PHASES IN THE LIFE HISTORY OF NON-BITING FLIES 135 



Riley (plate III, fig. 1) and S. robust a Aldrich are also among the most, 

 common flesh flies. 



Froggatt (1915) has given a very fine treatment of the most impor- 

 tant sheep maggot flies and has presented colored illustrations of some 

 of them. 



All of these flies are likely to be found in houses and markets and 

 when given the opportunity will lay eggs on meat offered for sale or 

 exposed in kitchens or mess halls. If this meat is already cooked there is 

 a good chance of the eggs being ingested and giving rise to gastrointestinal 

 myiasis. But the danger from flesh flies is greater than the mere 

 causation of external or internal myiasis. The flies which lay the eggs 

 may have bred in diseased carcasses, and if so, proba,bly will deposit with 

 the eggs a glutinous film containing bacteria from these carcasses, for it 

 will be remembered that the fly larva takes up these bacteria and they 

 may remain in its body until it as a mature fly lays its eggs, and even 

 longer. It must be borne in mind that because conditions in the imme- 

 diate vicinity are sanitary, does not mean that the flies which come 

 are sanitary, because Bishopp and Laake (1919) record the flight of 

 marked Chrysomya macellaria flies for 15 miles, and of Phormia regina 

 for 11 miles. 



OTHER EXCREMENT BREEDERS 



Others of our house flies, as the non-biting stable fly, Mti^cina 

 stdbvlcms Macquart (plate III, fig. 2), the lesser house fly Fcmrna canv- 

 cularis Linnaeus (plate III, fig. 3), and the latrine fly F. scalaris 

 Fabricius breed in decaying vegetables and animal matter. 



Muscina stabidans looks very much like the house fly, but it is a 

 little more robust. It is gray and the thorax is marked with four 

 longitudinal black lines. Parts of the legs and scutellum are reddish. 

 The principal differential character is in the wing venation. The larva, 

 however, is easily distinguished from Musca domestica, by the six-lobed 

 anterior spiracles and the anal stigmal plates scarcely elevated, less 

 than their diameter apart, each with three very short slits pointing 

 towards those of the opposite plate. It breeds in decaying and live vege- 

 table matter, human and animal excreta, and has even been reared from 

 insect puparia. It breeds likewise in raw and cooked meats and on car- 

 casses. It is therefore a very potential disease carrier, possessing all 

 the opportunities of the house fly, with which it may already be mixed 

 in medical literature. 



Farmia canicidaris and F. scalaris are two flies commonly found in 

 houses, which greatly resemble the house fly, but the former may be dis- 

 tinguished by the presence of only three dark stripes on the thorax 

 instead of the four found in the house fly. The larvae of these flies are very 



