Dragonflies have slender, elongated abdomens, robust bodies, and 2 pairs of wings that are usually outstretched horizontally. The wings are membranous and elaborately veined. The hindwing is wider at the base than the forewing. The eyes are compound, large, adjoin each other, and nearly cover the head. The antennae are short. The six legs are poor for walking but good for perching.
Larvae (nymphs) are aquatic, usually drab, with 6 legs and with small wing buds. Gills are located inside the rectum (unlike those of damselflies, which extend from the hind end like 3 leaflike tails). They breathe by drawing water in and out of their hind end. By forcefully expelling this water, the animal can move quickly in a form of jet propulsion.
To distinguish between the many types of dragonflies, note the details of wing vein patterns as well as colors and markings on wings and body. Wing details, for example, can include coloration of the pterostigma, a narrow cell along the leading edge of the forewing, which is often black, white, and/or brown, and thickened. Males and females often have different colors and markings. Subadults often have different markings, too.