The subphylum Hexapoda (from the Greek for six legs) constitutes the largest (in terms of number of species) grouping of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura (all of these were once considered insects). The Collembola (or springtails) are very abundant in terrestrial environments. Hexapods are named for their most distinctive feature: a consolidated thorax with three pairs of legs. Most other arthropods have more than three pairs of legs.
A dragonfly is an insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera (from Greek ανισος anisos, "uneven" + πτερος pteros, "wings", because the hindwing is broader than the forewing). It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body. Dragonflies can sometimes be mistaken for damselflies, which are morphologically similar; however, adults can be differentiated by the fact that the wings of most dragonflies are held away from, and perpendicular to, the body when at rest. Dragonflies possess six legs (like any other insect), but most of them cannot walk well. Dragonflies are among the fastest flying insects in the world.
Dragonflies are important predators that eat mosquitoes, and other small insects like flies, bees, ants, wasps, and very rarely butterflies. They are usually found around marshes, lakes, ponds, streams, and wetlands because their larvae, known as "nymphs", are aquatic. Some 5680 different species of dragonflies are known in the world today.
Though dragonflies are predators, they themselves are subject to predation by birds, lizards, frogs, spiders, fish, water bugs, and even other large dragonflies.