I 



CHAPTER I I 



FLIES (DIPTERA) 



All of them are begotten of filth and nastiness, to which they 

 most willingly cleave, and resort especially to such places 

 which are so unclean and filthy ; unquiet are they, importunate, 

 hateful, troublesome, tumultuous, bold, saucy. 



Thomas Mouffet 



Louse-Flies, Mosquitoes, Midges, Black-Flies, 

 House-Flies, Blue-Bottles and Nest-Flies 



F WE could talk to birds as we talk to each other we would probably 

 find that flies loom very large in their lives and provide one of the 

 major topics of conversation. By day they form a favourite article of 

 diet for many birds, but during the night the tables are turned with a 

 vengeance. Incidentally it is an act of great cruelty to leave a canary 

 uncovered in a cage after dark, for it is then assailed by all the female 

 house-gnats, which, during the day, sit about silently on the walls and 

 ceiling of the room. 



Flies are carriers of many diseases of both man and birds, and from 

 this angle are certainly the most important group of insects. They are 

 distinguished by the possession of only one pair of membranous wings 

 (which are lost in some parasitic forms), the second pair being represent- 

 ed by an insignificant pair of knobbed appendages (halteres) which the 

 ancient writers mistook for "eyes hanging by their sides." These can be 

 clearly seen on Plate XXIX. A fly's head is joined to its thorax by a 

 slender flexible neck. The various component parts of the thorax are 

 fused, and this again is joined to the body by a distinct waist. The 

 mouth parts of the various types of flies are profoundly modified accord- 

 ing to the food they eat (Plate XII, a and c) but most of the parasitic 

 forms are blood-suckers. The metamorphosis of all flies is complete, 

 that is to say they pass through an egg, larval and pupal stage before 



FFC— P 2 1 1 



