THE METAMORPHOSIS OF INSECTS 



169 



This is especially striking where the life of the young is entirely 

 different from that of the adult. The butterfly or moth may sip 

 nectar from any flower; but when the female lays her eggs, she selects 

 with unerring accuracy the particular kind of plant upon which her 

 larvae feed. The dragonfly which hunts its prey over the field, returns 

 to water and lays her eggs in such a position that the young when it 

 leaves the egg is either in or can readily find the element in which 

 alone it is fitted to live. 



The ichneumon-flies frequent flowers; but when the time comes 

 for a female to lay her eggs, she seeks the particular kind of larva 

 upon which the species is parasitic, and will lay her eggs in no other. 

 It' is a remarkable fact that no larva leads so secluded a life that it 

 cannot be found by its parasites. Thus the larvae of Tremex columba 

 bore in solid wood, where they are out of sight and protected by a 

 layer of wood and the bark of the tree in which they are boring; 



nevertheless the ichneumon-fly 

 Megarhyssa lunator, which is 

 parasitic upon it, places her eggs 

 in the burrows of the Tremex by 

 means of her long drill-like 

 ovipositor (Fig. i86). 



In contrast with the exam- 

 ples just cited, some insects 

 exhibit no remarkable instinct 

 in their egg-laying. Our com- 

 mon northern walking-stick, 

 Diapheromera, drops its eggs on 

 the ground under the shrubs 

 and trees upon which it feeds. 

 This, however, is sufficient pro- 

 vision, for the eggs are pro- 

 tected throughout the winter by 

 the fallen leaves, and the young when hatched, readily find their food. 

 Many species, the young of which feed upon foliage, lay their eggs 

 singly upon leaves; but many others, and this is especially tine of 

 those, the young of which are gregarious, lay their eggs in clusters. 

 In some cases, as in the squash bug, the mass of eggs is not protected 

 (Fig. 187) ; in others, where the duration of the egg-state is long, the 

 eggs are protected by some covering. The females of our tent- 

 caterpillars cover their eggs with a water-proof coating; and the 

 tussock moths of the genus Hemerocampa covertheir egg-clusters with 

 a frothy mass. 



Fig. 186. — Megarhyssa lunator. 



