80 THE FLY. 



highly developed species are found, and where, too, they exist 

 in still greater abundance. 



One author observes : — " To a geographical distribution of the 

 widest extent, the flies add a range of habits of the most diversi- 

 fied nature ; they are both animal and vegetable feeders, an 

 enormous number of their species acting as scavengers in consum- 

 ing putrescent and decomposing matter of both kinds. Many are 

 parasitic." 



The same author observes : — " Considered in relation to man, 

 there would seem to be sufficient reason for placing this apparently 

 feeble order at the head of our insect enemies. Allowing for the 

 good effected by the clearing away of animal and vegetable impu- 

 rities by many species, and for the indirect advantage caused by the 

 known instances of a few others assisting in the fecundation of 

 plants, there remains a long list of direct injuries effected by Dipiera. 

 Without laying undue stress upon the formation of galls and other 

 vegetable deteriorations caused by many species, there can be no 

 doubt that the destruction of grass-lands by the larva of the Crane- 

 fly, or Daddy Long-legs, Tipiila oleracea, of olive-crops by Dacus, 

 of oranges by Ceratitis^ of various culinary plants by others, and 

 of wheat and other crops by the Hessian-fly, are of very serious 

 consequence. Our domestic animals, moreover, suffer from the 

 Bot-fly, the Tick, and the Gad-fly. Still more dreaded is 

 the Tsetse-fly, Glossina inorsitans^ which is of sufficient power 

 to prevent the exploration of a region in which it occurs. 

 Nor is man himself spared. The petty inconveniences of wasted 

 food, broken rest, and slight personal pain, experienced in tempe- 

 rate regions from fly-larvae, gnats, midges, etc., are aggravated in 

 both warmer and more boreal countries to a dangerous extent, and 

 have been even found prejudicial to life. One of the flies, 

 Lucilia hoininovorax^ is known to have caused considerable 

 destruction to human life among French convicts in Cayenne, by 

 laying its eggs in the mouth or nostrils during sleep." 



As to annoyance, most of us have had our own experience. 

 We have felt the venom of the Gnat, and perhaps of the Gad-fly. 

 In the warm summer, swarms of flies settle on the heads of 

 horses and cows. They creep into the eyes and ears of these 

 animals, in order to feast upon the humours there secreted. This 



