50 THE BOOK OF THE FLY 



unless it be with the object of leaving an unsatisfying 

 locality and discovering a better place. However, the 

 younger flies seem to feel no such restrictive influence, 

 for, as soon as they have become fit and the weather 

 suits, they show an inclination to fly high and thus may 

 travel to very remote places. It is just the same with 

 peacock, red admiral, and tortoise-shell butterflies, 

 which I have often reared and released for adding 

 to the interest and beauty of a flower garden. In 

 sunny weather many or most will soon wander never 

 to return ; those which have remained a few days 

 continue residence close round about, especially if 

 nettles, the food plant, grow in the neighbourhood. 



It would be of great interest if we could discover 

 how far a plague of flies arising from unsanatory 

 surroundings in one locality is liable to spread to the 

 injury of other localities. 



On this subject nothing useful can be said other 

 than can be safely surmised from the known habits of 

 the fly. The female has none of the attachment of the 

 honey-bee to its hive and community ; she is not 

 moved by an instinct like that of the wandering bumble- 

 bee in spring to found a colony ; she is indeed very 

 solicitous about the disposal of her eggs, but she is not 

 impelled by any desire to place successive deposits in 

 one locality. 



The lesser house-fly has proclivities similar to those 

 of the common house-fly, but probably she travels less 

 far afield although a little more inclined to outdoor 

 life. 



Very little is known about most of the common out- 

 door sweat- flies. Some breed in dung, and may be 



