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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Coenagrionidae of Michigan - Identification

[under construction]

Our largest family of damselflies in terms of species (32) and genera (7), coenagrionids are ubiquous in almost all aquatic systems in our state. Although not particularly strong flyers, adults of some species are often found quite some distance away from water bodies. Nymphs are more common in lentic systems, but many are found among the macrophytes and other growth in quieter or backareas of streams and rivers. Some are adapted to flowing water (Argia, some Enallagma). Life cycles are generally univoltine, though further north some may require an additional year of development, and others (e.g., Ischnura, Enallagma) may even have multiple generations per year in the south.


References: Tennessen 2006, Walker 1953, Westfall and May 2006

Key to Adults

1a a. Tibial spurs twice the length of the intervening spaces, at least proximally 2
1b a. Tibial spurs at most barely longer than the intervening spaces 3

2a(1a) a. Vein M1A extending at least the length of 8 cells b. M2 arising near the 6th or 7th postnodal crossvein in the forewing, near the 5th or 6th crossvein in the hindwing c. Wings petiolated only to level of the 1st antenodal crossvein Argia
2b a. Vein M1A extending at most the length of 5 cells b. M2 arising near the 5th postnodal crossvein in the forewing, near the 4th crossvein in the hindwing c. Wings petiolated to level beyond the 1st antenodal crossvein Nehalennia (in part)

3a(1b) a. Intersternum with a prominent, moundlike tubercle bearing numerous long, stiff setae b. Wings long, nearly equal in length to the abdomen c. Stocky, red to reddish brown and black Amphiagrion
3b a. No prominent intersternal tubercle present b. Wings shorter, at most 3/4x length to the abdomen c. Usually not stocky, usually colored differently 4

4a(3b) a. Dorsum of thorax and abdomen mostly metallic green b. Abdominal length 19-25mm c. Prothoracic femora with 2 distinct external black stripes, 1 at base of spines Nehalennia (in part)
4b a. Dorsum of thorax and abdomen usually not metallic green b. Abdominal length variable c. Prothoracic femora without a black stripe, or with one black stripe that may cover the entire external surface 5

5a(3b) a. Postocular area dark, without pale spots, although crest crest of occiput may be pale Chromagrion conditum (Hagen, in Selys)
5b a. Postocular area entirely pale or with pale spots ranging from narrow linear areas to large round spots, sometimes confluent with each other or with pale crest of occiput 6

6a(5b) a. Vein M2 arising proximal to or near the 4th postnodal crossvein in fore wing, and proximal to or near 3rd postnodal in hind wing 7
6b a. Vein M2 arising near 5th postnodal crossvein or beyond in fore wing, near 4th or beyond in hind wing 8

7a(6a) a. Black humeral stripe divided along its entire length by a narrow, pale stripe b. Prothorax with a pale dorsomedial spot Enallagma (in part)
7b a. Black humeral stripe entire along its length or lacking b. Prothorax without a pale, dorsomedial spot or entirely pale Ischnura (in part)

8a(6b) a. Anal crossing links Cu to the posterior border in the fore and hind wings Enallagma (in part)
8b a. Anal crossing links Cu to A in fore and usually the hind wings, and does not reach the posterior border 9

9a(8b) a. Males
9b a. Females

10a(9a) a. Pterostigma of fore wing different in shape, color, or size from pterostigma of hind wing b. Ab10 with a posterodorsally projecting bifid process at least one-half as long as the segment Ischnura (in part)
10b a. Pterostigma of fore and hind wings similar in color, shape, and size b. Ab10 with at most a very low, widely bifid prominence one-fourth as long as the segment Coenagrion, Enallagma (in part)

11a(10b) a. Humeral suture usually pale, but, if a black stripe present, then no apical spine on venter of Ab8 Ischnura (in part)
11b a. Humeral suture usually with a black stripe, but, if pale, then an apical spine is present on venter of Ab8 12

12a(11b) a. Ab8 without a ventroapical spine Coenagrion
12b a. Ab8 with a ventroapical spine Enallagma (in part)

Key to Mature Nymphs

1a a. Body shape usually short and stout b. Premental setae absent c. Palpal lobes ending in two distal, pointed hooks d. Palpal setae 0-3 also: Principally lotic Argia
1b a. Body shape usually longer and more slender b. Premental setae present c. Palpal lobes ending in one distal, pointed hook and a truncate, denticulate lobe d. Palpal setae 3 or more also: Usually lentic 2

2a(1b). Posterolateral margins of head sharply angulate 3
2b. Posterolateral margins of head broadly rounded 4

3a(2a) a. Apices of gills with the acute tip long and sharply pointed b. Gills narrower, their maximum width about 1/6x that of gill length, their margins with widely separated setae c. Antennae 7-segmented Chromagrion conditum (Hagen)
3b a. Apices of gills with the acute tip not long or sharply pointed b. Gills wider, their maximum width about 1/3x that of gill length, their margins with thickly and closely spaced setae c. Antennae with 5-6 segments Amphiagrion saucium (Burmeister)

4a(2b) a. One premental setae of normal length present, although 1-3 small setae may be present on its medial side 5
4b a. At least two setae of normal length present 6

5a(4a) a. Palpal setae 3-4 b. Numerous, long, stiff setae on the lateral carinae of all abdominal segments beyond Ab1 c. Total length (not including gills) usually 17mm or more Enallagma (in part)
5b a. Palpal setae 5-6 b. No long, stiff setae present on the lateral carinae of anterior abdominal segments, although often present on posterior segments c. Total length 15mm or less Nehalennia

6a(4b) a. Lateral carinae of Ab2-8, in dorsal view, slightly concave, with their apexes prominent and bearing two or more stout, curved setae b. Usually 3 premental setae present c. Eyes with a dark pattern of spots, or lines forming hexagonal-shaped cells Enallagma (in part)
6b a. Leteral carinae of Ab2-8 with margins straight or only slightly convex, apexes not prominent, and with apical setae, if present, not noticeably larger than the preceding setae c. 2-5 premental setae present d. Eyes, if patterned, usually not as above 7

7a(6b) a. Eyes usually with a pattern of lateral, alternating pale and dark bands b. Antennae usually with 7 distinct segments c. Lateral carinae of Ab2-7 with numerous small setae not arranged in a single row Ischnura
7b a. Eyes with no such pattern of lateral pale and dark bands, although dark spots may be apparent b. Antennae 6 or 7-segmented, last (apical) segment sometimes with a diffuse, unclear suture that may be ringed with thin setae making it appear separated c. Lateral carinae of Ab2-8 usually with a single row of setae of variable stoutness Coenagrion and Enallagma (in part)

Page last edited: February 12, 2017 (EB)