Rapids clubtail (Gomphus quadricolor) COSEWIC assessment and status report: chapter 3

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Species Information

Name and classification

Gomphus (Gomphus) quadricolor Walsh 1863, or Rapids Clubtail (Figure 1), is a member of the family Gomphidae, the clubtail dragonflies, and the order Odonata, the dragonflies and damselflies. The type species for this genus is the Eurasian G. vulgatissimus (Linnaeus 1758), and much of the controversy regarding the taxonomy of North American Gomphus s. lat. results from the continuing uncertainty about which species, if any, belong with G. vulgatissimus (Needham et al. 2000). Most authors treat G. quadricolor as belonging to the subgenus Gomphus (Leach 1815). However Carle (1986) placed this species and the 16 other North American Gomphus s. str. within a new subgenus Phanogomphus. G. alleni Howe 1922 is a synonym. Recent North American authors use the name “G. quadricolor”. No subspecies of G. quadricolor are recognized and the species is distinct.

Morphological description

Gomphus quadricolor is a small dragonfly, with a wing length of 25-27 mm (Needham et al. 2000). The face is light green with two transverse dark lines. The thorax has a contrasting colour-pattern of brownish-black and yellowish green stripes. The dorsal pale thoracic stripe has a small pale spot off its posterior end. The slender abdomen is black with mostly linear yellow spots on the top of the first seven segments and small lateral spots. It usually lacks dorsal spots on the last three abdominal segments, but will rarely have a small yellow dot on the 8^th or 10^th segments. The 7^th to 9^th abdominal segments are expanded slightly in males, less so in the females, with large yellow lateral spots on the sides of the 8^th and 9^th segments. The legs and claspers are all black.

The anterior hamule of the male’s secondary genitalia is sickle-shaped, terminating in a slender hook. The vulvar lamina of the female is short, less than 1/6 the length of the 9^th abdominal segment and V-notched to nearly its base. Illustrations of the diagnostic shape of the male and female genitalia are presented in Walker (1958).

Larvae (Figure 2) have a lanceolate abdomen with lateral spines on the sixth to ninth segments, vestigial dorsal hooks distinct only on the ninth and tenth segments, and well-developed tibial burrowing hooks (Walker 1932). G. quadricolor larvae are similar to but smaller than those of G. spicatus (Dusky Clubtail) and G. exilis (Lancet Clubtail).

Gomphus quadricolor may be confused with other small gomphids in its range, but they have a yellow dorsal stripe on the 9^th abdominal segment and/or differ in the shape of the genitalia. G. adelphus (Mustached Clubtail) and G. viridifrons (Green-faced Clubtail) are similar but the tip of the male’s anterior hamule is blunt and the female’s vulvar lamina is much longer (Catling and Brownell 2000). G. spicatus (Dusky Clubtail) and G. descriptus (Harpoon Clubtail) are slightly larger, have some yellow on their legs, and more extensive yellow abdominal markings.

Figure 1. Gomphus quadricolor (male) at Humber River, 2005.

Figure 2. Gomphus quadricolor male larva (Walker1932). Reproduced with permission of the Entomological Society of Canada.

Genetic description

Genetic studies have not been conducted in this species.