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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Libellulidae (Skimmers) of Michigan - Identification

Introduction

[under construction]

References: Needham et al. 2010, Tennessen 2006, Walker 1975

Key to the Adults

    1a

    a. Forewing triangle with anterior side angulate

    Nannothemis bella (Uhler)
    b. Anal loop insdistinct, open to rearward
    c. Very small dragonflies, wings hyaline and <16mm in length
    1b a. Forewing triangle with anterior side straight 2
    b. Anal loop distinct, closed at toe
    c. Larger dragonflies, wings >16mm, if short, then either deep yellow or strongly patterned with brown
     
    2a(1b) a. Pterostigmata trapezoidal, each with proximal and distal margins widely divergent anteriorly, the proximal margin nearly perpendicular to the costa and vein R1 3
    b. Hindwings each with nodus positioned closer to wing base than the pterostigma
    c. Hindwings usually very widely expanded basally, usually with at least 5 cell rows between wein A2 and anal angle of wing, with several unusually elongated cells near wing margin anterior to anal angle
    d. Vein Appl usually well-developed
    2b a. Pterostigmata usually not trapezoidal, each with proximal and distal margins approximately parallel to each other and both oblique to costa and vein R1 4
    b. If pterostigmata somewhat trapezoidal, then hindwings each with nodus closer to the base of the pterostigma than to the wing base
    c. Hindwings not usually expanded basally, usually with no more than 4 cell rows between wein A2 and anal angle of wing, without unusually elongated cells near wing margin anterior to anal angle
    d. Vein Appl absent or poorly developed
     
    3a(2a) a. Hindwings with two cubito-anal crossveins Pantala
    b. Veins M2 and Rs strongly undulate
      a. Hindwings with one cubito-anal crossveins Tramea
    b. Veins M2 and Rs not strongly undulate
     
    4a(2b) a. Midvein of anal loop angulated < 30° at ankle 5
    4b a. Midvein of anal loop angulated distinctly more than 30° at ankle 6
     
    5a(4a) a. Forewing triangles with anterior side nearly as long as the proximal side Perithemis tenera (Say)
    b. Sexually dimorphic, wings of male deep amber yellow with little or no brown, wings of female usually with extensive brown markings but mostly hyaline in the distal 1/4-1/3
    c. Hindwings usually shorter than 22mm
    5b a. Forewing triangles with anterior side only about 1/2 as long as the proximal side Celithemis
    b. Usually not strongly sexually dimorphic, wings often with extensive brown markings but never amber without brown markings
    c. Hindwings 22mm or longer, usually longer than 25 mm
     
    6a(4b) a. Wings each with a very long cell just posterior to pterostigma, 3x or 4x the length of cells immediately proximal to it, thus with no crossveins immediately behind pterostigma or a single crossvein almost at its distal end Pachydiplax longipennis (Burmeister)
    6b a. Wings each with cells posterior to pterostigma no more than 2x length of adjacent cells, thus with 1 or more crossveins immediately behind pterostigma 7
     
    7a(6b) a. Vein M2 distinctly undulate or, if undulation slight, male with spines on outer angle of metafemur very short, stout, hooked proximally 8
    b. Posterior margin of pronotum smoothly convex, without median notch
    7b a. Vein M2 not undulate; male with spines on outer angle of metafemur slender, not hooked proximally 11
    b. Posterior margin of pronotum variable but often with distinct median notch
     
    8a(7a) a. Vein Cu1 in hindwing arising at posterior angle of triangle 9
    8b a. Vein Cu1 in hindwing arising from outer side of the triangle, clearly anterodistal to the posterior angle 11
     
    9a(8a) a. Forewings with one cell row between veins M4 and Mp1, or at most with single doubled cell Ladona julia (Uhler)
    b. Triangle almost always 2-celled
    9b a. Forewings with 2 or 3 cell rows between veins M4 and Mpl for distance of at least two cells 10
    b. Triangle usually at least 3-celled
     
    10a(9b) a. Sternum of Ab1 of male with paired ventral processes Plathemis lydia (Drury)
    b. Female with lateral margins of middle abdominal segments parallel and with lateral carinae of Ab9 well-developed
    c. Wings with wide, brown band at nodus
    10b a. Sternum of Ab1 of male without paired, ventral processes Libellula
    b. Female with lateral margins of middle abdominal segments tapering gradually posteriorly and with lateral carinae of Ab9 absent or very weakly developed
    c. Wings variably patterned
     
    11a(7b,8b) a. Forewing triangle with proximal side <2x long as anterior side Leucorrhinia
    b. Pterostigmata each short and thick, about twice as long as wide, at least in male
    c. Tergum of Ab4 without distinct lateral carinae
    d. Forewings each with veins M4 and Cu1 divergent to wing margin
    e. Face white
    11b a. Forewing triangle with proximal side more than twice as long as anterior side 12
    b. Pterostigmata each about 3x or more as long as wide
    c. Tergum of Ab4 with distinct lateral carinae
    d. Forewings each with veins M4 and Cu1 variable
    e. Face not white in most species
     
    12a(11b) a. Forewings each with 6-7 paranal cells before subtriangle Erythemis simplicicollis (Say)
    b. Meso- and metafemora each with distal 3-4 spines much longer than more proximal spines
    12b a. Forewings each with 5 paranal cells before subtriangle 13
    b. Meso- and metafemora each with spines subequal or gradually increasing in length distally
     
    13a(12b) a. Wings each with one crossvein immediately behind pterostigma Sympetrum
    b. Posteror margin of pronotum directed dorsally, with median notch deep and V-shaped
    c. Tergum of Ab3 with lateral carinae distinctly more weakly developed than that of Ab4
    13b a. Wings each usually with two or more crossveins behind pterostigma Erythrodiplax umbrata (Linnaeus)
    b. Posterior margin of pronotum directed posterodorsally, with median notch shallow and V-shaped or absent
    c. Tergum of Ab3 with lateral carinae usually about as well developed as that of Ab4
     

