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Western Forktail



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Ischnura perparva

Selys, 1876


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Ischnura
Species perparva Selys, 1876 [Ischnura]


Identification

The head and pterothorax of the male are blue-green with considerable black markings. The black humeral stripe is as much as three times as wide as the antehumeral stripe. The abdomen is mostly yellow-green dorsally with blue on segments 1-2, the base of 3, and all of 8-10. The dorsoapical prominence on segment 10 is forked and extends 1/3-1/2 again as high as the segment. The cerci gently curve downward, forming an acute process. The paraprocts are equally forked and project posteriorly. Females are orange becoming tan or olive with age and the thoracic pattern is often obscured. The head and thorax is like those of the male with the postoccipital spots becoming black dorsally older individuals. Only gynomorhpic females are known.

Size

Total length: 23-30 mm; abdomen: 18-24 mm; hindwing: 11-17 mm.

Similar Species

Male Western Forktails most closely resemble Mexican Forktail (I. demorsa ) but the dark ventrolateral stripe on segment 9 in that species is often reduced to less than half the length of the segment and in Western Forktail it is generally greater than 1/2. The postocularspots are much larger in Lilypad Forktail (I. kellicotti). Eastern Forktail (I. verticalis ) is similar and the dorsoapical projection in males is reduced considerably so that it appears absent in the hand.

Habitat

Ponds, lakes and slow moving streams with heavy vegetation and muddy substrate; often found in alkaline or saline situations.

Discussion

The range of this species barely extends into the south-central United States where it is known from a few scattered counties in New Mexico and also from Oklahoma with no additional information. It is common west of the Rocky Mountains. Females generally lay eggs in tandem, but may do so unaccompanied by the male.

Distribution

Northwestern U.S. and British Columbia south to Arizona, New Mexico and Oklahoma.