimming bluet - Map 11
Enallagma hageni
(Walsh, 1863) - Hagen's bluet - Map 12
Enallagma signatum
(Hagen, 1861) - orange bluet - Map 13
Enallagma traviatum
(syn. westfalli) Selys, 1876 - slender bluet - Map 14
Enallagma vesperum
Calvert, 1919 - vesper bluet - Map 15

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Key to Mature Larvae of Michigan Coenagrion and Enallagma
(Adapted from
Walker 1953 and Westfall and May 1996)

Caution: only mature specimens with intact lateral and medial gills can be reliabily identified to species unless an associated adult specimen is available.

1a. Second antennal segment longer than first, third segment at least 2x longer than first (Fig. 1); stout dorsal antenodal setae of median gill in complete row, if present, although may be proximally minute (Fig. 2); gills with pigment usually restricted to the tracheae, sometimes with 1-3 indistinct transverse stripes and/or an axial stripe (picture); eyes usually unpatterned (Fig. 4) - 2

Fig. 1 Fig. 2 Fig. 4
Fig. 1:
Enallagma ebrium larva (25x, dorsal-lateral view), from Douglas Lake, Cheboygan Co., Michigan, collected by E. J. Kormondy on 19 June 1953. UMMZODO-2000. Fig. 2: same specimen as in Fig. 1 (25x, lateral view). Fig. 4: same specimen as in Fig. 1 (12x, dorsal view).

1b. Second antennal segment not longer than first, third segment < 2x longer than first (picture); stout dorsal antenodal setae of median gill whole or partly reduced to slender hairs or confined to the vicinity of the nodus (picture); gills generally more extensively pigmented (picture); eyes usually patterned with dark stripes or spots (picture) - 14


2a.(1a). Gills with patches of closely branched and deeply pigmented tracheae, the intervening areas with mostly unpigmented and much less branched tracheae (picture) - 3

2b. Gills with the tracheae uniformly and usually much less closely branched, pigmentation of the tracheae general although often interrupted by clear areas (picture) - 4
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3a.(2a). Cerci of male in dorsal view bluntly angular, the outer edge nearly straight and with an oblique ridge, in lateral view bluntly rounded (picture); female apparently indistinguishable from E. hageni - E. ebrium

3b. Cerci of male in dorsal view with an evenly curved margin and without a ridge, in lateral view bluntly angular (picture) - E. hageni
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4a.(2b). Dorsal antenodal setae of median gill fewer than 20 (picture); cerci of male with deep dorsal concavity, easily visible in dorsolateral view, sometimes even with dorsal margin appearing concave in strict lateral view (picture), and in dorsal view subacute, slightly longer than wide (picture); median gill usually < 4.5 mm - E. geminatum

4b. Dorsal antenodal setae almost always 20 or more (picture); cerci of male with concavity, if any, medial or slightly dorsomedial, not usually visible in dorsolateral view (picture) and, if visible, cerci in dorsal view appear more or less globular and wider than long (picture); median gill usually > 4.5 mm - 5
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5a.(4b). Dorsal and ventral series of stout antenodal setae of median gill nearly equal in length and consisting of rather closely set setae (picture) - 6

5b. Dorsal and ventral series of stout antenodal setae of median gill nearly 2x as ventral series, with the latter consisting of comparatively small and widely spaced setae (picture) - 7
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6a.(5a). Cerci in caudal view more rounded distally, in the male shaped like clenched boxing gloves seen end-on, the distal projection more than 0.5 as wide (from dorsomedial to ventrolateral face) as long (picture); cerci in female with distal projection usually higher than wide, set off from basal portion by a dorsal fold only (picture) - E. boreale

6b. Cerci in caudal view less rounded distally, in the male with the distal projection forming a distinct, transverse ridge that is less than 0.5 as wide as long (measured from above); cerci in female with the distal projection usually not higher than wide and set off from the basal portion by dorsal and ventral folds (picture) - E. annexum
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7a.(5b). Males, ovipositor rudiments absent (picture) - 8

7b. Females, ovipositor rudiments present (picture) - 11
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8a.(7a). Cerci very large and robust, in dorsal view > 0.38mm in length; dorsal antenodal series of setae of median gill usually extending at least 2/3 the length of the gill - E. anna

8b. Cerci slenderer, in dorsal view < 0.35mm in length; antenodal setae of gills variable - 9
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9a.(8b). Ventral surface of cerci strongly concave in ventrolateral view (picture); bog-ponds - E. aspersum

