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Azure Bluet



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Enallagma aspersum

Hagen, 1861


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


Identification

The front of the head in the male is blue with a distinct black line above the clypeus. The top of the head is black except for thin pale occipital bar that is only narrowly separated from a pair of large blue, oval postocular spots. The pronotum is black dorsally with a pair of medial blue spots. The middorsal carina and stripe of the pterothorax are black with the latter approximately half the width of the mesepisterna. The blue antehumeral stripe extends no more than half the width of the middorsal stripe. The black humeral stripe narrows posteriorly, often expanding anteriorly to the mesepimeron, but generally remaining narrower than the antehumeral stripe. The rest of the pterothorax is pale blue, fading ventrally. The legs are pale with dark stripes laterally and the tarsi are typically black with pale tarsal claws. The abdomen is blue above, fading laterally and ventrally. Segment 1 is black in the basal 1/2 of the segment dorsally and there is a black spot on the apical 2/5 of segment 2 that is confluent with the apical ring. There is a narrow, dorsal black stripe that starts basally on segment 3 and extends the full-length of the segment widening distally. The entire dorsum of segments 4-6 is black except for a pale basal ring. Segment 7 is black on the basal forth of the segment and blue apically and laterally. Segments 8 and 9 are entirely blue. Segment 10 bears a wide dorsal black stripe th at narrows apically. The carci are dark and distinctly bifurcated when viewed laterally. The upper arm is much longer and more pronounced than the lower. The dark paraprocts curve dorsally to reach the lower arm of the appendages above. The head and thorax of the female are similar to the male but with the pale blue colors generally replaced by green. The postocular spots are significantly smaller than in the male. There are a pair of kidney-shaped pits on the posterior 1/3 of the pronotum. The mesostigmal plates have a distinct posterior border. The abdomen is generally paler than in the male and especially ventrolaterally. Segments 1 and 3-6 are generally similar to the male. Segment 7 is nearly all black with an apical blue ring. Segment 8 is black with narrow pale apical ring and a pair of pronounced blue spots on the basal 1/3 to 1/2 of the segment. Segments 9-10 are black dorsally with only a pale blue apical margin.

Size

Total length: 27-34 mm; abdomen: 21-27 mm; hindwing: 15-20.

Similar Species

Familiar (E. civile), Alkali (E. clausum), Atlantic (E. doubledayi ) and Boreal (E. boreale ) Bluets are all a paler blue dorsally than Azure Bluet. This species is restricted to the northeastern portion (eastern Oklahoma and northern Arkansas ) of our range. Skimming Bluet (E. geminatum ) has a black ventrolateral line on segments 8-10 and 10 is black laterally.

Habitat

Fishless lakes and semipermanent ponds and bogs.

Discussion

In Texas this species has only been reported from from Collin, Dallas and Wise counties in the north central portion of the state. It is generally restricted to fishless ponds and lakes, but has been reported occurring along shallow grassy or boggy shorelines. Unpaired males seldom perch or maintain a territory prior to mating. One study found females move away from the water between noon and 1:00 pm each day, only to reappear in numbers between 1:30 and 2:30 P.M. Males will often seize egg laying females from the water. Sperm transfer generally occurs while in tandem and perching on vegetation, quickly followed by mating lasting an average of 14 minutes. Females most often lay eggs completely submerged and unaccompanied. Unlike most damselflies, female Azure Bluets do not begin laying eggs above the water and back down, but rather she determines an appropriate stem and immediately proceeds down it, head first. The male separates upon contact with the water and perches nearby. One study reported a female submerge as low as 15 inches to lay eggs at the base of the plant, apparently as an adaptation to avoid summer drought. Egg laying generally lasts no more than 25 minutes. In Ontario, Canada, it was formerly restricted to bog-marginated lakes, but it seems to be expanding its habitat to include artificial ponds and calcareous and alkaline gravel pits.

Distribution

Eastern U.S. and southern Canada from Georgia north to Quebec; west to Wisconsin and south to Texas.