Aug. 15, 1921 
Dispersion of Flies by Flight 763 
12 days, Chrysomya macellaria 7 to 8 days, Phormia regina 5 to 6 days, 
Lucilia sericata 5 to 6 days, Sarcophaga spp. 11 to 12 days, Ophyra 
leucostoma 3 to 4 days. Second test at Dallas (radius of dispersion 
5 miles), M . domestica 9 to 11 days, C. macellaria 9 to 11 days, P. regina 
8 to 10 days, Sarcophaga spp. 2 to 4 days, O. aenescens 6 to 8 days. 
Third test at Dallas (radius of dispersion 8 miles), M. domestica 15 days, 
C. macellaria 17 days, O. aenescens 4 days. Fourth test at Dallas (radius 
of dispersion 17 miles), M. domestica 8 to 9 days, C. macellaria 10 to 11 
days, P. regina 10 to 11 days, O. leucostoma 1 to 5 days. 
In considering the radius of dispersion it should be borne in mind 
that the marked flies may not necessarily have remained constantly 
within the circle with the radius given but may have returned into it 
after more extended travel. 
STIMULI AFFECTING DISPERSION 
The evidence gained points toward the operation of several stimuli in 
initiating and governing dispersion. Under the conditions obtaining 
in nature these stimuli seem to be so blended or mixed as to make it 
impossible to weigh their relative importance or, in fact, to determine 
the nature of some of them. It seems probable that the strength of 
these stimuli and even their character vary with different species. 
The importance of food and favorable breeding places as stimuli is 
clearly shown by the recovery of the greater numbers of specimens of a 
species in traps located near favorable feeding and breeding grounds. 
Behind this immediate desire of the individual to obtain food and find 
a suitable breeding place there appears to be an inherent tendency to 
disperse. There seems to be some evidence that the house fly was in¬ 
fluenced in regard to direction of dispersion by the proximity of farm 
buildings and towns, indicating spread from one attractive point to 
another, rather than long sustained flight. 
The recovery of males as well as females far from the point of libera¬ 
tion indicates strong dispersion tendencies in that sex as well as in the 
females. Since mating does not usually take place immediately after 
emergence, it is no doubt important for the males to seek breeding places 
where the females are to be found, and they are also attracted to food 
though not so strongly as are the females. 
The question has often been asked, do the flies when liberated tend 
to return to their original habitat; in other words, is the homing instinct 
developed? These tests were not planned to determine this point, 
though they happen to give data on it. The figures presented under 
the discussion of direction of flight clearly show that there is no marked 
tendency for any of the species to travel back toward their original 
place of capture. In this connection it should be remembered that in 
the first and second tests at Dallas the west traps were nearly in line 
