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Familiar Bluet



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Enallagma civile

Hagen, 1861


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


Identification

The front of the male's head is blue striped with a broad black bar. The top of the head is largely black except for two small pale postocular spots. The pronotum is largely black with patches of blue. The middorsal carina is nearly always black bordered by a wide middorsal stripe half the width of the mesepisterna. The antehumeral stripe is blue and no more than half the width of the middorsal stripe. The dark humeral stripe widens anteriorly and generally is only 2/3 as wide as the antehumeral stripe at that point. The rest of the thorax is pale to bright blue fading ventrally. The legs are pale with broad black stripes on their outer surfaces, but the distal portio ns of the tibiae and all the tarsi lack black stripes. The abdomen is bright blue dorsally marked with black, becoming pale ventrolaterally. Segment 1 is entirely blue except for the basal 1/3 to 1/2 which is black dorsally. A large, irregular black spot occupies the apical half of segment 2 dorsally and is confluent with an apical ring. A similar spot on segments 3-5 extends dorsally for as much as half the length of the segment. There is a dorsal stripe that extend 1/2 to 3/4 or more the length of segments 6-7. Segments 8-9 are entirely blue and segment 10 is black dorsally. The cerci are uniformly black with a pale distal tubercle extending beyond the lower arm of the appendage but that is clearly encompassed by the upper arm when viewed laterally. The cerci are approximately 3/4 the length of segment 10. The paraprocts are pale with dark tips that curve slightly upward. Females may be either blue or tan. The head and thorax are similarly marked to the male. The middorsal carina may have a full-length hairline stripe. The legs are like those of the male. The middorsal lobe of the pronotum lacks any distinct pits. The mesostigmal plates are divergent anteriorly with the anterolateral corners elevated. The abdomen is generally marked with more black than in the male. Segment 1 is almost entirely black dorsally with pale apical rings. There is a broad full-length black stripe dorsally on segment 2. Segments 3-6 each have a hastate black stripe running their entire length, or nearly so. Segment 7 is generally all black dorsally with only a pale apical and sometimes basal ring. A full-length black stripe runs from segments 8-10 dorsally. This stripe is occasionally constricted basally on segment 8 and apically on segments 9-10.

Size

Total length: 29-39 mm; abdomen: 22-34 mm; hindwing: 16-21 mm.

Similar Species

Segment 7 in male Azure (E. aspersum ) and Northern (E. cyathigerum ) Bluets is all, or nealy so, black. Atlantic Bluet (E. doubledayi ) is very similar and careful examination of the male caudal appendages and female mesostigmal plates will be required for accurate identification. Male Familiar Bluets are one of two species in our region with a distal tubercle on the cerci. The other, Tule Bluet (E. carunculatum ) has a tubercle that protrudes beyond the end of the cerci. This is our most widely distributed bluet, but it is often found flying with other species, so look carefully at populations of little blue damselflies.

Habitat

Ephemeral or permanent ponds and lakes. Also slow flowing streams, irregardless of salinity and vegetation.

Discussion

This widely distributed southern species has extended its range dramatically, to now extend from as far south as Colombia and Venezuela and north into southern Canada. It is only absent from the Pacific Northwest in the United States. It has entered California only in the last 80 years and more recently western Montana, British Columbia, Oregon, New York and southern Ontario. It was accidentally introduced into Oahu in 1936 and now occurs commonly on all of the major Hawaiian Islands. Its success is probably due in part to its ability to colonize temporary and newly created aquatic habitats. Prey of this species includes adult sweet potato whiteflies and other small flies and insects. One study included notes about a population observed at Sandpit Lake in Dallas Co., Texas, where "...hundreds were in copula, ovipositing on small plants just below the surface of the water." Another study looked at oviposition site selection of Familiar Bluet and found that although aggregations reduced the risk of interference and may even lower predation risk, oviposition efficiency was also reduced. The peak activity is from midmorning into the afternoon. Males spend more days at the water (62% ) than females (39%), but males mate on fewer of these days (14% ) than females (79% ) (Bick and Bick 1963). There is no courtship involved in mating which may last as long as 45 minutes, but usually is over in 20 minutes. Egg laying occurs in tandem, with the male letting go to guard at a nearby perch before becoming completely submerged. Eggs are deposited in algae, roots, leaves and upright stems at the surface of the water. Females usually remain submerged an average of 12 minutes, but lay eggs for more than an hour below the surface, descending backwards. Studied polymorphic head color patterns and found that the majority (73-86% ) of mature adult males lacked a postoccipital bar, while in the majority of females it was present. These females were split in having this postoccipital bar confluent (41-42% ) and non-confluent (50-52% ) with the postoccipital spots. One author found Familiar Bluet males hiding underwater in a laboratory aquarium after the room temperature was accidentally left at cool temperatures overnight. This was apparently an attempt to escape the cold temperature and may suggest how damselflies escape cold weather in nature.

Distribution

Throughout the U.S. and southern Canada except for Pacific Northwest south through Mexico to Colombia and Venezuela.