FLIES AND TYPHOID FEVER. 



253 



In all 23,087 flies were examined.* They were caught in rooms 

 in which food supplies are ordinarily exposed, and may safely he said 

 to have been attracted by the presence of these food supplies. Of 

 these 23,087 flies, 22,808 were Musca domestica; that is to say, 98.8 per 

 cent, of the whole number captured belonged to the species known as 

 the common house-fly. The remainder, consisting of 1.2 per cent, of 

 the whole, comprised various species, the most significant ones being 

 Homaloymia canicularis (the species ordinarily known as the 'little 

 house-fly'), of which 81 specimens were captured; the stable-fly 

 (Muscina stabulans), 37 specimens; Plwra femorata, 33; Lucilia ccesar 

 (screw-worm fly), 8; Drosophila amelophila, 15; Sarcophagatrivialis, 10; 

 and Calliphora erythrocephala (the common blow-fly), 7. 



Musca domestica is, therefore, the species of greatest importance from 



Fig. 5. Sph.erocera subsultans- 

 enlarged. 



Fig. 6. Phormia terr;enov.e- 

 enlarged. 



the food-infesting standpoint; Homaloymia canicularis is important 

 and Muscina stabulans is of somewhat lesser importance. Drosophila 

 amelophila, although not occurring in the former list of abundant 

 species, does rarely breed in excreta and is an important form; it would 

 have been much more abundant in the records of house captures had 

 more of these been made in the autumn, after fruit makes its appear- 

 ance upon the dining tables and sideboards, since this species is the 

 commonest of the little fruit-flies which are seen flying about ripe 

 fruit in the fall of the year. The Calliphora and the Lucilia are of 

 slight importance, not only on account of their rarity in houses, but 

 because they are not, strictly speaking, true excrement insects. They 



* The determination work in the Diptera was all done by the writer's assistant, Mr. D. W. 

 Coquillett, who is an authority on this group of insects. 



