36 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 12 



Fig. 1. — Diagram of the sewage purification plant where work against sprinkling 

 sewage Filter Fly was carried out. Raw sewage enters at A, passes through B, C, 

 D, E and H, and the purified effluent escapes through I. The flies are produced in E. 



A — Stream of raw sewage; B — Screen for removing coarse matter; C — Preliminary settling tanks; D — Siphon 

 dosing tanks; E — Sprinkling filters; F and G — Galleries leading the sewage into and out of the sprinkling filters; 

 H — Final settling tanks; I — Stream of effluent. 



Chsetopoda, Crustacea, Arachidna, and Insecta. The exact part 

 which each group of organisms plays in the process of sewage purifica- 

 tion is still an unsolved problem. The Psychoda are, however, con- 

 cerned in the reducing of the gel- 

 atinous and amorphous film, living 

 in it and consuming it. The prin- 

 cipal species of Psychoda found do- 

 ing this work at the Plainfield 

 sprinkling sewage filter is Psychoda 

 alternata. 



Nature and Extent of Injury 



So far as the present studies have 

 gone there is nothing whatever to 

 show that the Sprinkling Sewage 

 Filter Fly in any way damages or 

 interferes with the efficiency of the 

 society to which it belongs. The 

 adult flies, however, emerging in 

 enormous numbers throughout the 



Fig. 2. — Diagram showing relation of 

 film to stone. A, Stone; B, Film. 



fore-part and throughout the latter part of the warm season, fly or are 

 wind-carried for a distance of at least three-fourths of a mile, penetrate 

 the finest screens and fall into the food which is presently to be con- 

 sumed by people. Knowing the source of these flies and seeing them 

 in the food, is sufficient to convince the people concerned that almost 

 any infection from which they may subsequently sufl"er has been 

 brought to them by this agencj' and to cause them to file suits for dam- 

 age against the concern or the municipality maintaining the sewage 



Plate 1. General view of the preliminary settling tanks (A), the sprinkling filter 

 (B) and the final settling tanks (C). Sewage passes through in the order named. 

 The flies breed in the sprinkling filter. 



