ORDER DIPTERA: SCHIZOPHORA: THE MUSCOIDEA 153 



Thus, in the tropics the whole term of development from 

 egg to adult may be fulfilled in about ten days, and in a hot 

 summer in England in about a fortnight ; but under unfavour- 

 able conditions of temperature it may continue for nearly 

 three months. 



In dealing with the house-fly as a pest, gauze and fliy- 

 papers are merely palliatives. The way to suppress flies is, 

 as with mosquitoes, to make a clean sweep of breeding- 

 places. House refuse, street sweepings, and rubbish of all 

 sorts should be incinerated, or, if this be impossible, should 

 be carted several miles from centres of population and dumped 

 to leeward of prevalent winds. Latrine-stuff should be 

 buried deep enough to prevent any emergence of flies from 

 maggots that may have got into it at the source. Horse- 

 dung required for use should be shot far from the house and 

 treated with quick-lime, and the heap should be forked and 

 spread frequently so that fowls and wild birds may get at 

 any maggots and pupae that it may contain. Colonel 

 Thornhill emphasises the necessity of using infinite care in 

 carting away filth to trenching-grounds ; if it be allowed to 

 drip from the carts the whole route becomes a breeding- 

 ground for flies. 



Genus Calliphora : Blue-bottles, or Blow-flies. The species 

 of this cosmopolitan genus are larger than those of Musca, 



Fig. 52 —y^iz of Ulow-fly. Fia. 53.— Larva of Blow-fly. 



and are of a blue-black or black colour. The cheeks are 

 broad and hairy ; there is a vertical row of bristles on each 

 hypopleuron ; and there are bristles on the inner edge of the 

 tibiae of the middle legs. Blow-flies are particularly attracted 

 to meat and offal, on which they lay their eggs (Fig. 52) in 

 sticky clusters. It is possible that they may sometimes 

 deposit their eggs in foul wounds, or in the nostrils of the 

 living subject ; or that their eggs or maggots may be 

 swallowed in food and may thus get into the bowel. Fig. 53 

 represents the maggot, and Fig. 54 the pupa, enlarged. The 



