Blue Skimmer Dragonfly (Libellula vibrans). Although sometimes scary looking, they are harmless to humans and an important component to healthy eco-systems. Dragonflies were some of the first winged insects to evolve over 300 million years ago. There are more than 5,000 specie of dragonflies. Dragonflies begin as aquatic larvae, spending up to two years in wetlands eating mosquitos, tadpoles, and other insect larvae. They are an important part of a healthy eco-system, and conservation of wetlands is important to their sustained survival.