FLIGHT OF anopheij:s 213 



breeding-places they have traveled passively. They may be carried by a light 

 wind but in that case the limit is two kilometers. Dr. J. M. Young, of the 

 British Army, after extensive observations in China, came to the conclusion that 

 as a rule malarial mosquitoes will not fly over two hundred yards. 



Stephens and Christophers, however, in their reports on the malaria expedi- 

 tion to Sierra Leone, state that under some conditions Anopheles may fly much 

 greater distances than has been supposed. In one small inland house which had 

 been occupied by one old man, five and six Anopheles were to be caught each 

 morning. These were fresh from pupae and could only be derived from the 

 breeding-place three to four hundred yards away. The same writers have also 

 demonstrated a flight of six hundred yards. The Eoyal Society's malarial com- 

 mission in India found that, in certain villages in the central provinces, Anoph- 

 eles cuUcifacies, A. stephensi, and A. fuliginosus were always present if there 

 were extensive breeding-places within a quarter of a mile, but that villages which 

 were distant half a mile from these breeding-places contained few or no malarial 

 mosquitoes. The obvious conclusion is that half a mile was beyond the normal 

 flight. James and Liston point out that in Mian Mir three groups of rain-pools 

 gave an opportunity to make fresh observations upon this question of flight. The 

 first group was four hundred and fifty yards distant from any house ; the second 

 seven hundred and fifty yards distant ; and the third upwards of three-quarters 

 of a mile. " On repeated occasions the pools of the first group were found to 

 contain larva? within a week of a shower of rain, on three out of four occasions 

 the pools of the second group contained larvae, but on no occasion were larvae 

 found in the pools of the third group. These experiments appeared to show that 

 A. ross-i, which was the species concerned, would readily fly to a breeding place a 

 quarter of a mile away, that it would less readily fly to a breeding-place 750 yards 

 away, and that it would never fly to breeding places three-quarters of a mile away. 

 It is obvious, however, that from none of these experiments can any knowl- 

 edge of the maximum flight of ' anopheles ' be obtained ; they prove only that 

 when these insects are once established in a village they naturally select the 

 nearer breeding places in preference to those which are further away. But in 

 their search for food adult ' anopheles ' often become attracted to villages which 

 have no breeding places near at hand, and recent observations have shown that 

 they may be abundant in a place even when there are no breeding grounds within 

 a very long distance. Captain James, I. M. S., in the operations at Mian Mir 

 already referred to, found on one occasion that numerous adult A. fuliginosus 

 were present in the bazaars and houses when no larvae of this species were to be 

 found nearer than two and a quarter miles, and Dr. Christophers, during the 

 same operations, found that the limit of flight of A. rossi had not been reached at 

 three-quarters of a mile, and that although all breeding places of this species 

 had been obliterated up to this distance, it still appeared in increasing numbers 

 in the houses. The latter observer draws the following conclusions from his 

 experiments : — 



" (1) In every case where an abundant food supply existed, anopheles 

 travelled long distances (half a mile or more) to reach it, and traversed an equal 



