366 
C. GORDON HEWITT. 
V. Natural Enemies and Occasional Parasites. 
The most important of all the natural enemies of M. 
domestica is the parasitic fungus Empusa muscae, which 
will be described here ; this is the most potent of the natural 
means of destruction. Of animals, apart from the higher 
animals such as birds, spiders probably account for the 
greatest number, though owing to the uormally clean con- 
dition of the modern house these enemies of the house-fly are 
refused admittance. I have been unable to rear any insect 
parasites, such as ichneumons, from M. domestica. Their 
life indoors and the cryptic habits of the larvm no doubt save 
them from the attacks of such insects; but Packard (1874) 
records the occurreuce of the pupa of what was probably a 
Dermestid beetle, which he figures; this was found in a pupa 
of M. domestica. Predatory beetles and their larvaB pro- 
bably destroy the larvm, and Berg (1898) states that a species 
of beetle, Trox suberosus F., known as “ Champi ” in 
S. America, is an indirect destructor of the common fly. I 
have frequently observed the common wasp, Vespa ger- 
man ic a, seize M. domestica and carry it away. In some 
places in India it is the custom, so I have been told by resi- 
dents, to employ a species of Mantis, one of the predatory 
“ praying insects,” to destroy the house-flies. 
In view of the fact that the Arachnids Chernes nodosus 
and the species of Gamasid are occasionally found actually 
attached in a firm manner to M. domestica, they will be 
described under this head, but it must be clearly understood 
that it is still an open question whether they are external 
parasites in the true sense of the word, or whether M. domes- 
tica, instead of being the host, is merely the transporting 
agent as it appears to be in the majority of cases. For the 
present they may be termed for convenience “ occasional 
parasites,” in view of the fact that they have been found 
occasionally feeding upon M. domestica. 
