78 



THE STUDY OF INSECTS 



ears, as northern children think; nor bring dead snakes to life, as colored 

 people in the South believe; but they are very fierce enemies to their 

 insect kindred. Their long, narrow, closely-netted wings are strong, carry- 

 ing them swiftly; and their jaws are powerful, and their appetites good; 

 so ii is an unfortunate insect that falls in their way. 



The nymphs of dragonflies are stout-bodied creatures usually resting 

 among the weeds in the water or in the silt at the bottom of a pond or 

 stream. The abdomen is wide and there are no external gills. They are 

 aquatic, for the female dragonflies lay their eggs either 

 in the stems of water-plants, in submerged logs, or in 

 wet mud or they simply fly down to the water and 

 wash off their eggs from the abdomen or, alighting on a 

 plant-stem, they push the long abdomen down into the 

 water and lay a mass of eggs on a submerged stem or 

 leaf. In any case when the eggs hatch the nymphs find 

 themselves in the water and at once swim off and hunt 

 for some smaller creatures to eat, for they are all 

 carnivorous and ferocious. 



They have strong legs and big jaws, and are real 

 insect ogres. The lower lip when extended reaches far 

 out, and is armed with powerful hooks with which to 

 grab their prey (Fig. 126) ; but when folded up it is so 

 large that it is called a mask and gives the insect's face 

 a comical resemblance to that of a bull-dog. These 

 nymphs have a peculiar method of breathing. The 

 caudal end of the alimentary canal is enlarged into a 

 chamber and lined with tracheae. The 

 nymph alternately draws water into 

 this cavity and expels it; and thus 

 the air in these tracheae is purified, 

 this part of the alimentary canal 

 acting as a tracheal gill. This process also helps the 

 insect in swimming, for the water may be expelled with 

 such force that the whole body is sent forward. 



When the nymph of a dragonfly is fully grown it 

 leaves the water to transform. The skin of the nymph 

 splits open on the back of the thorax and head, and 

 the adult emerges, leaving the empty skin of the nymph 

 clinging to the object upon which the transformation 

 took place (Fig. 127). 



There are two families of dragonflies, the Mschnidce, 

 and the Libclhdidce. 



Fig. 126. — Under 

 side of head of a 

 nymph of a damsel- 

 fly with labium un- 

 folded. (After Sharp.) 



Family ^schnid^ 



Fig. 127. — Exuviae of 

 nymph of dragonfly. 



The eeschnids are mostly large species; among them are the largest, 

 fleetest, and most voracious of our dragonflies. Some of them roam far 

 from water and are commonly seen coursing over lawns in the evening 

 twilight; but most of them fly over clear water. Some of the adults are 

 marked with bright blues and greens. The nymphs eat nearly any ani- 

 mal they can capture and hold. 



