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Black-fronted Forktail



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Ischnura denticollis

Burmeister, 1839


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Ischnura
Species denticollis (Burmeister, 1839) [Agrion]


Identification

The males has a solid metallic blue-black thorax with the antehumeral stripe entirely absent. The abdomen is dark dorsally with a blue-green metallic luster. Segment 8-9 are blue dorsally, the former with a narrow dark basal ring. The dorsoapical prominence on segment 10 is distinct but barely reaches above the height of segment 9, if at all. The tips of the cerci are directed anteroventrally. The upper arms of the forked paraprocts are slightly denticulate at their upper end. The lower arms project nearly straight posteriorly. The females are one of only two species in the south-central United States with a distinct nipple-like processes immediately posterior to the deep pit on each side of the pronotum. The andromorphic form is rare and differs from the male in the occasional presence of an antehumeral stripe and blue spot dorsally on segment 10. The gynomorhpic forms vary from pale blue to orang e with postocular spots larger than in the male and separated by a pale occipital bar. The abdomen is patterned as in the andromorphic form.

Size

Total length: 22-26 mm; abdomen: 17-21 mm; hindwing: 11-15 mm.

Similar Species

Black-fronted Forktail (I. denticollis ) is the only forktail in the region with the front of the thorax all black and completely lacking a pale antehumeral stripe.

Habitat

Vegetated streams or ponds, often associated with springs, especially at northern latitudes.

Discussion

Discussion. Black-fronted Forktail is more widely distributed than the other western forktail species. This species is in great abundance in Utah, in most aquatic habitats between 1,400 and 2,500 m where there is sufficient vegetation and a high enough minimum temperature to support damselflies. One author described Black-fronted Forktail as "undoubtedly the feeblest of all western Odonata..." In a Mexican population, survivorship for both sexes was among the lowest rates in the Odonata and that their ability to disperse is low. Unlike most forktails, females will lay eggs in tandem, usually in emergent grasses or debris. The average mating time is 20 minutes, the shortest of any forktail reported. O ne study on seasonal variation and morphometric differentiation in sympatric populations of Black-fronted Forktail with the more western San Francisco Forktail (I. gemina (Kennedy) ) found that hybridization does occur, but that the evidence shows hybrid unfitness.

Distribution

Western U.S. east to Oklahoma and Texas; also south through Mexico to Guatemala.