Au?. 15, 1921 
Dispersion of Flies by Flight 
739 
DIRECTION OR DISPERSION 
The data obtained in regard to the direction of flight were interesting. 
The total number of marked flies recovered in the different directions from 
the point of liberation was as follows: West, 1,289; north, 1,745; cast, 
1,184; south, 434. Of course the different species should really be dis¬ 
cussed separately in treating of the direction or distance of dispersion; 
the figures show, however, that for some reason the liberated flies of all 
species failed to be recovered in the traps south of the point of liberation 
in numbers in proportion to those recovered in the other directions. 
Considering the house fly and screw-worm fly in regard to the numbers 
traveling in different directions, it will be seen in the case of the house 
fly that 889 (24.66 per cent) were recovered in the west traps, 1,325 
(36.76 per cent) in the north, 1,067 (29.38 per cent) in the east, and 331 
(9.18 per cent) in the south. In the case of the screw-worm fly 364 
(38.11 per cent) were recovered in the west, 388 (40.62 per cent) in the 
north, hi (11.62 per cent) in the east, and 92 (9.63 per cent) in the south 
traps. In an attempt to correlate these figures with the direction of the 
wind it appears that there is a tendency exhibited in this test for both of 
these species to go with the wind rather than against it, as will be seen 
by referring to climatological data in Table III. The prevailing wind 
during the first five days was from the south and east. 
The fact that more house flies were recovered in the east traps than in 
tlie west is not quite in accord with the idea that they may have traveled 
largely with the wind, since there was no west wind but a considerable 
amount of east wind. With Chrysomya macellaria , however, there were 
less than a third as many in the east traps as in the west, the north traps 
caught the greatest number, and the south traps less than one-fourth 
as many as were caught in the north. The fact that the wind was more 
or less choppy throughout the period makes it very difficult to draw any 
conclusions on its exact influence on dispersion. Numerous other factors 
which must be considered also tend to make the drawing of conclusions 
on this point hazardous. 
If we attempted to account for the greater catch of flies in certain lines 
of traps over others by the traffic along the highways we would expect to 
find the greatest dispersion east and west, probably greater to the west, 
and about equal to the north and south, but such was not the case. 
Considering the possibility of the attraction of feeding and breeding 
places or volume of odors, we would expect, at least for Musca domestica , 
the greatest movement westward toward the city of Dallas, but the 
figures do not accord with this idea. It is probable that the proximity 
of smaller centers of attraction, such as farmhouses, barns, etc., are more 
effective in influencing the spread than more distant but larger attrac¬ 
tive areas. These conditions, however, were apparently quite similar 
in each direction. As Chrysomya macellaria and Phormia regina are 
