78 INSECT PESTS 



Why are the females of some moths wingless ? Here 

 is a little story in evolution which we may as well look 

 at in passing. 



These moths are usually in their adult stage during the 

 cold season, when most insects are dormant and most 

 birds have to go hungry. The obvious connexion between 

 these two facts will at once be seen. Clearly the compara- 

 tively heavy-bodied female would want considerable wing- 

 expanse to carry her about, and would therefore be a most 

 conspicuous object for the famished robins, thrushes and 

 sparrows. As a result those females who were wily 

 enough to hide up had the privilege of continuing the 

 race, whilst the giddier girls were picked off, and so selec- 

 tion has brought about in the course of ages these apterous 

 females whose disused wing-stumps are all that remain 

 to remind them of their former soaring capabilities. 



Why have we been " blessed " with the Winter Moths in 

 our orchards ? It is not because we have robbed these 

 creatures of their natural food, for their larvse eat white- 

 thorn, blackthorn, birch, hornbeam, oak, hazel and other 

 forest trees, as well as apple, pear, plum and cherry. 

 It is another case where we have departed from the 

 ordered path of Nature. We have substituted a superior 

 for the wild food, and as a consequence these Uttle moths 

 come gaily to the feast, exactly as the Cabbage butter- 

 flies do in the kitchen garden. There, however, the 

 ichneumon parasite has a good deal to say in the matter 

 that is to our advantage. 



The Winter Moths, although preyed upon to some 

 extent by muscid and ichneumon flies, and subjects for 

 the cannibaUsm of such caterpillars as that of the Dunbar 

 Moth, are not yet so well under control. Here, I fancy, 

 we are witnessing the intermediate stage. Presently 

 Nature will say " Stop ! " to the Winter Moths and then 

 an ichneumon or other fly will be found increasing by 

 hundreds and thousands until the plague of green cater- 

 pillars is a thing of the past. 



