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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Epitheca (Baskettails) of Michigan - Identification

Introduction

These are medium-sized (subgenus Tetragoneuria) to large (subgenus Epicordulia) dragonflies with dark brown bodies and small yellow, orange or reddish markings on the sides of the abdomen. Nymphs have prominent depressed, rounded abdomens and prominent middorsal hooks and lateral spines. Closeness of certain species may be the result of recent radiation of populations not being entirely isolated, resulting in hybridization between some species (Tennessen 2019).  E. cynosura, E. spinigera and E. princeps are distributed throught Michigan. E. canis is absent from the southwest of the Lower Peninsula, whereas E. costalis is restricted to the southeast portion of the Lower Peninsula (Lake St. Clair south to Lake Erie).

Taxonomic References: Needham et al. 2014, Paulson 2011, Tennessen 2019

Adults

    1a a. Both fore- and hindwings normally with distinct brown spots at nodus and apex as well as base Epitheca (Epicordulia) princeps Hagen
    b. Hindwings usually at least 38 mm in length
    1b a. Wings without nodal and apical brown spots, at most with a large basal spot on hindwing and a trace of brown at base of forewing Tetragoneuria, 2
    b. Hingwings usually < 35 mm in length
     
    2a(1b) a. Postfrons with a well-defined T-shaped brown spot Epitheca (Tetragoneuria) spinigera (Selys)
    b. Cerci of male with ventrobasal spine (rarely absent or reduced) and with apices directed posteriorly
    c. Cerci of female at least 3.0 mm long, longer than subgenital plate
    2b a. Postfrons without T-shaped brown spot (markings corresponding to base and stem may be present 3
    b. Cerci of male either without ventrobasal spine, or with apices directed posteroventrally
    c. Cerci of female usually < 3.00 mm long, usually shorter than subgenital plate (except some E. costalis)
     
    3a(2b) a. Male cerci with apices directed posteroventrally and with dorsal and ventrobasal spines Epitheca (Tetragoneuria) canis (McLachlan)
    b. Subgenital plate of female not extending beyond apex of sternum of Ab9, and with medial margin of each lobe convex or straight in apical half
    c. Mature females usually with most of wing membrane translucent brown
    3b a. Male cerci without a ventrobasal spine, usually directed posteriorly and without a dorsal spine 4
    c. Subgenital plate of female usually extending well beyond apex of sternum of Ab9 and with the medial margin concave in apical half
    c. Mature females usually with wing membrane darker brown
     
    4a(3b) a. Male cerci usually >3.1 mm long, each with inferior angle an acutely rounded, ventromedially projecting protuberance Epitheca (Tetragoneuria) costalis (Selys)
    b. Male Ab3 in ventral view usually markedly constricted in apical half
    c. Female cerci usually > 2.2 mm long
    d. Female sometimes with brown stripe along costal edge of each wing
    4b a. Male cerci usually < 3.1 mm long, each with inferior angle obtuse, not protuberant Epitheca (Tetragoneuria) cynosura (Say)
    b. Male Ab3 not markedly constricted in apical half
    c. Female cerci usually < 2.1 mm
    d. Female without a brown stripe along the costal edge of each wing
     

Mature Nymphs

    1a a. Prementum with only 3-4 primary setae, and many small but conspicuous stout stiff setae on ental surface Epitheca (Epicordulia) princepsHagen
    b. Ratio of prementum distal width : length > 1.6
    c. Palpal setae 4-5, none based in proximal third of lobe
    1b a. Prementum with 6-9 primary setae, but few if any stout setae on ental setae Tetragoneuria, 2
    b. Raio of prementum distal width : length < 1.3
    c. Palpal setae 5-8, with at least 2 in the basal third of lobe near the hinge
     
    2a(1b) a. Ab9 posterolateral spines relatively short, their tips extending at most to level of the tips of the paraprocts Epitheca (Tetragoneuria) canis (McLachlan)
    b. Ratio of Ab8 posterolateral spines length : Ab9 posterolateral spine length 0.36-0.48
    c. Maximum abdominal width => 8.5 mm
    2b a. Ab9 poasterolateral spines relatively long, their tips extending beyond level of the tips of the paraprocts 3
    b. Ratio of Ab8 posterolateral spines length : Ab9 posterolateral spine length 0.12-0.32
    c. Maximum abdominal width usually < 8.5 mm (E. spinigera may be greater)
     
    3a(2b) a. Central axis of Ab6 middorsal hook (lateral view) parallel or nearly parallel with horizontal axis of abdomen Epitheca (Tetragoneuria) costalis (Selys)
    b. Ab7-8 middorsal hooks low
    c. Ab9 posterolateral spine length 1.35-3.10 mm, ratio of spine length : distance between spine bases 0.54-1.04
    3b a. Central axis of Ab6 middorsal hook (lateral view) usually inclined relative to horizontal axis of abdomen 4
    b. Ab7-8 middorsal hooks raised
    c. Ab9 posterolateral spine length 1.10-2.60 mm, ratio of spine length : distance between spine bases 0.40-0.78
     
    4a(3a) a. Total number of palpal + premental setae usually 36 or more Epitheca (Tetragoneuria) spinigera (Selys)
    b. Metathoracic femur length 7.0-8.3 mm
    c. Abdominal width usually 8.2-9.9 mm
    d. Distance between bases of Ab9 posterolateral spines 3.00-3.60 mm (usually > 3.10 mm)
    e. Epiproct length 1.43-1.75 mm
    4b a. Total number of palpal + premental setae usually 35 or less Epitheca (Tetragoneuria) cynosura (Say)
    b. Metathoracic femur length 5.65-7.0 mm
    c. Abdominal width 6.6-7.9 mm
    d. Distance between bases of Ab9 posterolateral spines 2.50-3.30 mm (usually < 3.00 mm)
    e. Epiproct length 1.05-1.35 mm
     

References

    Needham JG, Westfall MJ, May ML. 2014. 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.
    Paulson D. 2011.
    Dragonflies and damselflies of the East. Princeton Field Guides. Princeton University Press, Pinceton, New Jersey, USA. 538 p.
    Tennessen KJ. 2019.
    Dragonfly nymphs of North America: An Identification Guide. Springer International Publishing, Cham, Switzerland: xiv + 620 p.

Last updated: April 27, 2020 (EB)