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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- Aquatic Insects of Michigan
Gomphidae (Clubtails) of Michigan - Identification
Introduction
Michigan's second largest family of dragonflies, 31 species in 10 genera have so far been recorded in our state. The taxonomic status of one speciose genus, Gomphus sensu lato, continues to be studied but evaluation of both morphological and molecular data of species from North American and Eurasia is providing a clear systemic picture. A recent work by Ware et al. (2016) supports elevating the previous subgenera Gomphurus, Hylogomphus, Phanogomphus,and Stenogomphurus as genera, and that Gomphus sensu stricto is limited to Eurasia. Erpetogomphus has not yet been recorded in Michigan, but a record from northcentral Indiana may make it possible that it can be encountered in the southernmost part of our state.
Although adults are referred to as "clubtails," as the abdomen is often enlarged posteriorly to resemble a club, gomphids could just as easily be called "burrowing dragonflies," in reference to the nymphal habit of burrowing into various substrates in lotic and lentic waters. The morphology of immatures - reduced antennae segments and strong fossorial legs, among other morphological adaptations - is ideally suited for concealing themselves in substrate and loose particulate debris. It's very interesting to watch live captured individuals, when released or put into a container filled with silt, sand or other debris, quickly use their legs to conceal themselves. Most are found in silt, sand or gravel in lakes and rivers, but one species - Hagenius brevistylus - has adapted itself to conceal itself by sprawling within leafy and woody debris in streams and lakes.
Taxonomic References: Needham et al. 2014, Tennessen 2007
Adults
| 1a | a. Basal subcostal crossvein present | Progomphus obscurus (Rambur) |
| b. One crossvein present in forewing subtriangle | ||
| 1b | a. Basal subcostal crossvein absent | 2 |
| b. No crossvein in forewing subtriangle | ||
| 2a(1b) | a. Triangles with a crossvein | Hagenius brevistylus Selys |
| b. Each triangle with a supplementary longitudinal vein (trigonal planate) arising from its distal side | ||
| c. Hind femora reaching a little beyond the base of Ab3 | ||
| d. Very large size, usually > 70 mm in length | ||
| 2b | a. Triangles without a crossvein | 3 |
| b.Without a trigonal planate arising from its distal side | ||
| c. Hind femora not reaching beyond middle of Ab2 | ||
| d. Generally < 70 mm in length | ||
| 3a(2b) | a. Hind wing with a semicircular anal loop typically of 3 cells | Ophiogomphus |
| b. Male epiproct with the 2 branches separated either by a mere slit with the apexes continguous, or by a U-shaped or V-shaped notch | ||
| c. Female vulvar lamina nearly as long as Ab9 sternum | ||
| 3b | a. Hind wing with anal loop absent, or of 1-2 weakly bordered cells | 4 |
| b. Male epiproct with more or less widely separated branches (except Erpetogomphus) | ||
| c. Female vulvar lamina usually < 0.5x as long as Ab9 sternum | ||
| 4a(3b) | Hind femur long, reaching the base of Ab3, and bearing 4-7 long ventral spines in addition to the usual short ones | Dromogomphus |
| 4b | Hind femur not extending beyond the middle of Ab2, and usually bearing only the usual numerous, short, ventral spines | 5 |
| 5a(4b) | a. Pterostigma of fore wing short and thick, at its widest about 2.0x long as wide | Erpetogomphus designatus Hagen |
| b. Hind wing with 5 paranal cells | ||
| c. Branches of male epiproct long, parallel in its full length, and strongly hooked upward | ||
| 5b | a. Pterostigma of fore wing usually more elongate, about 3x long as wide | 6 |
| b. Hind wing with4-5 paranal cells | ||
| c. Branches of male epiproct shorter and divergent | ||
| 6a(5b) | a. Pterostigma < 4.0x long as wide, > 2.0x wide as space behind its middle | Stylogomphus albistylus (Hagen in Selys) |
| b. Male epiproct with lateral edges subparallel, its 2 branches shorter than the median length of the appendage | ||
| c. Small, total length < 40 mm | ||
| also: Outer side of fore wing slightly angulated near middle; anteclypeus pale; Male cerci yellow or white, laterally angulate with apexes very slender and curved upward | ||
| 6b | a. Pterostigma rarely < 4.0x long as wide, and rarely < 2.0x wide as the space behind its middle | 7 |
| b. Male epiproct with lateral edges widely divergent, its 2 branches longer than the median length of the appendage | ||
| c. Larger, usually > 40 mm | ||
| 7a(6b) | a. Pale species, with a faint or absent stripe each side of pale middorsal carina of thorax, and thoracic side stripes much reduced | Arigomphus |
| b. Male with end hook of posterior hamules long and falciform | ||
| c. Abdomen usually constricted at Ab9 | ||
| d. Apexes of cerci usually convergent and very slender | ||
| 7b | a. Usually a darker species, with conspicuous dark stripes on thorax | 8 |
| b. Male posterior hamule often with a sharp shoulder, but the end hook is not so long or falciform | ||
