Dragonflies undergo a type of development known as incomplete metamorphosis in which the aquatic larvae (sometime called nymphs) undergo a series of moults; the stages between moults are known as instars or 'stadia' (4). After hatching from eggs, the larvae develop quickly through the summer; they enter their final instar during the autumn of the following year, and then enter 'diapause', a form of hibernation, before emerging as adults early the next summer (2). In the first few instars, the larvae swim by undulating the body from side-to-side; later on they develop a system of jet-propulsion which enables them to easily escape from predators such as water bugs, fish, other dragonfly larvae and beetles. The larvae of the emperor dragonfly are themselves voracious predators, armed with fearsome mouthparts known as a 'mask'; the mask is normally tucked under the head, but is rapidly extended in under 25 milliseconds (4), piercing prey as large as small fish (2).
After diapause, final instar larvae leave the water and crawl up vegetation. The adult emerges, leaving the discarded skin of the nymph attached to the plant (5). The new adults undergo a period of feeding and maturation before starting to reproduce (4). Males set up territories, which they defend fiercely against other males; they fly rapidly at two to six metres over the water, and very rarely come to a rest. During mating, males and females form a typical 'wheel' mating posture, in which the male grabs the female behind her head using the claspers at the tip of his abdomen. After mating the female lays her eggs in floating vegetation, keeping low to avoid encounters with territorial males (2).