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Vesper Bluet



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Enallagma vesperum

Calvert, 1919


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Enallagma
Species vesperum Calvert, 1919 [Enallagma]
Syn Enallagma laurenti Calvert, 1919


Identification

The face of the male is mostly yellow with bro wn eyes that become paler laterally. The top of the head is black with long postocular spots that are confluent with the occipital bar. The pronotum is largely pale. The middorsal thoracic carina is black. The black middorsal stripe is 1/4-1/3 the width of the mesepisterna. The antehumeral stripe is yellow-orange and 1-1.5 times the width of the middorsal stripe. The humeral stripe is black and largely reduced to a hairline. The rest of the pterothorax is orange or yellow. The legs are orange-yellow and occasionally bear a dark stripe on the femora. The abdomen is orange becoming yellow or blue-green laterally. Segment 1 nearly all black. Segment 2 has a dark stripe dorsally. Segments 3-8 are nearly all black except for narrow pale basal ring on each segment. Segment 9 dorsally and 10 laterally are blue. The cerci are subequal in length to segment 10. The paraprocts are half the length of the cerci and nearly straight in profile. The female is generally duller in color, more yellowish, than the male. The eyes are brown. The head and thorax are generally like the male, but without extensive black markings. There are distinct pits on the middle lobe of the pronotum. The mesostigmal plates are triangular with a well-defined posterior margin, strong medial ridge and a pale posteromedial tubercle. The pale areas of the abdomen are yellowish, sometimes blue-green. Segments 1-8 are like the male. Segment 9 has a black triangular spot dorsally. Segment 10 is pale dorsally.

Size

Total length: 29-37 mm; abdomen: 24-30 mm; hindwing: 15-21 mm.

Similar Species

Vesper Bluet is the only largely yellow bluet in our region. Females of Orange Bluet (E. signatum ) are similar, but the humeral stripe in Vesper Bluet is much narrower and the prothoracic pits in Orange Bluet are positioned more anteriorly. No forktail in our region is yellow with abdominal segments 9 and 10 blue.

Habitat

Most commonly found in heavily vegetated ponds and lakes, but occasionally in slow reaches of streams.

Discussion

Vesper Bluet is an unusual species in that it is most active in the late evening, as its name implies, and often does not appear over water until sunset. I have collected them at mercury vapor lights just after dusk. Their coloration and delicate shape allow them to easily take cover in vegetation during the day; however, they may be seen sneaking about in the morning hours as well. Pairs may leave the water, for up to 20 minutes, to mate. Egg laying occurs in tandem, occasionally after dark in stems and other vegetation lying just below the surface.

Distribution

Eastern U.S. from Florida north to Maine, west to Wisconsin and south to Texas.