Odonata (dragonflies and damselflies) are insects with an incomplete metamorphosis (hemimetabolous). The aquatic larva or nymph hatches from an egg, and develops through eight to seventeen instars before leaving the water and emerging as the winged adult or imago. Imago The imago (adult stage) has a large head, well-developed, compound eyes, legs that facilitate catching prey (largely other insects) in flight, two pairs of long, transparent wings that move independently, and an elongated abdomen. Many Odonata are relatively large insects, but wingspans range from 17 mm (some Agriocnemis damselflies) to 191 mm (helicopter damselfly Megaloprepus coerulatus. The largest dragonflies have a wingspan of up to 160 mm, but they are much more massive than any damselfly. Head The globular compound eyes each have up to 28000 ommatidia and provide sharp color vision; On the forehead there are three ocelli, which can distinguish light from dark, and help with orientation in flight. The two short antennae are tactile receptors. The mouthparts are on the underside of the head and include simple chewing mandibles. Thorax The front segment of the thorax (prothorax) carries a pair of legs, and the synthorax carries the middle and rear legs and both pairs of wings. A dark stripe (humeral stripe) often follows the humeral suture, which runs from the base of the front wing towards the base of the middle leg. A paler antehumeral stripe is often found above the humeral stripe. Wings The wings have a network of veins; between the veins the wings are generally transparent, but may be partly colored. In most Odonata there is a structure on the leading edge near the tip of the wing called the pterostigma. This is a thickened, hemolymph–filled and often colorful area bounded by veins. The functions of the pterostigma are not fully known, but it most probably has an aerodynamic effect and may also have a visual function. More mass at the end of the wing may also reduce the energy needed to move the wings up and down. The right combination of wing stiffness and wing mass could reduce the energy consumption of flying. There are five main vein stems on dragonfly and damselfly wings, and wing veins are fused at their bases. The main veins are: Costa (C) – at the leading edge of the wing, strong and marginal, extends to the apex of the wing. Subcosta (Sc) – second longitudinal vein, it