These are relatively large dragonflies with the ladies having a lovely green coloration and the gents being blue with a green head. The general range of these dragonflies is the eastern 2/3rds of the USA, Bermuda and a few other islands, and southern Ontario, Canada.
These are often seen quietly waiting for an unsuspecting meal to happen by. They are not shy about grabbing almost anything, even other dragonflies, and the spines on their legs act as a trap to hold their prey.
Dragonflies do not come after people. If you hold one in your hand it may feel threatened and bite, but they are not aggressive toward people.
This picture was taken July 22,2012, at Skymount Pond in Marlborough Township Open Space area. Pennsylvania, USA.
For a nice little write up you can visit:
For a map of the range of these wonderful insects, see the link below: