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Turquoise Bluet



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Enallagma divagans

Selys, 1876


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Enallagma
Species divagans Selys, 1876 [Enallagma]


Identification

The male's head is blue in front crossed with a black stripe. The top is black with a pair of large, elongated, blue postocular spots that are narrowly separated by the occipital bar. The middorsal stripe and carina of the pterothorax are black and vary from 1/3 to 1/2 the width of the mesepisterna. The antehumeral stripe is blue and no more than half the width of the middorsal stripe. The black humeral stripe is approximately equal in width to the antehumeral stripe and abruptly narrowed posteriorly. The rest of the pterothorax is turquoise-blue becoming cream ventrally. There is an abbreviated stripe on the upper end of the interpleural suture and a dark spot on the metapleural fossa. The legs may be blue or tan with black stripes on the femora and tibiae. The tarsi are pale. The abdomen is largely black dorsally and bright blue laterally becoming paler ventrally. Segment 1 is black dorsally with only a pale apical ring. There is a full-length black dorsal stripe on segments 2-7 that expands subapically on each segment and a narrow blue basal ring on segments 3-7. Generally there is a small pale subapical spot present on segment 7. Segments 8-9 are largely blue. Segment 8 has a wide basal triangle dorsally and often along there is an obscure lateral spot on segment 9. The dorsum of segment 10 is largely black. The caudal appendages are black and each is approximately half the length of segment 10. The cerci are white medially with a prominent dorsobasal lobe, when viewed laterally. The paraprocts are widest basally and curve upwards. The female generally paler than the male. The head and thorax differ from the male in the following ways. The postocular spots are larger and the pale antehumeral stripe is general ly wider. The black humeral stripe is divided longitudinally by brown for its entire length, sometimes completely replacing the black. The middle lobe of the pronotum lacks distinct pits. The hind margin of the posterior prothoracic lobe bears a prominent, pale, median tubercle with long setae. The mesostigmal plates are more or less triangular with a distinct posteromedial tubercle. Abdominal segments 1-7 are as in the male, with the black dorsal stripes only slightly narrower. The black on the dorsum of segment 8 covers at least 2/3 of the basal length. Segment 9 is blue with a basal black spot or stripe that is emarginate medially and extends to half the length of the segment. Segment 10 is entirely blue, with at most, a basal black band.

Size

Total length: 26-36 mm; abdomen: 22-30 mm; hindwing: 17-22 mm.

Similar Species

Azure Bluet (E. aspersum ) has blue dorsally on abdominal segment 7. Dorsally, abdominal segment 8 in Stream Bluet (E. exsulans ) is black and Skimming Bluet (E. geminatum ) has a black stripe ventrolaterally on segments 8 and 9. Skimming Bluet also lacks a pale occipital bar.

Habitat

Shaded sluggish creeks and streams, sloughs or lakes.

Discussion

This species is restricted to the eastern part of our region. Male and female Turquoise Bluets rarely stray far from water. Their flight is deliberate and slow. One study recorded females submerged for up to 30 minutes while laying eggs. Another, looked at the coexistence of a Tennessee population of Turquoise and Slender Bluet (E. traviatum ) which revealed Turquoise Bluet larvae experienced significantly greater survival and biomass increase than their congener. Fecal pellet analyses showed considerable dietary overlap and little evidence of resource partitioning between the two species.

Distribution

Eastern U.S.; Florida to Maine west to Oklahoma and Texas.