| c. Abdomen usually not constricted at Ab9 | ||
| d. Cercal apexes variable, but not convergent or very slender | ||
| 8a(7b) | a. Top of frons 4.0x wide as long | Stylurus |
| b. Male cerci simple, horizontal, without angular processes and only rarely with the lateral margins angular | ||
| c. Branches of male epiproct diverging at about the same angle as the cerci, usually obscured in dorsal view | ||
| d. Anterior hamules vestigial, slender, unarmed and difficult to see, wheras the posterior hamules are usually upright or leaning forward | ||
| e. Anterior lamina of male flat, not projecting above the rim of the genital pocket | ||
| f. Female vulvar lamina very short, sometimes vestigial | ||
| 8b | a. Top of frons about 3.0x wide as long | Gomphus complex, 9 |
| b. Male cerci usually with sharply angular processes | ||
| c. Branches of male epiproct often diverge more strongly than cerci, thier apexes conspicuous in dorsal view | ||
| d. Anterior hamules of male not vestigial, always bearing at least 1 hook or spine, and posterior hamules upright or leaning backward | ||
| e. Male anterior lamina usually projecting above the rim of the genital pocket | ||
| f. Female vulvar lamina variable, often 0.5x long as Ab9 | ||
| 9a(8b) | a. Width of head about 0.8x the length of the metafemora, or less | Gomphurus Needham |
| b. Forewings each with the anterior side of the triangle shorter than the proximal side | ||
| c. Large species, hindwing usually 32mm or longer, with Ab8-10 strongly expanded | ||
| 9b | a. Width of head distinctly >0.8x the length of the metafemora, usually >0.9x that length | 10 |
| b. Forewings each with the anterior side of the tirangle longer than the proximal side | ||
| c. Smaller species, or if hindwings longer than 32mm, then Ab8-10 not strongly expanded | ||
| 10a(9b) | a. Middorsal length of Ab8 < than 0.75x that of Ab9 | Hylogomphus Needham, Westfall and May |
| b. Males with the outer apical edge of the anterior hamules denticulate | ||
| c. Females with subgenital plate more than 1/2 the length of Ab9 sternum, and divided for much less than 1/2 its length | ||
| 10b | a. Middorsal length of Ab8 < than 0.75x that of Ab9 | Phanogomphus Carle |
| b. Males with the outer apical edge of the anterior hamules spinose or hook-like | ||
| c. Females with subgenital plate not more than 1/3 the length of Ab9 sternum, and, if nearly 1/3 as long, then divided for more than 1/2 its length | ||
Mature Nymphs
| 1a | a. Mesocoxae closer together than procoxae | Progomphus obscurus (Rambur) |
| b. Antennal segment 4 elongate, 0.25x as long as segment 3 | ||
| 1b | a. Mesocoxae not closer together than procoxae | 2 |
| b. Antennal segment 4 vestigial or a small, rounded knob | ||
| 2a(1b) | a. Abdomen subcircular, body very flat | Hagenius brevistylus Selys |
| b. Head with paired tubercles behind eyes | ||
| 2b | a. Abdomen not so flat, more cylindrical | 3 |
| b. Head without paired tubercles behind eyes | ||
| 3a(2b) | a. Wing cases strongly divergent | 4 |
| b. Middorsal length of Ab8 and Ab9 about equal | ||
| Habitat: lotic | ||
| 3b | a. Wing cases parallel along back | 5 |
| b. Middorsal length of Ab9 clearly longer than Ab8 | ||
| 4a(3a) | Epiproct, cerci and paraprocts all subequal in length | Erpetogomphus designatus Hagen |
| 4b | Cerci distinctly shorter, at most 0.8x the length of the epiproct and paraprocts | Ophiogomphus |
| 5a(3b) | Flattened Ant3 nearly oval | Stylogomphus albistylus (Hagen in Selys) |
| Habitat: lotic | ||
| 5b | Cylindrical Ant3 > 4x times as long as wide | 6 |
| 6a(5b) | Ab9 with a long acute middorsal ridge ending in a long, sharp apical hook usually markedly darker than body base color, ridge raised in lateral view | Dromogomphus |
| 6b | Ab9 without such an acute, dark middorsal ridge bearing dorsal hook at apex, and usually not markedly raised in lateral view | 7 |
| 7a(6b) | Pro- and mesotibiae with burrowing hooks absent or obsolete | Stylurus |
| Habitat: mostly lotic | ||
| 7b | Pro- and mesotibiae with burrowing hooks at outer apical angle about as long as width of tarsus | 8 |
| 8a(7b) | Ab10 longer than wide | Arigomphus |
| 8b | Ab10 wider than long | Gomphus complex, 9 |
| 9a(8b) | a. Middorsal length of Ab9 at least 1/2 its basal width | Phanogomphus Carle |
| b. Middorsal length of Ab10 at least 2/3 its basal width | ||
| 9b | a. Middorsal length of Ab9 < than 1/2 its basal width | 10 |
| b. Middorsal length of Ab10 no more than 1/2 its basal width | ||
| 10a(9b) | a. Abdominal tergites covered in coarse cuticular granules | Gomphurus Needham |
| b. Dorsal hooks present on Ab8 | ||
| 10b | a. Abdominal tergites not covered in coarse cuticular granules | Hylogomphus Needham, Westfall and May |
| b. Dorsal hooks not present in Ab8 | ||
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.
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.
Ware JL, Pilgrim EM, May ML, Donnelly TW, Tennessen KJ. 2017. Phylogenetic relationships of North American Gomphidae and their close relatives. Systematic Entomology (in print).
Last updated: May 3, 2020 (EB)