68 THE HABITS AND BIONOMICS OF THE HOUSE-FLY 



found in large numbers out-of-doors but when it becomes cloudy, 

 or should it rain, they retire indoors. 



In August 1906, Dr M. B. Arnold (see Niven, 1907) carried out 

 some exact experiments at the Monsall Fevei' Hospital, Manchester, 

 on the distance travelled by flies. Three hundred flies were captured 

 alive and marked with a spot of white enamel on the back of the 

 thorax. These marked flies were then liberated in fine weather. 

 Out of the 300 five were recovered in fly traps at distances varying 

 from 30 to 190 yards from the place of liberation and all the 

 recoveries were within five days. The maximum distance of 190 

 yards was determined by the limitations of the hospital grounds 

 and did not indicate the possible limit of flight. 



In the summer of 1907 when visiting the Channel Islands 

 I found M. domestica from 1^ to 2 miles from any house or any 

 likely breeding place so far as I was able to discover. The fact 

 that the house-fly is able to fly at a considerable height above 

 gi-ound is indicated by the fact that I have frequently found them 

 flying at an altitude of 80 feet above the ground. Flight at so 

 great a height conjoined with a steady wind would enable them to 

 cover a considerable distance. 



Howard (1911) records an experiment of J. S. Hine who caught 

 350 flies and marked them with gold enamel before liberation. 

 Flies so marked were observed about dwellings from 20 to 40 rods 

 (600 to 1200 yards) from the point of liberation up to the third 

 day. Hine states : " It appears most likely that the distance flies 

 may travel to reach dwellings is controlled by circumstances. 

 Almost any reasonable distance may be covered by a fly under 

 compulsion to reach food or shelter. When these are close at hand 

 the insect is not compelled to go far and, consequently, does not do 

 S(x" The experiments which I am about to mention, however, 

 show that flies will travel a considerable distance even where 

 houses occur. The same author also states that Prof S. A. Forbes 

 had experiments carried out in which it was sho^^^l that marked 

 flies spread naturally for at least a quarter of a mile. 



An interesting and valuable series of experiments on the i-ange 

 of flight of flies under rural conditions was carried out by Copeman, 

 Howlett and Merriman (1911), an opportunity being afforded by 

 an unusual plague of house-flies in the neighbourhood of a small 