Mature Nymphs

    1a a. Eyes small, located anterolaterally and dorsally, usually projecting above the general surface of the epicranium 2
    b. In dorsal view, epicranium posterior to eyes at least twice as long as eyes, and with lateral margins nearly parallel behind eyes
    c. Abdomen relatively long and tapering
    d. Lateral spines of Ab8-9 <1/3 length of respective abdominal segments
    1b a. Eyes usually larger, located more laterally, not generally projecting above the general surface of the epicranium 4
    b. In dorsal view, epicranium posterior to eyes < 2x as long as eyes, and with lateral margins usually somewhat convergent posteriorly behind eyes
    c. Abdomen usually relatively short and blunt
    d. Lateral spines variable
     
    2a(1a) a. Margin of median lobe of prementum smooth, or with crenulations nearly imperceptible Libellula
    2b a. Margin of median lobe of prementum distinctly crenulate 3
     
    3a(2b) a. Ab8 without dorsal hook Plathemis lydia (Drury)
    3b a. Ab8 with a dorsal hook Ladona julia (Uhler)
     
    4a(1b) a. Paraprocts each strongly decurved at the tip Erythemis simplicicollis (Say)
    b. Abdomen without dorsal hooks
    4b a. Paraprocts not strongly decurved at the tip 5
    b. If paraprocts somewhat decurved, then dorsal hooks present on Ab4-8
     
    5a(4b) a. Dorsal hooks present on some abdominal segments 6
    5b a. Abdomen without dorsal hooks 11
     
    6a(5a) a. Dorsal hook present on Ab9 Perithemis tenera (Say)
    6b a. No dorsal hook present on Ab9 7
     
    7a(6b) a. Dorsal hook present on Ab8 8
    7b a. Dorsal hook absent on Ab8 9
     
    8a(7a) a. Epiproct nearly as long as the paraprocts Leucorrhinia (in part)
    also: Premental setae 15 or fewer; lateral spines of Ab8 each much shorter than the middorsal length of that segment
    8b a. Epiproct no more than 2/3x as long as the paraprocts Sympetrum (in part)
    also: Lateral spine of Ab9 < than 0.5x the lateral length of that segment, including the spine, and not extending beyond 0.5x the length of the paraprocts
     
    9a(7b) a. Dorsal hooks on Ab2-4 only, small in size Pantala
    b. Crenulations of the labial palps quite deep
    c. Lateral spines on Ab9 markedly longer than the middorsal length of that segment, but not extending beyond the tips of the paraprocts
    9b a. Dorsal hooks on Ab3-6 at least, variable in size 10
    b. Crenulations not unusually deep
    c. Lateral spines on Ab9 variable
     
    10a(5b) a. Lateral spines of Ab9 markedly longer than the middorsal length of that segment, reaching almost to level of tips of the paraprocts Celithemis
    10b a. Lateral spines of Ab9 shorter than the middorsal length of that segment, not approaching level of tips of the paraprocts Erythrodiplax umbrata (Linnaeus)
     
    11a(5b) a. Lateral spines of Ab9 longer than the middorsal length of that segment or, if about equal, then the epicranium with a drak ridge extending medially from the posteromedial margin of each eye 12
    11b a. Lateral spines of Ab9 not longer than the middorsal length of that segment 13
    b. Epicranium without a dark ridge extending medially from the posteromedial margin of each eye
     
    12a(11a) a. Lateral spines of Ab8 shorter than the middorsal length of Ab9 Pachydiplax longipennis (Burmeister)
    b. Dark ridge extending medially from the posteromedial margin of each eye
    c. Epiproct no more than 2/3x the length of the paraproct
    12b a. Lateral spines of Ab8 longer than the middorsal length of Ab9 Tramea
    c. No dark ridge extending medially from posteromedial margin of each eye
    c. Epiproct at least 0.75x the length of the paraproct
     
    13a(11b) a. Very small, total length of mature nymphs <11 mm Nannothemis bella (Uhler)
    b. Palpal setae 6
    13b a. Larger, mature nymphs >12 mm in total length 14
    b. Palpal setae usually more than 6
     
    14a(13b) a. Lateral spines on Ab8-9 each distinctly less 1/3x the length of the middorsal length of their respective segments Sympetrum (in part)
    also: Palpal setae 9 or more, premental setae 13 or more; abdomen not very abruptly of at apex, more or less tapered
    14b a. Lateral spines on Ab8-9 each at least 1/3x the length of the middorsal length of their respective segments 15
     
    15a(14b) a. Lateral spines of Ab9 about as long as that segment's middorsal length Leucorrhinia (in part)
    b. Abdomen with 3 conspicuous longitudinal dark ventral bands
    15b a. Lateral spines of Ab9 usually distinctly shorter than that segment's middorsal length Sympetrum (in part)
    b. Abdomen without 3 conspicuous longitudinal dark ventral bands
     

References

    Needham JG, Westfall MJ, May ML. 2010. 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.
    Tennessen KJ. 2006.
    Odonata, pp. 237-294, in An Introduction to the Aquatic Insects of North America, 4th Ed. Merritt RW, Cummins KW, Berg MB. (eds.). Kendell/ Hunt Publishing Company: Dubuque, Iowa, USA.
    Walker EM, Corbet JS. 1975. The Odonata of Canada and Alaska, Vol. 3. Universityof Toronto Press: Toronto, Ontario. xvi + 308.

Page last updated: February 19, 2017 (EB)