Widow Skimmer - Libellula luctuosa
Taken in my backyard. Skimmers belong to family Libellulidae, the largest dragonfly family in the world with over 1,000 species. Dragonflies have compound eyes with tens of thousands of facets giving them a nearly 360 degree view and excellent movement-sensing ability - apropos for aerial hunters of other insects. They are, however, completely harmless to humans neither biting nor stinging.
The fossil record for dragonflies goes back some 300 million years (Carboniferous Period) which was almost 100 million years before the appearance of the dinosaurs. Some of these ancient animals had wingspans of 70 cm (over two feet)! Here's a beautiful dragonfly fossil (Meganeura) from the Carboniferous.
They haven't changed much since then (obviously an effective body design and mode of life).