Black-shouldered Spinyleg
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Dromogomphus spinosus
Selys, 1854
Order Odonata
Suborder Anisoptera
Superfamily Gomphioidea
Family Gomphidae
Genus Dromogomphus
Species spinosus Selys, 1854 [Dromogomphus]
Identification
Black-shouldered Spinyleg is distinctive from the other spinylegs in the region in having the antehumeral and humeral stripes fused for nearly their entire length. At most there is a thin pale green stripe between the two. The face is greenish and usually unmarked, but some individuals may have a dark cross-stripe. The top of the frons is green and the vertex is black, with a pair of distinct black spines, in the female. The midlateral stripe is generally reduced to a short stalk at its lower end. The third lateral stripe is reduced to thin line on the suture. The legs are black and the wings have a dark costa. The abdomen is mostly black with an interrupted greenish middorsal stripe. Segments 7-9 are dark brown to black and expanded laterally. The caudal appendages are black.
Size
Total length: 54-67 mm; abdomen: 42-45 mm; hindwing: 34-36 mm.
Similar Species
This is the only spinyleg and clubtail that has a broad dark shoulder stripe formed from the fusion of the dark antehumeral and humeral stripes.
Habitat
Small to large streams and oxbows with slow to rapid flow and sandy or muddy bottoms.
Discussion
This species has a distinctive egg laying behavior. Females fly quickly over the water, tapping the abdomen at regular intervals, depositing eggs. Pairs may stay in copula for some time high in trees. I have seen this species abundant, perched on the ground and bridge guardrails near streams. One study documented the invasion of this species into a Tennessee lake that resulted in a dietary shift in coexisting larval baskettails (Epitheca).
Distribution
Throughout eastern U.S. and southeastern Canada.
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