Blue-spotted Hawkers are large dragonflies more often seen on the wing than resting. If you can get a good look at them while they are flying over still water, you can recognize them by the two distinct transverse stripes on the sides of the synthorax. Some of the Darners (Telephlebiidae) also have transverse stripes on their synthoraxes but do not usually fly over still water. I have sometimes seen, on partly cloudy days, Blue-spotted Hawkers hanging on fences, grass or trees.