Aug. 15,1921 
Dispersion of Flies by Flight 
753 
It is peculiar that all four of the specimens of Ophyra aenescens were 
taken in a single trap, No. 1 north. Little is known of the habits and 
responses to various stimuli of this species, but we usually think of it as 
being most abundant under rural conditions and in no sense a domestic 
species. These flies appear to be attracted to a considerable extent 
by carcasses in their last stages of decay and to some extent by hog 
manure. 
RAPIDITY OF FLIGHT 
Probably the best method of indicating the rapidity of dispersion 
from the point of release is by tabulating the number of marked speci¬ 
mens recovered in the various traps on succeeding days. These data 
are given in Table VIII. While it might appear that the house fly 
traveled very slowly to the west, none being recovered during the first 
5 days, the fact that some marked specimens were taken in the most 
remote recovery trap in that direction on that date would indicate that 
this must be explained on some other basis than the time required to 
reach the traps. It will be noted that one marked specimen was taken 
in trap No. 3 north, 7.1 miles from the point of liberation, on the day 
following release, and two specimens were taken in trap No. 2 south, 6.1 
miles, on the same day. The first specimen reaching No. 4 east, 7.9 
miles, was on the fourth day after release. As no marked specimens were 
captured in traps No. 4 north and No. 3 and 4 south, any further state¬ 
ment as to the rapidity of dispersion to the outside of the 8-mile circle 
is hazardous. The fact that more marked flies were taken in the re¬ 
covery traps on the first day than on any subsequent date after release 
indicates that spread of this species is rapid. 
The large number of screw-worm flies recovered in all the traps on the 
first day after release indicates a very rapid and thorough dispersion 
of this species promptly after release. It is notable that more marked 
specimens were taken in the outside circle of traps, approximately 8 
miles, on the first day following release than on any subsequent day. 
Of course the recoveries were affected markedly by temperatures as 
indicated by the comparatively few specimens taken on September 21 
and 22 and the larger number taken September 24, which was a mild 
day. No doubt low temperatures would retard dissemination, but 
they would also have the effect of rendering the baits in the recovery 
traps less attractive and hence, even though the marked flies were in 
the vicinity, they might not be captured. 
It would appear that in the case of neither the house fly nor the screw- 
worm fly were the recoveries any more gradual in the outer rings of 
traps than in the closer ones. In other words, there did not seem to be 
any percolation of the flies outward from the point of release. This, of 
course, would be influenced by the choppy wind condition already men¬ 
tioned, provided the wind is a dominant factor in dispersion. 
