HOUSEHOLD INSECTS 89 



beak, is frequently mistaken for it. The stable fly originated 

 in Africa from whence it has spread almost as extensively as 

 the housefly. It is a blood-sucking species, confining itself 

 mainly to the larger domestic animals which it torments dur- 

 ing the later months of the summer season. It does not enter 

 houses so commonly as the housefly, nor does it very fre- 

 quently bite human beings. It bites more commonly in damp 

 sticky weather and has thus given rise to the adage of the bit- 

 ing housefly. 



Several of the larger, noisy, metallic green or blue flies 

 that invade houses are species which live in the larval stages 

 upon decaying animal material. They can hardly be classed 

 as typical household insects. Our common species occur also 

 in Europe, but are probably native to both continents. 



Another very interesting fly which almost invariably ap- 

 pears on windows in the early spring of our temperate regions 

 is the cluster-fly (Pollenia rudis) . They are somewhat larger 

 than the housefly and of lazy, awkward flight. These flies 

 often occur in large clusters within window casings, entering 

 for hibernation and later seeking to escape through the glazed 

 windows, on the approach of spring. Although a very com- 

 mon insect, its larval habits remain unknown as there are no 

 authentic records of the flies having been reared. 



A very abundant and annoying, tiny fly makes its appear- 

 ance regularly in the latter part of the summer in most 

 households, and frequently persists far into the winter. 

 These little flies (Drosophila) live as larvae in decaying fruit, 

 with which they may easily be introduced. Our common 

 forms appear to have been brought hither in fruits from the 

 tropics, but their larvae will develop readily in the decaying 

 portions of most fruits or even the less strongly acid types of 

 pickles. The flies are very small and appear to come from 

 nowhere almost instantaneously when overripe fruit is ex- 

 posed. From a biological standpoint they are extremely in- 

 teresting as some of our most important recent discoveries 

 concerning the inheritance of color and other characters have 

 come from experimental studies of these tiny creatures. 



