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The Blue Dasher (Pachydiplax longipennis) is one of the best known North American skimmers (family Libellulidae). It occurs from southern Canada south through Mexico and Belize, the Bahamas and Cuba (Rosser et al. 2006).
The males are easily recognized due to the yellow-striped thorax, metallic-green eyes, mostly white face, and pale blue abdomen, often with a dark tip. Females and immatures also have a yellow-striped thorax, but the abdomen has a longitudinal yellow and brown/black pattern. The eyes are reddish brown above and blue-grey below. Females have a short, blunt abdomen, while the abdomen of juveniles is longer and thinner and tapered at the posterior end. Older females may resemble worn males as their abdomen turns blue-grey and the eyes acquire a greenish tint (Paulson 2009).
The life history and behavior of blue dashers has been well studied (Baird & May 1997, 2003, Dunham 1994, Johnson 1962, MacKinnon & May 1994, Macklin 1963, May & Baird 2003, McCauley 2010, Penn 1951, Robey 1975, Sherman 1983, Wellborn & Robinson 1986). The larvae live in still waters like ponds, marshes, swamps, and ditches, as well as slow moving streams. Blue dasher females are elusive. They oviposit among vegetation, often accompanied by a guarding male. Copulation usually occurs in flight and lasts only for a few seconds. Blue dasher males are usually very conspicuous. They spend much of their time perched on aquatic vegetation or on shrubs and trees near the breeding habitat. The wings may be folded forward to cover the eyes. In mid-summer, they often assume the obelisk posture with the abdomen raised perpendicular to the ground. From time to time, a male will dash after small flying insects, soon returning to its perch to consume the prey. Males are territorial, aggressively engaging with intruders both at feeding and at breeding sites.