How Insects Cause or Carry Disease 49 



Not infrequently the larvae of certain flies are 

 to be found in the alimentary canal where as a rule 

 they do no particular damage. Altogether the 

 larvae of over twenty different species of flies have 

 been found in or expelled from the human in- 

 testinal canal. In Europe, the majority of these 

 larvae belong to a fly which looks very much like 

 the house-fly except that it is somewhat smaller 

 and so is often known as "the little house-fly" 

 (Fig. 29) (Homalomyia canicularis). The same 

 species is very common in the United States, fre- 

 quently occurring in houses. Under certain con- 

 ditions it may even be more abundant than the 

 house-fly. It is believed that the larvae in the in- 

 testinal canal come from eggs that have been de- 

 posited on the victim while using an outdoor privy 

 where the flies are often very abundant. Instances 

 are also on record where these larvae have been 

 discharged from the urethra. 



Another fly (Ochromyia anthropophaga) occur- 

 ring in the Congo region has a blood-sucking larvae 

 which is known as the Congo floor-maggot. The 

 fly which is itself not troublesome deposits its eggs 

 in the cracks and crevices of the mud floors of the 

 huts. The larvae which hatch from these crawl out 

 at night and suck the blood of the victim that may 

 be sleeping on the floor or on a low bed. 



