The abdomen always has ten segments. Segments 1 and 2 appear to be integrated into the thorax and are sometimes difficult to tell from the thorax. To find a particular segment, it is usually best to start with segment 10, far out at the tip, and count backwards. Because of its segmented nature, the abdomen is very flexible and is able to arch up or down (but not side to side). Learn to count abdomen segments as many of our descriptions are based on them.
The thorax is the centre for locomotion. It is a muscular powerhouse, controlling head, wing and leg movements. Dragonflies are unusual in their wing movements. Most insects’ wings are attached to plates of the chitinous exoskeleton that are, in turn, attached to muscles that move the plates that move the wings. Dragonfly wings, on the other hand, are directly connected to large muscles within the thorax. The interior of the thoracic exoskeleton is massively braced and strengthened to withstand the pressures of these large flight muscles. This bracing can be seen through the exoskeletons of lightly-pigmented individuals such as the Wandering Glider, the Four-spotted Skimmer and the Common Green Darner.
Their two short bristly antennae are thought to function as windsocks or anemometers, measuring wind direction and speed, thereby giving them a method with which to assess their flight. By the way, dragonflies have no sense of hearing, cannot smell and are unable to vocalize.
The face is a conglomeration of plates separated by seams called sutures. The sutures are often darkened into stripes. The upper half of the face is the frons, and the upper surface of the frons is a shelf-like protuberance on which various diagnostic markings may be found. The compound eye is composed of nearly 30,000 lenses, which work in consort to provide a rich visual image to the dragonfly. They are sight-based creatures who, with a quick turn of the head, are able to scan 360 degrees as well as above and below. Their vision probably allows them to discern individual wing beats, which to us would appear as a blur. They can see ultraviolet and polarized light. Many species also see well in dim light.
All of this information was found at http://www.mndragonfly.org/defined.html
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