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 pro- 

 vided 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 pro- 

 genitors. 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 



[95] 



