J. E. M. Mellor 55 



with the fly pest by method 1 — destruction of the adult. Howard's 

 figures (1912) give an unnecessarily alarming idea of the number of 

 descendants from a single pair of flies. Graham-Smith (1916) showed 

 that the descendants of each female blowfly during the season numbered 

 130 individuals instead of 1012 millions. 



In Howard's calculations no account was taken of natural dangers, 

 such as lack of food, the ravages of carnivorous larvae, hymenopterous 

 parasites and inclement weather. 



On the other hand, the escape of but a few females may be sufficient 

 to ensure the continuance of the multitudes of flies. Moreover, owing 

 to the extremely short preoviposition^ period, the chance of killing the 

 majority of females before they oviposit seems to be very meagre. 



Griffiths (1908), working in England, found this period to be 10 days 

 in the case of M. domestical; Hewitt (1910), also working in England, 

 found it to be 14 days. Bishop, Dove and Parman (1915), working in 

 Dallas, Texas, found the period to be only 4 days in summer and not 

 less than 10 days in spring and autumn. 



At present all that can be expected of this method is temporary local 

 relief, such as the clearance of hospital wards, of individual rooms, etc. — ■ 

 and this only when fresh invaders are prevented from entering by placing 

 muslin or wire screens over windows and doors. Such screens tend to 

 diminish the freshness of any breeze entering, and so cause some dis- 

 comfort in hot climates. Whilst trying to reduce the swarms of flies at 

 a military hospital in Serbia, in 1915, I had to resort to method 1, owing 

 to the lack of sufficient means to attack the breeding places successfully. 

 I found it difficult to get some men to refrain from tearing the muslin 

 placed over the ward windows, and impossible to get muslin-covered 

 swing-doors, especially made for the kitchen, kept closed. The cooks, 

 who were peasants, complained that the muslin kept out the breeze, and, 

 not realising the danger to which they were exposing the hospital, pre- 

 ferred flies and breeze to no flies and less air; and the Commandant was 

 not sufficiently alive to such matters to be aware of the advisabiUty 

 of enforcing the necessary regulations. Those wards, in which the 

 necessary precautions were observed daily, were kept almost free from 

 flies to the great relief of the patients. 



^ The period between escape from the puparium and oviposition, during which the fly 

 becomes sexually mature and copulation takes place. 



- Musca domestica forms at least 90 per cent, of the flies frequenting houses and is, 

 therefore, the most dangerous. (Hermes, 1911, p. 521, quoted by Graham-Smith, 1914, 

 p. 79.) 



