TMAOTNAL LIFE. 



29 



The life of the imago. 



The life of the imago varies much in length in the different groups. 

 Reproduction being the principal business of this period, the imago com- 

 monly dies as soon as mating and egg-laying are completed. In the moths 

 and butterflies, courtship, mating and egg-laying may occupy a few days 

 or more rarely a faw weeks. The imago has no necessity to provide 

 for her young further than by laying her eggs in a suitable place. 



In the Hymenoptera, on the other hand, the parent has to provide for 

 her young or actually feed them, as the larval period is one of helplessness 

 during which the grub feeds on the stored up food or is fed by the 

 parent ; so also the life of the imago is prolonged until she has fully 

 provided for the new generation or done her share of the work of the 

 nest. Between these two extremes are many shorter or longer imaginal 

 lives. Climatic conditions may determine the length of the life as in the 

 grasshoppers and locusts, the Bombay locust living as imago for nine 

 months until it can lay eggs, whilst allied grasshoppers live as imago for 

 some six weeks only. The May-flies live for very short periods, the long 

 nymphal life being the active period. The 

 dragon-flies, on the other hand, have a long 

 life both as nymphs and imagines. Coleop- 

 tera live long and can survive long periods 

 when food is scarce and they are waiting 

 until conditions are again favourable for 

 egg-laying. Hemiptera and Dipt era have 

 long lives as imagines, the preliminary 

 stages being proportionately shortened. 

 There is no general rule and it varies from 

 species to species. The activities of an 

 insect are not to be measured by its life in 

 the winged state when it is most apparent 

 to us, but by its whole free life as larva or 



Fm. 40. 



Wingless female Wasp. 

 (The male is ivinged.) 



nymph and as imago. In some the first predominates, in others the latter. 

 In exceptional cases, both sexes are not equally developed, and in 

 general it is the females which are the least developed. In the " Bag- 

 worms ", the female remains as an imperfect pupa and does not become 

 winged or leave the shelter of the larval case, whilst the male becomes 

 winged and seeks the female (fig. 41). In other moths the female may 

 be active but unwinged. In the Aphides , the females are frequently 

 unwinged, the males winged. This is the invariable rule in the Scale 

 Insects and IVfealy Bugs, in which the females only moult twice ancj 



