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Blue Dasher



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Pachydiplax longipennis

Burmeister, 1839


Order Odonata
Suborder Anisoptera
Superfamily Libelluloidea
Family Libellulidae
Genus Pachydiplax
Species longipennis (Burmeister, 1839) [Libellula]


Identification

This rather distinctive species is found throughout our area. It has a white face and the top of the frons is metallic blue in mature individuals of both sexes. The eyes are brilliant blue or green in males and reddish-brown in females. The front of the thorax is brown with a thin pale carina medially and a wider pale stripe on either side. The sides are pale green with three full-length brown stripes. The wings are typically clear but may be flavescent and have a dark brown stripe on either side of the midbasal space in males. The legs a re black and heavily armed. The abdomen is black with a pair of pale yellow stripes dorsally, interrupted on segments 3-8 to appear as dashes. Segment 9 and the caudal appendages are black, while 10 is pale. The abdomen is considerably shorter than in females. Older males develop a pale pruinose blue color dorsally and more slowly laterally on the thorax and over the entire abdomen. Females become pruinose, but much more slowly than males.

Size

Total length: 28-45 mm; abdomen: 23-35 mm; hindwing: 30-43 mm.

Similar Species

Mature males resemble mature males of Eastern (Erythemis simplicicollis ) and Western (E. collocata ) Pondhawks, but they have an unmarked thorax. Females Seaside Dragonlets (Erythrodiplax berenice ) have a prominent ventrally projecting ovipositor. Species of tropical dashers (Micrathyria ) are similar, but all except Three-striped Dasher (M. didyma ) have lateral thoracic markings branched. All also have pronounced greenish spots dorsally on abdominal segment 7.

Habitat

Ponds, lakes, marshes, ditches, slow streams and other quiet bodies of water.

Discussion

This species is found around nearly any standing body of water where it is often the most common and abundant species. It is known from every county in Arkansas and every parish in Louisiana. As a result it ranks as one of the most well studied dragonflies in North America. The Blue Dasher is often seen perched vertically on twigs and branches at a variety of heights from just above ground level to tree tops with the wings depressed downward. On warmer days individuals will raise the abdomen in an obelisk position, reducing heat absorbance. They are aggressive predators, regularly taking over 10% of their body weight in prey daily. Adults roost in trees and are occasionally attracted to lights at night. This species will def end favored feeding sites for several days in a row. Breeding territories are established along the shoreline, where males will investigate all intruders, and defend and chase other males out by raising their pruinose blue abdomen. Multiple territories may be established in a single day. Mating takes place while in flight or perched and may last from 1/2 to 2 minutes. The male will guard the female from a nearby perch while she deposits eggs by flying low over the water and repeatedly tapping the abdomen to the surface, but never bobbing the entire body up and down. She may lay 300-700 eggs in only 35 seconds, usually in a heavily vegetated pond margin. Females remain farther back from the water when not laying eggs or mating. The tremendous variation in size within this species is generally correlated with larger individuals during the spring months and progressively smaller ones occurring in the summer and fall. One study found larvae of this species had a strong preference for the l eaf axil area of the aquatic plants they were associated with. This provides them protection and makes them less susceptible to fish predation. References: Baird and May (1997), Bick (1950, 1957), Byers (1930), Fried and May (1983), Frost (1971), Johnson (1962c), Mackinnon and May (1994), Mauffray (1997), May (1984), Needham (1946), Paulson (1966), Penn (1951), Robey (1975), Root (1924), Sherman (1983), Wellborn and Robinson (1987), Wright (1943b).

Distribution

Throughout southern Canada and U.S. except Great Basin; also Mexico, Bermuda, Bahamas and Belize.