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Powdered Dancer



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Argia moesta

Hagen, 1861


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Argia
Species moesta (Hagen, 1861) [Agrion]


Identification

The head of young males is dark brown, with a pale labium, labrum, clypeus, genae and frons. Older individuals have a blue-white pruinosity dorsally on the head. There is a dark brown middorsal stripe and a pale antehumeral stripe approximately half its width. A dark narrow humeral stripe extends nearly to the antealar carina and is confluent with the mesepimeral stripe anteriorly. The legs are pale with dark stripes on the outer surfaces of the femora and the tarsi are black. The pterothorax, coxae and femora are all pruinose in older individuals. There are 4 and 5 postquadrangular cells in the fore- and hindwings, respectively. The abdomen is brown basally and distally on segments 9 and 10. The middle segments are much darker, almost black an d segments 1-6 are tan laterally. The abdomen in older individuals becomes black, except for pale areas laterally on segment 1 and the basal rings on segments 3-7. The cerci, when viewed laterally are blunt and rounded with a dorsally-directed tooth near apex. Females are similarly patterned to males and can be tan or blue. The narrow middorsal carina is outlined in black and a dark humeral stripe is barely visible. The metapleural suture is unmarked or often with a thin dark line and a brown spot in close proximity to the antealar carina. The mesostigmal plates have a distinct posterior lobe bearing a low ridge that curves over the middle half of each plate, when viewed dorsally. Mesepisternal tubercles are present. The legs are pale, but with dark stripes on the outer surfaces of the femora and the inner surfaces of the tibiae. The tarsi and accompanying spurs are dark. The abdomen is pale blue or brown basally becoming darker posteriorly and a pale stripe runs its full-length middor sally, but is constricted apically at each segment. There is a wide dark brown longitudinal stripe paralleling the middorsal stripe except for pale basal rings. Ventrolaterally, a brown spot is visible at the apex of segments 2-7. Segments 8-10 are pale with a dorsolateral dark stripe on segments 8 and 9.

Size

Total length: 37-42 mm; abdomen: 28-37 mm; hindwing: 22-29 mm.

Similar Species

Sooty Dancer (A. lugens ) is a larger and darker species with a dark stripe on each side of the middorsal thoracic stripe. Older males are also nearly black, lacking the white pruinescence seen in Powdered Dancer. The top of the middle abdominal segments in Tonto Dancer (A. tonto ) are blue or violet. Female Blue-fronted Dancers (A. apicalis ) are very simialar, but smaller and the last few abdominal segments are generally darker.

Habitat

Swift currents of rivers and lakes with emergent stones and rocky shores.

Discussion

Females in the southeastern United States may have more extensive black markings on the thorax and abdomen, such that they appear more similar to males. They have a wide middorsal stripe that is sometimes divided on each side by a thin pale stripe. The humeral stripe may also be wide and forked medially. A study of individuals in an Ohio stream revealed that individuals will move as much as 185 m away from the stream. Females spend the majority of their time 75-150 m from the water. Males become pruinose starting middorsally on the thorax and become sexually mature when this pruinescence reaches beyond the black midfrontal stripe and females aren't receptive to males until they become blue. This color change requires two days after maturation. Next to Dusky Dancer (A. translata), Powdered Dancer is probably the most widely distributed species in the genus, occurring from about 45o0 N latitude in Canada to about 20o0 N in Mexico. Powdered Dancer is adaptable when invading new areas, by laying eggs in the previously unutilized surface of Salix roots. Mating and egg laying average 22 and 47 minutes, respectively and females turn dark while in tandem. Tandem pairs will aggregate in large numbers to lay eggs in roots, stems, debris and algae, often submerging themselves more than a meter for periods up to an hour. Two additional studies have shown the first symphoretic association of Powdered Dancer with a non-biting midge (Nanocladius branchicolus ) and the effect of individuals losing their caudal lamellae swimming speed. If two of these lamellae are missing, larger individuals swim faster than smaller ones, but statistically slower than individuals that retain two or three lamellae.

Distribution

Throughout southern Canada and the United States, except for the Pacific Northwest. Also south into Mexico.