(110) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 351 



are representative of the average occurrence, as I have 

 observed, of the different species. 



For the proportional occurrence in similar localities we have 

 interesting figures given by Howard (1900) for the United 

 States. Of 23,087 flies caught in rooms where food supplies 

 are exposed he found that 22,808, or 98'8 per cent, of the 

 whole number, were M. domestica, and of the remaining 

 1'2 per cent. H. canicularis was the commonest species. 

 Hairier (1908) found that more than nine tenths of the flies 

 caught in the kitchens and " living-rooms " of houses in the 

 neighbourhood of depots for horse-refuse, manure, etc., were 

 M. domestica. In a further report Hamer gives more 

 details as to the different species that were found. In one 

 lot of 35,000 flies caught on four fly-papers exposed in similar 

 positions, 17 percent, were Homalomyia canicularis, less 

 than 1 per cent. wereC. erythrocephala, and considerably 

 less than 1 per cent, were Muscina stabulans, whereas of 

 nearly 6000 flies caught in another situation in four fly- 

 balloons 24 per cent, were H. canicularis, 15 per cent, were 

 C. erythrocephala, and nearly 2 percent, were M. stabu- 

 lans. He gives an interesting diagram showing from counts 

 of flies the seasonal prevalence which I have previously 

 recorded from observation. The report shows how the pro- 

 portions of the different species vary in different situations 

 according to the substances and refuse that are present in 

 the locality. We may therefore say with certainty that 

 M. domestica is the commonest species of house-fly, and 

 next to this H. canicularis, and that in country houses 

 S. calci trans often occurs in large numbers, although 

 it is not a house-fly in the strict sense of the word. 



III. FLIES OCCURRING AS CO-INHABITANTS OF HOUSES WITH 



M. DOMESTICA OR AS VlSITANTS. 



We have seen from the preceding section that M. domes- 

 tica is by far the commonest species which occurs in houses, 

 and is, in fact, " domesticated" in the true sense of the word 



