The Blue Dasher (Pachydiplax longipennis) is a dragonfly of the skimmer family.

For instance, male Blue Dashers (Pachydiplax longipennis) assume an obelisk-like posture while guarding their territories or during conflicts with other males, displaying the blue pruinescence on their abdomens to best advantage.

In the Common Whitetail and Blue Dasher dragonflies (Plathemis lydia and Pachydiplax longipennis), males display the pruinescence on the back of the abdomen to other males as a territorial threat.