The Blue Dasher is a dragonfly of the skimmer

Libellulidae

The skimmers or perchers and their relatives form the Libellulidae, the largest dragonfly family in the world. It is sometimes considered to contain the Corduliidae as the subfamily Corduliinae and the Macromiidae as the subfamily Macromiinae. Even if these are excluded , there still remains a...

 family. It is common and widely distributed in the United States.
Mature males develop a bluish-white pruinescence

Pruinescence

Pruinescence, or pruinosity, is a "bloom" caused by pigment on top of an insect's cuticle that covers up the underlying coloration, giving a dusty or frosted appearance. The pruinescence is commonly white to pale blue in color, but can also be gray, pink, purple, or red; these colors may be...

 on the back of the abdomen

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 and, in western individuals, on the thorax

Thorax

The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

. They display this pruinescence to other males as a threat while defending territories at the edge of the water.

Although the species name longipennis means "long wings", the wings are not particularly long. Females do, however, have a short abdomen that makes the wings look longer in comparison.