Aug. 15. 1921 
Dispersion of Flies by Flight 
743 
we find that the percentage of marked flies recovered as compared with 
those liberated was 0.08 and 0.16, respectively (Tables II and IV). 
Another factor which should have reduced the proportion of the marked 
flies recovered in these two rings of traps in the first test was that many 
were captured in the two circles of traps nearer the point of release. This 
difference in the number of marked flies recovered in the two experiments 
seems to be chargeable logically to climatic conditions. On July 11 and 
the following days the temperature ran markedly higher than during the 
period immediately after the first liberation, and the humidity ran corre¬ 
spondingly lower. This would have the effect of reducing the longevity, 
and possibly causing flies to seek shelter and moisture rather than to 
disperse freely. 
The proportions of the several species among the marked flies released 
(estimated) and recovered, respectively, were as follows: Musca domestica , 
52 per cent and 32 per cent; Chrysomya macellaria , 36 per cent and 60 per 
cent; Phormia regina , 8 per cent and 6 per cent; other species 0.01 per cent 
and 1.53 per cent. The hot weather was probably a greater inhibiting 
factor in the case of the house fly and P. regina than in that of C. macel¬ 
laria. The optimum temperature is higher in the case of the last species. 
The make-up of the total catch in the recovery traps was not determined, 
but it was evident that there was a marked decrease in the total catch 
toward the end of the period and a marked reduction in the number of 
P. regina captured. 
distance; oe dispersion 
Numerous marked specimens of Musca domestica and Chrysomya 
macellaria reached the more distant ring of traps, several specimens of 
both species being recovered in trap No. 4 east, 5 miles from the point of 
liberation, and three specimens of C. macellaria in No. 4, 5 miles south. 
Not a single M . domestica was recovered in No. 4 south, however. 
Phormia regina also reached the outside ring of traps, one speci¬ 
men being taken in No. 4 south (5 miles), one in No. 4 west (3.75 
miles), and many in No. 3 west (3 miles). One specimen of Ophyra 
leucostoma Wied. was recovered in No. 4 west (3.75 miles) and one speci¬ 
men of O. aenescens Wied. in No. 3 north (3.4 miles). Only two 
specimens of Sarcophaga spp. were recovered, one in No. 3 west (3 miles) 
and one in No. 2 north (2.4 miles). The number of flies recovered at 
different distances is shown in detail in Table IV. 
DIRECTION OE SPREAD 
The individual species should be treated separately, but the several 
species recovered in the different directions seem to remain in about 
the same proportion with the exception of Phormia regina , which showed 
a marked tendency to go westward, 20 specimens (77 per cent) being 
taken in the west line of traps, while only two were taken in the traps in 
50937°—21-4 
