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Rainbow Bluet



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Enallagma antennatum

Say, 1839


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Enallagma
Species antennatum (Say, 1839) [Agrion]


Identification

This is a beautiful species in which the males have a bright orange face, a prominent blue-green occipital bar and pair of narrowed postocular spots that may be confluent with the bar. The eyes are brown on top fading to green or yellow below. The middorsal stripe is black and half the width of the mesepisterna. The antehumeral stripe is orange to greenish-yellow and the rest of the thorax is largely pale blue-green fading extensively to yellow-green ventrally. The legs are yellowish-orange with black markings. Abdominal segments 1-7 are largely black dorsally. Segments 4-7 are green laterally and segments 1-3 and 8-10 are blue laterally. Segment 8 is entirely black dorsally, except for a narrow blue apical band. Segment 9 generally completely blue, with a narrow black basal band occasionally present. Segment 10 is black dorsally becoming blue or yellow laterally and ventrally. The deeply bifurcated cerci are black and not more than 2/3 the length of segment 10. The paraprocts are nearly all pale, becoming dark apically and curving dorsoanteriorly. The female is similarly colored and patterned to the male on the head and thorax, but the middorsal carina is generally paler. The mesostigmal plates are bordered posteriorly by a distinct sulcus, though a deep pit is lacking. The plates are more or less triangular with a pale tubercle at the posteromedial corners. Mesepisternal tubercles are lacking, but there is a transverse swelling medially behind each mesostigmal plate. The abdomen is marked as in the male on segments 1-6. Segments 7-9 are generally all black except for a narrow apical band and there is generally a median pale spot dorsally on segment 9. Segment 10 is black narrowing apically, but often not actually extending the length of the segment.

Size

Total length: 27-33 mm; abdomen: 21-27 mm; hindwing: 15-21 mm.

Similar Species

Because it is so colorful, Rainbow Bluet is more likely to be mistaken for a forktail (Ischnura ) in the field rather than another bluet. None of the forktails in the south-central United States, however, have an orange face and blue-green postocular spots like this distinctive bluet.

Habitat

Slow streams, lakes, gravel and borrow pits.

Discussion

This northern species ranges southward to Oklahoma. It is considered one of the most primitive of the bluets. It appears to be most closely related to Stream (E. exsulans ) and Turquoise Bluet (E. divagans). One author described its habitat as the quiet reaches of streams where current is slow and where dense vegetation is lacking. It has also been reported occurring in gravel pits. Females may submerge themselves when laying eggs.

Distribution

New York, Ontario and Quebec Canada west to Montana south to Oklahoma.