1881.] The Destruction of Noisome Insects. 605 
covered with a well-charaCterised growth of Empusa. The 
Stomoxys calcitrans died about the same time, but with less 
distinctly marked symptoms. It did not become cemented 
to the glass, but was found on its back at the bottom of the 
compartment. Over its body there was a white fungoid 
growth, agreeing with that on the common flies, though 
much slighter. The blowflies, which had taken much more 
frequent liberties with the infectious specimens than any of 
their fellow-prisoners, showed not the slightest trace of the 
disease ; they buzzed about vigorously whenever the sun 
shone, and died finally without any traces of Empusa upon 
their bodies. 
I resolved upon a more decisive experiment. I found two 
more common flies which had just died of the disease, and 
catching two lively blowflies I applied the spores of the 
fungus to their bodies by means of a camePs-hair pencil, 
going over both the thorax and abdomen, and in particular 
the region about the spiracles. I then turned the blow- 
flies into the same vivarium, and watched what might 
happen. To my surprise they manifested no symptom of 
the disease, and died after about a fortnight an apparently 
natural death. 
Hence it appears that, at least under the circumstances 
of the above experiments, this disease is not communicable 
to the blowfly. 
It may further be added that the infeCtiousness of Empusa 
muscce, even among the common house-fly, is not very great. 
The specimens which we find dead of this affeCtion never 
form any at all high percentage of the flies infesting our 
houses. If we consider how these inserts are given to touch 
each other, as if in a sort of game, and how they crawl over 
those of their fellows who have fallen victims to the Empusa, 
we are led to wonder that the disease is not more widely 
spread. Whether it may be possible by any artificial culti- 
vation to render this fungus more abundant and more easily 
transferred from one individual to another, it would be pre- 
mature to decide. 
I may here briefly notice some interesting results on the 
use of the Pyrethrum as an insecticide, an account of which 
in full is to be found in the “American Naturalist ” for last 
month. The powder of this plant is not, as popularly ima- 
gined, a universal insecticide. It is indeed very doubtful if 
such a specific exists. But the Pyrethrum most unfortu- 
nately aCts most intensely and certainly where its efficacy 
is least to be desired. All the Hymenoptera are said to 
succumb most readily. Now this order includes so very few 
