FOREST ENTOMOLOGY. 



In the case of the Aphididse or greenfly, scale-insects, and plant-bugs, 

 the young in the first stage, whether hatched from eggs or produced 

 alive by the parent insect, resemble the perfect insect very much more 

 than those of beetles, moths, and flies. But whatever shape and form 

 they may take, the young insect in the first stage is always scientific- 

 ally known as a larva. We have in forest insects all forms and 

 classes of larvse, and this variety is of great interest as a biological 

 question. For instance, we find, as arboreal-feeding insects, active 

 six-legged larvae of a greenish colour, and harmonising with the foliage 

 or lichens on the bark ; while on the other hand we find the footless 

 whitish grub feeding within the wood. Thus we have two important 

 factors in the theory of evolution brought before us — viz., the absence 

 and apparent absence of legs through disuse, and the harmony of 

 colour to surroundings as a protection against natural enemies. 



In the larval stage the insect feeds voraciously, and as a rule grows 

 very fast. The skin of the creature, however, does not grow beyond 

 certain limits, and when this stage is arrived at, the creature halts, as 

 it were, throws ofli" its skin, assumes a fresh coat, often of a different 

 colour, and again commences feeding. This 

 process is known as moulting, and occurs 

 several times during the larval stage until full 

 growth is reached. The duration of larval 

 life in arboreal insects is very varied indeed. 

 In some cases the period occupies only a few 

 days, in others several years. 



The pupa, or third stage of the life of an 

 insect, is a period of rest or quiescence, when 

 the insect takes no food. It is the period of 

 quiet transformation, when the ugly crawling 

 caterpillar is being transformed into the beauti- 

 ful moth, or the carrion maggot into the swift 

 airy fly. The pupal forms and habits of forest 

 insects are very varied. Thus in beetles all the 

 parts of the future insect are visible, saw-flies 

 and moths form cocoons, and the two-winged 

 flies form cases. Some descend into the ground 

 to pupate, while others form hard cases on the food-plant. Fig. 4 may 

 be considered, for general purposes, as a typical pupa. 



The stages thus referred to — viz., egg, larva, and pupa — are the 



Fig. i.— Typical pupal form 

 of a II insect. (From draw- 

 ing by Mr G. A. Dunlop.) 



