Aug. 15, 1921 
Dispersion of Flies by Flight 
755 
cited. The first of these was in a village and most decidedly a house-fly 
environment, as indicated by a catch of 361 gm., of which 92 per cent 
were house flies. No. 4 was in a field removed from human habitations 
and hence more favorable for screw-worm flies. Here 78 per cent of the 
548 gm. taken were screw-worm flies. Now note the number of marked 
flies recovered: Trap No. 3, 5 house flies and no screw-worm flies; trap 
No. 4, 28 screw-worm flies and no house flies. 
It seems evident that those positions favorable for the capture of large 
numbers of one or more species of flies must be in the favorite haunts of 
/^E/FCETA/T 
O /O RO 30 <50 OO 
eercemtage ofm. domest/ca/// 7vtal cr7ch 
PERCENTAGE OE MARKED M.DOMESTfCA AMONG MARRED PL/EG RECODEREO 
-■■■Hi PERCENTAGE OF C.MAC ELLAR/A /N TOTAL CATCH 
(llllllUUlUlllllliy PERCENTAGE OP MARKED CJfACELLARfA AMONG MARKED fl/ES RECOVERED 
Fig. 3 *—Diagram showing percentage of each species taken in each direction from point of liberation in 
the third dispersion test at Dallas, Tex. First, percentage of house flies in each direction as compared 
with total house flies caught; second, percentage of marked house flies as compared with the total marked 
house flies recovered; third, percentage of screw-worm flies in each direction as compared with total 
catch of this species; fourth, percentage of marked screw-worm flies as compared with the total marked 
screw-worm flies recovered. 
the species so taken and that marked specimens in their movements 
would, like others, tend to congregate in such positions. Furthermore, 
it would appear that those traps so located as to catch the largest number 
of flies of a given species would have a better chance of capturing marked 
specimens. It is true that the occurrence of favorable breeding and 
feeding places in the immediate environs of a trap would favor large 
catches, but these very conditions would tend to assemble migrating 
marked individuals near the trap. 
It was at first thought that by weighing the relative advantages of the 
positions of the traps in the capture of house flies and screw-worm flies 
