The most common Dragonfly here is my favorite: the gorgeous Blue Dasher Dragonfly. Often six or more will zip around the ponds and stream in the sunshine. Like Batman, they seek tall vantage points to survey their domains. Dragonflies eat a lot of mosquitoes and other insects, but they are not pollinators.
In the bottom photo, two dragonflies mate in what looks like a lovely heart shape. Actually, the male, who is on top, has grabbed the female by the neck. They fly around like that for awhile, then she bends forward and locks her tender bits with his second set of tender bits, where he has just moved some sperm. He works hard to dislodge the sperm of any of her other mates, and may guard her until she deposits her eggs in the water. Dragonflies and damselflies are the only insects that reproduce in this elaborate way.
Learn more about Blue Dasher Dragonflies from The Bug Lady.