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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Arigomphus (Gomphidae) (Pond Clubtails) of Michigan - Identification

[under construction]

Three of the nine species of this North American genus of have been reliably recorded from Michigan, with an addition species - A. submedians - likely to encountered in the southwestern part of the Lower Peninsula. Unlike other Michigan species of Gomphidae, these dragonflies are more likely to be encountered in lentic (lakes and ponds) bodies of water.

(Taxonomic References: Needham et al. 2014, Tennessen 2019)

Adults

1a a. Tibiae entirely black 2
b. Male cerci each with a prominent, lateral, angular process
c. Subgenital plate with lobes each more or less symmetrically rounded, and somewhat divergent distally
1b a. Outer surface of tibiae yellow 3
b. Male cerci each without a prominent, lateral, angular process
c. Subgenital plate with lobes distinctly asymmetrical distally, inner margins nearly straight and outer margins convex, usually almost contiguous distally
 
2a(1a) a. Occiput about 0.5x as long as its greatest width, strongly convex, notched medially (viewed anteriorly) Arigomphus cornutus (Tough)
b. Male epiproct with branches very divergent, their span >1.5x width of Ab10
c. Male cerci with medial branches robust, their tips nearly contiguous
d. Female with large horn at each end of postocellar ridge
2b a. Occiput much less than 0.3x as long as its greatest width, weakly convex, not notched medially Arigomphus furcifer (Hagen)
b. Male epiproct with branches less divergent, their span only slightly greater than width of Ab10
c. Male cerci with medial branches very slender, their tips not nearly contiguous
d. Female without large horn at each end of postocellar ridge
 
3a(1b) a. Occipt with a sharp median elevation, sometimes with extreme apex slightly divided Arigomphus villosipes (Selys)
b. Posterior hamules of male with apical hook awl-like (evenly tapering to fine point) and lacking a keel (in lateral view)
3b a. Occiput without a sharp median elevation Arigomphus submedianus (Williamson)
b. Posterior hamules of male with apical hook widened by a distinct keel (in lateral view) along the dorsomedial margin
 

Mature Nymphs

1a a. Ab4-9 tergites with a medial, longitudinal cluster of short, stiff setae more closely grouped than adjacent, sparse, lateral fine setae, forming the appearance of a narrow, isolated, low middorsal ridge 2
b. Distal half of prementum with sides convergent to parallel
1b a. Ab4-9 tergites with medial setae clustered only slightly more than adjacent lateral setae, and thus not forming a semblance of a middorsal ridge 3
b. Distal half of prementum with sides divergent
 
2a(1a) a. Side of prementum usually parallel in distal 6/10, sometimes slightly convergent Arigomphus villosipes (Selys)
b. Ab9 posterolateral spine length <0.5 mm, ratio of spine length : Ab10 ventral length 0.19-0.23
c. Median process of ligula often bifid but variable
d. Ab8-9 without a middorsal hook
2b a. Side of prementum clearly convergent in distal 6/10 Arigomphus submedianus (Williamson)
b. Ab9 posterolateral spine length =>1.2 mm, ratio of spine length : Ab10 ventral length 0.60-0.74
c. Median process of ligula entire, tip acute
d. Ab8-9 usually with a small, flat middorsal hook
 
3a(1b) a. Ratio of ventral paraproct length : Ab10 length 0.55-0.63 Arigomphus cornutus (Tough)
b. Ratio of Ab10 length : width <1.35
c. Ratio of Ab9 length : width 1.01-1.23
3b a. Ratio of ventral paraproct length : Ab10 length 0.38-0.47 Arigomphus furcifer (Hagen)
b. Ratio of Ab10 length : width >1.35
c. Ratio of Ab9 length : width 1.23-1.62
 

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.

Page created: April 27, 2020 - Last updated:   May 3, 2020 (EB)