176 THE DANGER OF FLIES 



rate of development. It is believed that many flies 

 pass the winter in the pupa state ; the adult fly also 

 survives the cold weather hidden away in cracks and 

 crevices, from which it may from time to time emerge 

 when the sun shines warmly. 



When the larvae are reared in too dry manure, they 

 attain only one -half their usual size. Too direct 

 warmth and the absence of moisture and available 

 semi-liquid food also tend to dwarf them. 



A word may be said about the distribution of the 

 insect. It is practically cosmopolitan. As Mr. Austen 

 records : 



' The British Museum collection, though very far from com- 

 plete, includes specimens from the following localities : Cyprus ; 

 North- West Provinces, India ; Wellesley Province, Straits 

 Settlements ; Hong Kong ; Japan ; Old Calabar ; Southern 

 Nigeria; Suez; Somaliland; British East Africa; Nyassaland; 

 Lake Tanganyika ; Transvaal ; Natal ; Sokotra ; Madagascar ; 

 St. Helena ; Madeira ; Nova Scotia ; Colorado ; Mexico ; 

 St. Lucia ; the West Indies ; Para, Brazil ; Monte Video, 

 Uruguay ; Argentine Republic ; Valparaiso, Chih ; Queens- 

 land ; New Zealand.' 



It is carried all over the world in ships and trains, 

 and seems to be equally at home in the high lati- 

 tudes of Finmark or in the humid heat of Equatorial 

 Brazil. 



The diseases which flies convey from man to man — 

 which rendered them by no means the least formidable 

 of the plagues of Egypt, and fully justified Beelzebub's 

 title of the ' Lord of Flies ' — are for the most part con- 

 veyed mechanically. The proboscis acts as an inocu- 

 latory needle. No part of the life -history of the 

 disease-causing organism must necessarily be carried 

 on in the body of the fly ; it is conveyed mechanically 

 and without change from an infected to a healthy 

 subject. The mouth parts can pick up the anthrax 

 bacillus, and if the fly then alight upon a wounded 



