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 Acarns 

 miiscarum. Berlese has reared from stable flies what 

 he considers as this Acarus miiscaruni 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 



