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.
- Baird, JM and ML May. 2003. Fights at the dinner table: agonistic behavior in Pachydiplax longipennis (Odonata: Libellulidae) at feeding sites. Journal of Insect Behavior 16:189-216.
- Baird, JM and ML May. 1997. Foraging behavior of Pachydiplax longipennis (Odonata: Libellulidae). Journal of Insect Behavior 10:655-678.
- Dunham, M. 1994. The effect of physical characters on foraging in Pachydiplax longipennis (Burmeister) (Anisoptera: Libellulidae). Odonatologica 23:55-62.
- Johnson, C. 1962. A study of territoriality and breeding behavior in Pachydiplax longipennis Burmeister (Odonata: Libellulidae). Southwestern Naturalist 7:191-197.
- MacKinnon, BI and ML May. 1994. Mating habitat choice and reproductive success of Pachydiplax longipennis (Burmeister) (Anisoptera: Libellulidae). Advances in Odonatology 6:59-77.
- Macklin, JM. 1963. Growth rate of Pachydiplax longipennis as influenced by environmental factors. Proc. N. Cent. Br. Ent. Soc. Amer. 18:138-139.
- May, ML and JM Baird. 2002. A comparison of foraging behavior in two “percher” dragonflies, Pachydiplax longipennis and Erythemis simplicicollis (Odonata: Libellulidae). Journal of Insect Behavior 15:765-778.
- McCauley, SJ. 2010. Body size and social dominance influence breeding dispersal in male Pachydiplax longipennis (Odonata). Ecological Entomology 35(3):377–385.
- Paulson, D. 2011. Dragonflies and Damselflies of the East . Princeton University Press,
- Penn, GH 1951. Seasonal variation in the adult size of Pachydiplax longipennis (Burmeister) (Odonata, Libellulidae). Annals of the Entomological Society of America 44:193-197.
- Robey, CW. 1975. Observations on breeding behavior in Pachydiplax longipennis (Odonata: Libellulidae). Psyche 82(1):89-96.
- Rosser, WG, N Von Ellenrieder, JA Louton. 2006. Dragonfly Genera of the New World: An Illustrated And Annotated Key to the Anisoptera. JHU Press.
- Sherman KJ. 1983. The adaptive significance of postcopulatory mate guarding in a dragonfly Pachydiplax longipennis. Animal Behaviour 31:1107-1115.
- Wellborn, GA and JV Robinson. 1986. Microhabitat selection as an antipredator strategy in the aquatic insect Pachydiplax longipennis Burmeister (Odonata: Libellulidae). Oecologia 71:185-189.
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