9b. Ventral surface of cerci broadly convex in ventrolateral view (picture) - 10
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10a.(9b). Cerci in posterior view with maximum distance from dorsomedial to ventrolateral margins greater than maximum distance from dorsolateral to ventromedial margins (picture); cerci usually < 0.3 mm long in dorsal view (picture) - E. carunculatum

10b. Cerci in posterior view with maximum dorsomedial to ventrolateral margins less than maximum dorsolateral to ventromedial distance (picture); cerci usually > 0.3 mm in dorsal view (picture) - E. civile
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11a.(7b). Length of cerci in dorsal view 0.29 mm or more - 12

11b. Length of cerci in dorsal view 0.28 mm or less - 13
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12a.(11a). Cerci with medial margin distinctly concave in ventrolateral view - E. civile

12b. Cerci with medial margin straight or barely concave in ventrolateral view - E. anna


13a.(11b). Cerci with medial margin slightly concave in ventrolateral view (picture); axial tracheae of gills often appearing distinctly coiled around each other basally (picture) - E. aspersum

13b. Cerci with medial margin usually straight or convex, rarely very slightly concave, in ventrolateral view (picture) axial tracheae usually not appearing distinctly coiled around each other basally (picture) - E. carunculatum
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14a.(1b). Posterolateral margin of head rounded, at best with small lobes (picture); lateral carinae of abdomen projecting abruptly from the posterior part of each segment, but not prominent in front, the posterior margin bearing a group of stout setae but otherwise bare (picture); gills without patches of closely branched and deeply pigmented tracheae (figure) - 15

14b. Posterolateral margin of head with prominent lobes (picture); lateral carinae of abdomen evident but not projecting abruptly from the posterior part of each segment, and (except E. basidens) bearing only slender hairs and, if any, few stout setae (figure); gills usually with patches of closely branched and deeply pegment tracheae (figure) - 16
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15a.(12a). Dorsal margin of median gill without prominent stout setae (figure); median gill at most 3x as long as its greatest width, in lateral view distal 2/3 greatly expanded with dorsal margin strongly convex (figure); tracheae of gills widely spaced, usually directly opposite and perpendicular to the axis (figure) - E. vesperum

15b. Dorsal margin of median gill with at least a few stout setae proximal to the nodus (figure), number of stout setae on ventral margin of lateral gills 45 or more, stout setae on lateral carina 30-40 (figure); median gill at least 3x as long as its greatest width, and widening gradually from the base with the dorsal margin not so strongly convex (figure); tracheae more numerous than above, meeting axis at an acute angle (figure) - E. signatum
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16a.(12b). Median gill (lateral gills often similar) with 2-4 apical, dark, transverse bands often confluent with axis (figure); lateral carinae of abdomen projecting rather abruptly from posterior part of each segment, with a scattered group of stout setae on the prominence (figure); body length not including gills usually < 11 mm - E. basidens

16b. Median gill without such dark apical bands, although an irregular and diffuse dark area may be present (figure); lateral carinae of abdomen prominent but not projecting abruptly from the end of each segment, and generally bearing many slender hairs but few stout setae (figure); body length not including gills usually > 11 mm - 17
Back to previous couplet (14); Back to beginning of key


17a.(14b). Gills without a distinct nodus or abrupt color change beyond midlength, but with 4 or 5 widely spaced dark bands formed by patches of closely brnached and darkly pigmented tracheae (figure); gills narrow, at least 6x long as wide (figure) - E. divagans

17b. Gills with distinct abrupt color change (dark proximally, light distally) about 1/3 to 1/2 the distance from the apex (figure); gills wider, usually 4-6x long as wide (except E. antennatum) - 18
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18a.(15b). Median gill with stiff dorsal setae absent or indistinct (figure); gills usually dark brown from base to nodus which is located 1/2 to 2/3 from base to apex (figure) - E. traviatum

18b. Median gill usually with distinct stiff dorsal setae proximal to nodus (except E. antennatum) (figure); gills proximal to nodus usually less deeply pigmented or with pigment restricted to basal and axial areas (figure) - 19
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19a.(16b). Median gill without stiff, dorsal antenodal setae, and without a definite nodus (figure); lateral gills very narrow, 6-8x long as wide - E. antennatum

19b. Median gill with 8-12 stiff, dorsal antenodal setae, and gill with a distinct nodus 1/2 the distance from base to apex (figure); lateral gills wider, 4-5x long as wide - E. exsulans
Back to previous couplet (18); Back to beginning of key

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References

Baker, R. L., and H. F. Clifford. 1982. Life cycle of an Enallagma boreale Selys population from the boreal forest of Alberta, Canada (Zygoptera: Coenagrionidae). Odonatologica 11(4):317-322.

