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Springwater Dancer



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Argia plana

Calvert, 1902


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Argia
Species plana Calvert, 1902 [Argia]
Syn Argia spegazzinii Nav¿¿s, 1934


Identification

The head of the male is blue, with a pair of postocular spots that are widely confluent with the compound eyes and separated by a pale occipital bar. The antehumeral stripe is pale blue bordered by a dark middorsal stripe of about the same width. The black humeral stripe is unforked and about half the width of the humeral stripe at its widest. It narrows considerably at its middle and then widens again at the upper end. The pterothorax becomes paler laterally. The metapleural suture is narrowly outlined by a black line. The legs are blue with heavy black markings on the outer femoral and inner tibial surfaces. The tarsi are black and armed with black spurs. There are generally 4 and 3 postquadrangular cells in the fore- and hindwings, respectively. The abdomen is bright blue with a small black basal spot dorsally and lateral spot apically on segment 1. The black basal spot and larger lateral apical spot on segment 2 may be connected to form a lateral stripe. Dark subb asal spot on segments 3-6 taper apically on the posterior segments. The dark apical spot on segments 3-6 are confluent medially. Segment 7 is nearly all black, except for a pale apical ring and middorsal line for half its length. Segments 8-10 are entirely pale blue. Laterally, there is a short ventrally directed apical black tooth on the cerci. The paraprocts are bifid with the superior lobe serrated and twice as long as inferior lobe. Individuals from western New Mexico are violet not blue. The female is pale brown with the head and thorax similar to the male. The mesostigmal plates are broadly flattened and unnotched but slightly angulate posteriorly and mesepisternal tubercles are present. The legs are much paler than in the male with only limited black markings on the femora and tibiae and the tarsi are brown. The abdominal color pattern closely approximates that of male, but with the black markings more extensive and the general pattern more variable. There is a basal black spot dorsolaterally on segment 9.

Size

Total length: 34-40 mm; abdomen: 26-33 mm; hindwing: 22-25 mm.

Similar Species

Aztec (A. nahuana ) and Variable (A. fumipennis ) Dancer both have a forked humeral stripe. Lavender (A. hinei ) and Variable Dancer both have a black ventrolateral stripe on abdominal segments 8-10 that is absent in Springwater Dancer. Apache Dancer (A. munda ) is larger, its legs are paler and the middorsal thoracic stripe is about the same width as the humeral stripe. Vivid Dancer (A. vivida ) is very similar and where these two species overlap, in the western part of our region, individuals should be checked carefully. There are no reliable field marks to separate these, but their ranges don't overlap extensively.

Habitat

Small shallow, canopied spring seepages with clay substrate.

Discussion

Violet forms of Springwater Dancer start appearing in western Texas, I have collected them in Brewster and Jeff Davis counties. A study of egg laying behavior of a population of this species at Cowen Creek in Marshall County, Oklahoma revealed pairs in which the female clasped a small dead twig and the male was supported by only the female. The female curved her abdomen slightly and deposited eggs on or in the clay of this spring at a depth of no more than half an inch. The pairs remained motionless for 15 minutes with little probing. A female was also seen laying eggs in clay outside of the spring itself. And another study of a p opulation in a southern Oklahoma stream found that males seized females predominately at the water's edge as females approached. Mating quickly occured at an average distance of 1.5 meters from the waters edge. Pairs did not change perch location, but were seen shifting positions on the perch during mating, 2-7 times. Mating and egg laying lasted an average of 27 and 47 minutes, respectively. Females were observed laying eggs almost exclusively in Nasturtium (water cress ) and debris.

Distribution

Central U.S. from Arkansas north to Wisconsin and west to Arizona; also south through Mexico to Guatemala.