ENTOMOLOGY

PHASES IN THE LIFE HISTORY OF NON-BITING FLIES 1~7HOUSE ~LY,l\IUSCA DOMESTICA LINNAEUS II(See Frontispiece)The commlni'house fly, Muaca domestica. is that insect charged withthe carriage of the greatest number of diseases, and probably justly, becauseof its frequentation of all types of excreta, garbage and waste,its common visitations to places where ·foods are handled, and also itsvisits to the human body. We have shown in the preceding lecture howit and its allies can carry disease and what diseases are charged againsteach. N ow we will take a brief review of its life history in order toarrive at important data for handling its control.The house fly adult is yellowish to dark gray in color, with four('quaUy broad longitudinal stripes on the thorax; first three abdominalsegments yellowish with a central black stripe and with two less distinctdiscal stripes. Thf' males measure 5.8 to 6.5 mm. in length, and thefemales 6.5 to 7.5 mm. The eyes in the male: are nearly contiguous andin the female are widely separated.This fly has been distributed by commerce to almost all parts of thecivilized 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 tipinto the haustellum bearing apically the oral lobes or labella. These lobf'sbfoar a large number of channels kept open by incomplete chitinous rings.( .llled pseudotracheae, which are fuUy described by Graham-Smith (1913).Tlu.' proboscis of the house fly is adapted to sucking and the absorptionof liquid or liquefied food. It cannot take up very large particles of solidfood. Nicoll (1911) found that the flies could not ingest particles larger~han .OM mm. This therefore determines the size of worm eggs which('an be ingested by the adult. We must assume therefore that whenlIies contain larger eggs, these were taken in by.the larva. Normally,• rt\ pver, the food must pass between the bifid extremities of the chitinousrlllgs of the pseudotracheal channels and pass along these to the mouth.These openings measure from .003 to .004 mm. in diameter. Solid particles,however, are heape!l up in a slight ridge in the channel between theoral. lobes and are prohably sucked into the oral pit and into themouth.When the fly feeds on dry substances such as sugar, dried specks ofmilk, or "putum, etc., it first liquefies the substance by a salivary secretionwhich flows into the oral pit and onto the substance, being distributedby the pseudotrll.cheal channels. The moistening is also aided• An appeal has been made to the International Commission for Zoological NomendJturefor the retention of Musca in .this sense with d()mesticQ; as type.