You've seen dragon flies. They are those huge blue or green (sometimes bronze or red) insects, flying in a zig zag pattern in the air, catching bugs on the wing.
The shorter stubbier ones are sometimes referred to as 'darners' for the flight pattern they follow, incessantly.
Did you know that the juvenile phase of this insect, the nymph, lives for several years underwater, without coming up for air?
They only start breathing when they crawl out of the water onto a reed, split open their back and the adult form, complete with crumpled wings, emerges.
The first time I ever saw this, I was astounded at the ugly blackish bug that crawled out of the water, and only when it had hatched out into a dragon fly did I realize what a miracle I had witnessed.
The nymphs live in the mud of a pond for up to three seasons, eating mosquito larvae and other tiny creatures.
As adults, they live only for the remainder of the summer, flying their patrol type pattern - the males in open spots like lawns, above roofs, and over roads or bodies of water, the females hanging around closely near a small pond or other place where she can lay her eggs.