NATURAL ENEMIES 
77 
on the fly, but when the fly reaches a place similar to 
that inhabited by the mites the latter drop off, cast 
their skins, and start new colonies. DeGeer observed 
large numbers of these tiny mites on the back and neck 
of the house fly. Linnaeus named one of them Acariis 
muscarnm. Berlese has reared from stable flies what 
he considers as this Acariis mtiscarum of Linnaeus, and 
finds that the adult belongs to the genus Histiostoma. 
The hypopi most commonly found on the house fly are 
those of the common household cheese- ham- and flour- 
mites. All through the summer months, and in warm 
houses during the winter months, these creatures breed 
with astonishing rapidity and fecundity. The females 
bring forth their young alive, and these in turn reach 
full growth and reproduce until a cheese, once infested 
by a few, swarms with the crawling multitude which 
causes its solid mass to crumble and become mixed with 
excremental pellets and cast-off skins. 
During the summer months the mites are soft-bodied 
and have comparatively feeble powers of locomotion, 
and, as they become numerous enough to devour 
the whole of a cheese with no other food at hand, it 
was for a long time a puzzle to know what became of 
them and to understand how a cheese could become in¬ 
fested without coming in contact with another infested 
cheese or without being placed in an infested room. It 
has been learned, however, that when necessity requires 
it and when the insects happen to be in the proper stage 
of growth, they have the power not only of almost in¬ 
definitely prolonging existence but of undergoing a 
