PHASES IN THE LIFE HISTORY OF NON-BITING FLIES 127 



HOUSE FLY, MUSCA DOMESTICA LINNAEUS " 



(See Frontispiece) 



The common house fly, Musca domestica, is that insect charged with 

 the carriage of the greatest number of diseases, and probably justly, be- 

 cause of its frequentation of all types of excreta, garbage and waste, 

 its common visitations to places where foods are handled, and also its 

 visits to the human body. We have shown in the preceding lecture how 

 it and its allies can carr}' disease and what diseases are charged against 

 each. Now we will take a brief review of its life history in order to 

 arrive at important data for handling its control. 



The house fly adult is jellowish to dark gray in color, with four 

 equally broad longitudinal stripes on the thorax ; first three abdominal 

 segments yellowish with a central black stripe and with two less distinct 

 discal stripes. The males measure 5.8 to 6.5 mm. in length, and the 

 females 6.5 to 7.5 mm. The eyes in the male are nearly contiguous and 

 in the female are widely separated. 



This fly has been distributed by commerce to almost all parts of the 

 civilized world. 



Certain features of its anatomy are of interest in the present study. 



The head is prolonged to form a proboscis which is enlarged at tip 

 into the haustellum bearing apically the oral lobes or labella. These lobes 

 bear a large number of channels kept open by incomplete chitinous rings 

 called pseudotracheae, which are fully described by Graham-Smith (1913). 

 The proboscis of the house fly is adapted to sucking and the absorption 

 of liquid or liquefied food. It cannot take up very large particles of solid 

 food. Nicoll (1911) found that the flies could not ingest particles larger 

 than .045 mm. This therefore determines the size of worm eggs which 

 can be ingested by the adult. We must assume therefore that when 

 flies contain larger eggs, these were taken in by the larva. Normally, 

 however, the food must pass between the bifid extremities of the chitinous 

 rings of the pseudotracheal channels and pass along these to the mouth. 

 These openings measure from .003 to .004 mm. in diameter. Solid par- 

 ticles, however, are heaped up in a slight ridge in the channel between the 

 oral lobes and are probably sucked into ' the oral pit and into the 

 mouth. 



When the fly feeds on dry substances such as sugar, dried specks of 

 milk, or sputum, etc., it first liquefies the substance b^^ a salivary secre- 

 tion M^hich flows into the oral pit and onto the substance, being dis- 

 tributed by the pseudotracheal channels. The moistening is also aided 



° An appeal has been made to the International Commission for Zoological Nomen- 

 clature for the retention of Musca in this sense with domestica as type. 



