ROACHES AND OTHER ANCIENT INSECTS
groups. Among the latter were dragonflies, and some of these must have been of gigantic size, for insects, because they attained a wing expanse of fully two feet, while the largest of modern dragonflies do not measure more than eight inches across the expanded wings. But the length of wing of the extinct giant dragonflies does not necessarily mean that the bulk of the body was much greater than that of the largest insects living today. In general, the insects of the past were of ordinary size, the majority of them probably matching with insects of the present time.
The modern dragonflies (Fig. 58) are noted for their rapid flight and for the ability to make instantaneous changes in the direction of their course while flying. These qualities enable them to catch other insects on the wing, which constitute their food. Their wings are provided with sets of special muscles, such as other insects do not possess, showing that the dragonflies are descended along a line of their own from their Carboniferous progenitors. They still retain a character of their ancestors in that they are unable to fold the wings flat over the back in the manner that most other insects fold their wings when they are not using them. The larger dragonflies hold the wings straight out from the sides of the body when at rest (Fig. 58); but a group of slender dragonflies, known as the damselflies (Plate 1, Fig. 2.), bring the wings together over the back in a vertical plane.
The dragonflies are usually found most abundantly in the neighborhood of open bodies of water. Over the unobstructed surface of the water the larger species find a convenient hunting ground; but a more important reason for their association with water is that they lay their eggs either in the water or in the stems of plants growing in or beside it. The young dragonflies (Fig. 59) are aquatic and must have an easy access to water. They are homely, often positively ugly, creatures, having none of the elegance of their parents. They feed on other living creatures which their swimming powers enable
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