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Plains Clubtail



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Gomphus externus

Hagen in Selys, 1858


Order Odonata
Suborder Anisoptera
Superfamily Gomphioidea
Family Gomphidae
Genus Gomphus
Species externus Hagen in Selys, 1858 [Gomphus]
Syn Gomphus consobrinus Walsh, 1863


Identification

This species is widely distributed throughout the region, but not as yet reported from Louisiana. Its face is pale yellowish and devoid of dark marks. Females have a stout spine at each end of the vertex. The thorax is pale yellowish-green and the dark brown middorsal stripe is widened slightly, to appear nearly parallel. This stripe is thinly divided by the pale middorsal carina. The antehumeral stripe is narrowly confluent with the humeral stripe at its upper end. There is a pale yellowish stripe, no more than half their width, between these two stripes. The mid- and third lateral stripes are present, well-developed and only narrowly confluent at their lower ends. The paler yellow stripe separates the two, but this may become obscured in older individuals. The legs are dark brown or black with a yellow stripe on the outer surface of the tibiae. The wings are clear with a brown pterostigma. The abdomen is black with interrupted pale middorsal and lateral stripes. Segments 7-9 are widely expanded with the middorsal stripe appearing as spearheads on segments 7-8. There is only a pale basal spot on segment 8 in females. Segment 9 has a broad yellow stripe dorsally and segment 10 is yellow. The male cerci are parallel, not divergent, when viewed dorsally.

Size

Total length: 52-60 mm; abdomen: 36-43 mm; hindwing: 30-35 mm.

Similar Species

This medium-sized robust yellowish species is most similar to Tamaulipan (G. gonzalezi ) and Pronghorn (G. grazlinellus ) Clubtails. Tamaulipan Clubtail is generally larger and darker with wider brown thoracic stripes and the females lack the erect yellow spines at each end of the postocellar ridge. Pronghorn Clubtail is smaller, but may not always be reliably separated from Plains Clubtail. The epiproct of male Pronghorn Clubtails is barely wider than the cerci. Sulphur-tipped Clubtails (G. militaris ) are smaller with yellow on the femora and more yellow on the club.

Habitat

Large muddy bottomed rivers and streams with moderate flow.

Discussion

Females fly low over streams tapping their abdomen to the water surface. Adults emerge late at night and early in the morning on vegetation, logs, and artificial structures only a few feet above the water. They generally perch on the ground or just above on low vegetation.

Distribution

Utah south to Texas.