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Aztec Dancer



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Argia nahuana

Calvert, 1902


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Argia
Species nahuana Calvert, 1902 [Argia]
Syn Argia saalasi Valle, 1942


Identification

The male's head is dark blue with large postocular spots broadly connected. The pale blue antehumeral stripe is nearly as wide as the black middorsal stripe and the dark humeral stripe is forked posteriorly at about half its length. There are 4 and 3 postquadrangular cells in the fore- and hindwings, respectively. The legs are pale blue with black stripes on the outer femoral and inner tibial surfaces. The tarsi are pale blue armed with black spurs. The abdomen is blue with a large black anteapical spot and a smaller dark spot below on segment 2. The apical fourth of segments 3-6 is black. Segment 7 is generally black dorsally with a blue middorsal streak of varying width and a blue basal ring. Segments 8-10 are blue with black ventrolateral spots on segments 8 and 9 that may be confluent with one another. The cerci are distinct, in dorsal view, with a prominent medially directed lobe. Laterally, these appendages are no more than 2/3 the length of the paraprocts, and an apical ventrally directed tooth is often visible. The coloration of the female is similar to the male, but is pale brown instead of blue. The middorsal carina is usually pale brown and the pale antehumeral stripe is nearly as wide as the dark middorsal stripe. The mesostigmal plates are recognizable because of the broad transverse expanse of each posterior lobe. Abdominal segments 3-6 bear a basal and apical black spot that generally are not confluent with one another. Segment 7 is similar to the male but with a smaller apical spot below. Segments 8 and 9 both have a black spot dorsolaterally that may extend the full-length of each segment. There is often an additional apical spot laterally on each of these segments. Segment 10 is pale.

Size

Total length: 28-35 mm; abdomen: 23-28 mm; hindwing: 18-23 mm.

Similar Species

The lateral black markings on the abdomen of Leonora's Dancer (A. leonorae) taper to a point (apearing like spear-tips dorsally), unlike Aztec Dancer. Variable (A. fumipennis) and Lavender Dancers (A. hinei) both have a complete, dark, ventrolateral stripe on segments 8-10 (Aztec Dancer lacks any ventrolateral markings on 10) and are largely violet. Springwater Dancer (A. plana) had dark markings anterolaterally on segments 5 and 6 and the postoccular spots are not broadly joined. Double-striped Bluet (Enallagma basidens) has a pale stripe dividing the dark humeral stripe

Habitat

Small, shallow, clear water streams, fully exposed to sunlight with only moderate marginal vegetation.

Discussion

Bick and Bick (1958) studied the Odonata at Cowan Creek, Marshall County, in southern Oklahoma. Aztec Dancer was by far the dominant species at this creek, where they observed and documented its egg laying behavior: "Male and female perched in full sunlight on a blade of grass six inches from the margin of the creek where the water was one inch deep...The abdomen of the female was bent at a sharp angle and its tip touched the plant one half inch below the water surface where eggs were apparently deposited. She probed for a few seconds with the tip of her abdomen, remained motionless for two and one half minutes, probed briefly and remained motionless for five minutes. The pair visited three more blades of grass where the female alternately probed and remained motionless but for only 30 seconds at each blade."

Distribution

Western U.S. from Oregon south to California and east to Texas and Oklahoma. Also south into Mexico.