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Alkali Bluet



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Enallagma clausum

Morse, 1895


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Enallagma
Species clausum Morse, 1895 [Enallagma]


Identification

The male has a blue face. The top of the head is black with a pale occipital bar and postocular spots. The middorsal thoracic carina is blue surrounded by a black middorsal stripe half the width of the mesepisterna. The antehumeral stripe is blue and B= or less the width of the middorsal stripe. The black humeral stripe is narrower than the antehumeral stripe for most of its length. The rest of the pterothorax is blue becoming pale ventrally. The legs are blue or tan with black stripes on the femora and ti biae. The abdomen is primarily blue dorsally. Segment 1 is black in the basal half. Segment 2 has a black spot on its apical third and segments 3-5 have a spot on the apical forth of each segment. Segment 7 is largely black dorsally. Segments 8-9 are blue and segment 10 is black dorsally. The cerci are black, slightly upturned, and a third the length of segment 10. The paraprocts are just longer than cerci and upturned apically. The female is tan or blue with the head and thorax similar to the male. The middorsal carina is generally pale. The humeral stripe is narrower than in the male and often appears only as a hairline in the middle third. The middle lobe of the pronotum has a pair of distinctive pits. The mesostigmal plates are elongate with a pinched middorsal carina at the base. Abdominal segment 1 like is as in the male. Segment 2 may be entirely black dorsally or limited to single spot on its apical half. Segments 3-6 each have a hastate black stripe extending from B> or more t he length of the segment. Segment 8 is blue and segments 9 and 10 are black dorsally.

Size

Total length: 28-35 mm; abdomen: 22-28 mm; hindwing: 16-23 mm

Similar Species

Northern (E. cyathigerum ) and Boreal (E. boreale ) Bluets are very similar may be found flying with Alkali Bluet. Male Northern Bluet's have black on segment 2 expanded on to the sides. The black abdominal bands on the Boreal Bluet are truncate, not spear-shaped. Male Familiar (E. civile ) and Tule (E. carrunculatum ) Bluets have a distal tubercle on the cerci. Careful examination of the female mesostigmal plates will often be required to accurately identify females.

Habitat

Ponds and lakes, especially those with saline or alkaline water.

Discussion

Alkali Bluet gets its name because it is often the only damselfly inhabiting saline or alkaline lakes. It is not restricted to these bodies of water however and may be found on freshwater lakes.

Distribution

Northern plains and Great Basin from Quebec to British Columbia south to New Mexico and Texas.