The morphology of insects enables the phenomenal success of this class of arthropods. The sheer quantity and diversity of its taxa are matched by a large variation of modifications in its body structure. The high rate of speciation, short generations, and long lineage have caused insects to evolve in many ways, resulting in very large variations in morphology. These modifications allow insects to occupy almost every ecological niche, use a staggering variety of food sources, and possess diverse lifestyles. Insect body sizes range from 0.3 mm in the case of mymarid wasps, which parasitise insect eggs, to the 30-cm wingspan of the American owlet moth Thysania agrippina (family Noctuidae).
Insects are by far the most successful group in the Arthropoda. They differ in significant ways from the other classes of Hexapoda, such as Protura, Collembola, and others), which are now considered by some authorities to be more basal than insects.
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.