262 SUMMARY AND CONCLUSIONS 



intestinal canal. Though they are very greatly attracted to such 

 ova in faecal deposits, the part they play in their dissemination 

 under natural conditions has not been ascertained (Chapter XX). 

 The larvae of some species of non-biting flies cause myiasis 

 of various kinds in man. Some live in the tissues lining 

 natural cavities or in wounds, causing serious loss of tissue, 

 extensive wounds and even death. Others live under the skin, 

 and are the cause of much irritation, and the larva of one species 

 sucks blood from wounds which it produces. The larvfe of 

 several species have been found in the intestinal tract, occa- 

 sionally giving rise to uncomfortable sensations, or even serious 

 inconvenience and ill-health, but often producing no symptoms 

 (Chapter xxi). 



In temperate climates adult flies appear to be subject only to 

 one serious disease, that caused by the fungus, Ejupusa vu/sccb, 

 which destroys large numbers in the late summer and early 

 autumn. If some means could be devised of artificially infecting 

 flies with this fungus, a ready means of controlling their numbers 

 would be obtained (Chapter xxiii). 



Externally various parasites, such as mites and false-scorpions, 

 are often found on flies. These creatures, some of which live on 

 various articles of human food, such as cheese, are undoubtedly 

 transported to fresh feeding grounds by flies, but it is at present 

 doubtful whether the majority of them feed on the flies. 

 Internally various species of flies, especially in the tropics, are 

 infested with flagellate protozoon parasites, and nematode 

 worms. 



Larvae and pupa^ are frequently destroyed by parasitic 

 hymenoptera (Chapter XXiv). 



The natural enemies of flies and their larva, such as spiders, 

 wasps, ants, predaceous flies, lizards, toads and birds, probably 

 destroy large numbers, but are incapable of effectually checking 

 their multiplication (Chapter XXV). 



Many species of flies breed in or visit human excrement. 

 Of these the most important house-frequenting species are 

 M. dojiiestica, F. canicularis and F. scalaris, though several others 

 are occasionally found in houses. In camps on the other hand 

 many excrement frequenting species visit food, and under 



