No. 430.] THE DIFFUSION OF INSECTS. 799 
at all, — the direction depending on that of the wind ; anda wind 
prevailing from the same direction during the breeding season 
one year would affect a certain territory, while the following 
year the prevailing winds might be from another quarter, and 
so cause these insects to terrorize an entirely different section 
of country. Formerly, and before the advent of the electric 
motor as a means of propelling street cars, when these gnats 
developed, during some seasons, in the St. Francis bottoms, 
across the Mississippi River west of Memphis, Tenn., these 
insects might occur in their breeding grounds in immense 
swarms, but so long as the prevailing winds were from an 
easterly direction few of them would be observed in Memphis ; 
but let a strong gale set in suddenly from the west and these 
. bloodthirsty insects would suddenly appear in such numbers as 
to prevent the running of the street cars, which were then 
drawn by mules; these last would be killed in their harnesses, 
and the cars were necessarily abandoned until these gnats 
disappeared. Of course the introduction of electricity, and the 
disappearance of the mules as a means of motive power has, 
in this case, overcome the difficulty, but former conditions 
offered a good illustration of the far-reaching influences of the 
wind on some insects. It may be mentioned that the gnats 
that were so driven about by the wind were all sterile females 
and the species was not, in this particular case, permanently 
diffused by this means. Somewhat similar effects of winds 
are to be observed as affecting the various species of migra- 
tory locusts, the exact territory devastated by them often being 
dependent on the direction of the prevailing winds during the 
migrating season. 
Relative to the concluding point in this paper, viz., the influ- 
ence of wind and thunderstorms combined on insect diffusion, 
I beg to call attention to a most interesting series of papers 
contributed to Prometheus, a German scientific journal much 
like our Scientific American, by Prof. Karl Sajo, of Budapest, 
Hungary. Professor Sajó says that it is known that “ before 
thunderstorms the crayfish come out of the water into the 
grass on the banks of the river or lake; many fishes act as if 
they were insane, and many birds and mammalia become 
