Gomphidae - Clubtails

Introduction

Michigan's second largest family of dragonflies, 31 species in 8 genera have so far been recorded in our state. The taxonomic status of one genus, Gomphus, continues to be disputed. 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. Larval morphology - 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.

Adults (adapted from Westfall and Tennessen 1996)

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
	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
	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

Mature Nymphs (adapted from Westfall and Tennessen 1996)

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	Epiproct, cerci and paraprocts all subequal in length	Erpetogomphus designatus Hagen in Selys
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

References

Westfall MJ, Tennessen KJ. 1996. Odonata, pp. 164-211 in An Introduction to the Aquatic Insects of North America, 3rd Ed. Merritt RW, Cummins KW (eds.) Kendell/ Hunt Publishing Company: Dubuque, Iowa.

Last updated: August 4, 2008 (EB)