After hatching, the nymphs stay in the water for three months to five years, depending on the species. Nymphs whole heartedly consume insects, worms, mollusks, fry, small fish, tadpoles, frogs, and more. Ponds with lots of nymphs rarely have fry that survive to adulthood. I saw one two inch nymph with a three inch frog clasped in its fierce jaws. If you wish to control these predators, you have to hand pick them out of the water.
Adults eat most flying insects including mosquitoes.
When a green darner shows up at my pond, it really stands out because it is one of the biggest and fastest dragonflies. They are smaller and have short, wide, blue bodies. To learn more about dragonflies, there is a dragonfly page based in Texas which shows real photos of the species present in that area. There is also a site with drawings of larval and adult dragonflies at this water bug site . A photo of one of my dragonflies is at the top of this page.