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Furtive Forktail



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Ischnura prognata

Hagen, 1861


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


Identification

Males are metallic black with only a thin green antehumeral stripe and pale blue on abdominal segment 9 and laterally on 10. The pterostigma in the forewing is twice the size as in the hindwing and transparent in its outer half. The dorsoapical projection on segment 10 is forked apically and readily visible in the hand. The cerci of the male are sharply forked with the upper branch projecting posteriorly and the lower ventrally. The paraproct s are stout and subequal to the upper branch of the cerci. Only gynomorphic females are known. Young forms have an orange-red thorax only interrupted by a black middorsal stripe. The abdomen is orange to segment 4, but becomes black apically. Older females become less vibrant and almost brown. There is no vulvar spine on segment 8. The posterior margin of the pronotum has a distinct v-shaped emargination at its middle. The mesostigmal plates are subtriangular and have small tufts of hair at their posteromedial corners.

Size

Total length: 30-37 mm; abdomen: 24-31 mm; hindwing: 14-20 mm.

Similar Species

Male and andromorphic female Rambur's Forktails (I. ramburii ) both have the top of abdominal segment 8 blue instead of 9. Only abdominal segments 1-2 are pale in the orange-red and olive-green form females. Segments 1-4 are pale in Furtive Forktail (I. prognata ) females.

Habitat

Heavily shaded ponds, swamps and sloughs.

Discussion

This eastern species is uncommon throughout its range and apparently finds its westernmost limit in the Sam Houston National Forest of east Texas. It has the longest abdomen of the forktails in the south-central United States. This species shares a behavioral similarity to many tropical damselflies in that it will fly ghost-like from one stem to another in the shady forest undergrowth, foraging at a height of 2 m or more.

Distribution

Eastern U.S. from Florida to New York southwest to Texas.