HOUSEHOLD INSECTS 237 



stripe and a dark tip. The venation of the wing (fig. 61) 

 should be carefully noted, because the course of the fourth 

 longitudinal vein serves to distinguish this insect from 

 other flies. In many towns of Great Britain, and even of 

 other countries, the house-fly population has from time to 

 time been subjected to a census. Taking an average of 

 these investigations in this country, it is found that ninety- 

 five per cent, are true house flies, Musca domestica, and 

 the balance is composed of the lesser house fly, Fannia 

 canicularis, the blow fly or blue-bottle, Calliphora ery- 

 throcephala, the stable fly, Stomoxys calcitrans, the fly 

 which the Americans call the stable fly, Muscina stabulans, 

 and others. 



The lesser house fly, Fannia canicularis, so closely 

 resembles the house fly in general appearance, except for 

 its smaller size, that it is popularly considered to be a 

 young house fly ; as a matter of fact, the adult fly does not 

 grow ; when it emerges from the pupa it has attained its 

 full growth and no further increase in size takes place. 

 Apart from its size, the fact that the fourth longitudinal 

 vein of the wing runs straight to the margin, instead of 

 bending at an angle (fig. 61), serves to distinguish the house 

 fly from the lesser house fly. The thorax, too, is striped 

 with three, instead of four, dark lines, and the abdomen is 

 more pointed than in the house fly. The characteristic, 

 jerky flight of these flies, usually near the ceiling or round a 

 gas bracket, is quite unlike the heavier more laboured flight 

 of Musca domestica. In habits the two flies are somewhat 

 similar. The lesser house fly appears earlier in the year 

 than the true house fly and also disappears earlier. Ovi- 

 position takes place either in decaying animal or vegetable 

 matter. The eggs resemble those of Musca domestica, but 

 the larvae (fig. 62) are quite unlike those of the house fly. 

 About a quarter of an inch in length, considerably flattened, 

 and armed with a double row of spines down the back and 

 a double row down each side of the body, they are quite 