Calvert, P. P. 1902, in Calvert, P. P. 1901-1908. Odonata. In Biologia Centrali Americana: Insecta Neuroptera. R. H. Porter & Dulau & Co.: London. Dec 1902, p. 114.

Calvert, P. P. 1919. Gundlach's work on the Odonata of Cuba: a critical study. Transactions of the American Entomological Society 45:335-396.

Cannings, R. A. 1989. Enallagma basidens Calvert, a dragonfly new to Canada, with notes on the expansion of its range in North America (Zygoptera: Coenagrionidae). Notulae Odonatologicae 3(4):53-55.

Cannings, S. G., and R. A. Cannings. 1980. The larva of Coenagrion interrogatum (Odonata: Coenagrionidae), with notes on the species in the Yukon. The Canadian Entomologist 112:437-441.

Charpentier, T. de. 1840. Libellulinae europaeae descriptae e depictae. Lipsiae, Leopold Voss. 180 pp.

Donnelly, T. W. 1989. The status of Enallagma cyathigerum (Charp.) and E. vernale Gloyd in south-central New York (Zygoptera: Coenagrionidae). Odonatologica 18:373-378.

Gloyd, L. K. 1943. Enallagma vernale, a new species of Odonata from Michigan. Occasional Papers of the Museum of Zoology, University of Michigan 479:1-8.

Hagen, H. A. 1861. Synopsis of the neuroptera of North America, with a list of the South American species. Smithsonia Miscellaneous Collections 4:1-347.

Ingham, B. R., and C. E. Jenner. 1976. Life histories of Enallagma hageni (Walsh) and E. aspersum (Hagen) (Zygoptera: Coenagrionidae). Odonatologica5:331-345.

Johannsson, O. E. 1978. Co-existence of larval Zygoptera (Odonata) common to the Norfolk Broads (U.K.). Oecologia 32:303-321.

Kellicot, D. S. 1895. Catalogue of the Odonata of Ohio, Part 1. Journal of the Cincinnati Society of Natural History 17:195-216.

Kirby, W. F. 1890. A synonymic catalog of Neuroptera Odonata or dragonflies. Guerney and Jackson, London. 202 pp.

Kormondy, E. J., and J. L. Gower. 1965. Life history variations in an association of Odonata. Ecology 46:882-886.

Macan, T. T. 1964. The Odonata of a moorland fishpond. Int. Revue ges. Hydrobiol. 49:325-360.

McPeek, M.A. 1998. Comments on Enallagma cyathigerum and vernale. Argia 10(1):22-23

Morse, A. P. 1895. New North American Odonata. Psyche 7:207-211.

O'Brien, M.F. and Paul D. Pratt. 1999. Enallagma anna, a damselfly new to the Great Lakes Region (Odonata: Coenagrionidae). The Great Lakes Entomologist 31(3&4):211-213.

Pearlstone, P. S. M. 1973. The food of damselfly larvae in Marion Lake, British Columbia. Selysia 6:33-39.

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.

Selys-Longchamps, E. de. 1875. Notes on Odonata from Newfoundland collected in 1874 by Mr. John Milne. Entomologists Monthly Magazine 11:241-243.

Selys-Longchamps, E. de. 1876. Synopsis des agrionines, cinquième légion: Agrion (suite). Le genre Agrion. Bulletin de l'Académie royale des Sciences de Belgique (2) 42:480-531.

Walker, E. M. 1953. The Odonata of Canada and Alaska, Vol. 1. University of Toronto Press: Toronto, Ontario. xi + 292 pp.

Walsh, B. D. 1862. List of the Pseudoneuroptera of Illinois contained in the cabinet of the writer, with descriptions of over forty new species, and notes on their structural affinities. Proceedings of the Entomological Society of Philadelphia 1862:361-402.

Walsh, B. D. 1863. Observations on certain N. A. neuroptera by Hagen, M. D., of Konigsberg, Prussia; translated from the original French MS., and published by permission of the author, with notes and descriptions of about twenty new N. A. species of Pseudoneuroptera. Proceedings of the Entomological Society of Philadelphia 2:167-272. [note: see also Walsh, B. D. 1862 for original description of adults, which were named in Walsh 1863. Source: Westfall and May 1996 ).

Westfall, M. J., Jr. and M. L. May. 1996. Damselflies of North America. Scientific Publishers: Gainesville, Florida. x + 650 pp.

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