i88i.] 
On Diptera as Spreaders of Disease. 
537 
far to explain obscure phenomena connected with the distri- 
bution of epidemics and their sudden outbreaks in unex- 
pected quarters. I have seen it stated that in former 
outbreaks of pestilence flies were remarkably numerous, and 
although mediaeval observations on Entomology are not to 
be taken without a grain of salt, the tradition is suggestive. 
Perhaps the Diptera have their seasons of unusual multi- 
plication and emigration. A wave of the common flea 
appears to have passed over Maidstone in August, 1880. 
We now see the way to some practical conclusions not 
without importance. Recognising a very considerable part 
of the order of Diptera, or two-winged flies, as agents in 
spreading disease, it surely follows that man should wage 
war against them in a much more systematic and consistent 
manner than at present. The destruction of the common 
house-fly by “papier Motive ,” by decoCtions of quassia, by 
various traps, and by the so-called “ Catch ’em alive,” is 
tried here and there, now and then, by some grocer, confec- 
tioner, or housewife angry at the spoliation and defilement 
caused by these little marauders. But there is no concerted 
continuous aCtion, — which after all would be neither difficult 
nor expensive, — and consequently no marked success. Ex- 
periments with a view of finding out new modes of fly-killing 
are few and far between. 
Everyone must occasionally have seen, in autumn, flies as 
if cemented to the window-pane, and surrounded with a 
whitish halo. That in some seasons numbers of flies thus 
perish, — that the phenomenon is due to a kind of fungus, the 
spores of which readily transfer the disease from one fly to 
another, — we know. But here our knowledge is at fault. 
We have not learnt why this fly-epidemic is more rife in 
some seasons than others. We are ignorant concerning the 
methods of multiplying this fungus at will, and of launching 
it against our enemies. We cannot tell whether it is capable 
of destroying Stomoxys calcitrans, the blowflies, gadflies, gnats, 
mosquitoes, &c. Experiment on these points is rendered 
difficult by the circumstance that the fungus is rarely pro- 
curable except in autumn, when some of the species we 
most need to destroy are not to be found. Another question 
is whether the fungus, if largely multiplied and widely spread, 
might not prove fatal to other than Dipterous inserts, espe- 
cially to the Hymenoptera, so many of which, in their cha- 
racter of plant-fertilisers, are highly useful, or rather 
essential to man. 
Another fungus, the so-called “ green muscardine ” (Isaria 
destructor), has been found so deadly to inserts that Prof. 
VOL. III. (THIRD SERIES). 2 N 
