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Pacific Forktail



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Ischnura cervula

Selys, 1876


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


Identification

The male's face is yellow-green. The top of the head is largely black except for two small blue postocular spots. The front of the thorax is black with a pale blue antehumeral stripe divided into small anterior and posterior spots. The sides of the thorax are pale blue. The pale areas on abdominal segments 1-2 and 10 are blue-green, segments 3-7 are yellowish green and segments 8-9 are blue. The anterior 3/4 of segment 1 is black dorsally. Segments 2-7 are black with pale basal ring on 4-7 and an additional apical ring on 7. Segment 8 is dark dorsally for as much as a fifth of the segment length. The lateral stripes on segment 8 extend 1/2 to 2/3 of segment length basally and half way on segments 9 and 10. The dorsoapical prominence on segment 10 is distinctly forked and extends 1/2 as high as the remainder of the segment. Females have a distinct tongue-like flange on the posterior margin of the pronotum. There is a distinct tuft of setae on each side of the median lobe. A vulvar spine is generally absent. The andromorphic form is uncommon, but like the male with the anterior mesepisternal spot larger and sometimes elongated as in Fragile Forktail (I. posita). The postocular spots may be narrowly confluent. The abdomen is generally like the male with segment 8 blue bearing lateral stripes, but lacking a basal ring. Segments 9-10 are generally black dorsally, but 9 may be partly or entirely blue. Gynomorhphic females are pale orang. A pale occipital bar is present and confluent with the postocular spots that are large and subtriangular in shape. The pterothorax is black with a middorsal stripe that is generally a third as wide as the mesepisterna. The antehumeral stripe is orange-tan and the humeral stripe is reduced and nearly absent. The abdomen is pale orange or tan. Segments 1-7 are generally patterned like the male. Segment 8 is blue with a short lateral stripe. Segment 9 is entirely black dorsally or with blue on the apical 2/3 and segment 10 is nearly all black.

Size

Total length: 24-31 mm; abdomen: 19-26 mm; hindwing: 13-19 mm.

Similar Species

Male Plains Forktails (I. damula ) have the pale antehumeral stripe reduced to an anterior and posterior spot like Pacific Forktail. The dorsoapical projection on abdominal segment 10 does not reach as high above the segment in Plains Forktail as it does in Pacific Forktail. The posterior margin of the the mesotigmal plate in males is black in Pacific Forktail and pale in Plains Forktail. Separting females where these two species overlap may require close in-hand examination. The entire front of the thorax is black in male Black-fronted Forktails (I. denticollis).

Habitat

Saline and alkaline ponds as well as slow-moving streams.

Discussion

Within our region this species is restricted to western New Mexico.

Distribution

Alberta Canada and Pacific Northwest south to New Mexico and Baja California.