350 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



The fact that the map shows the stations at which recaptures were 

 made to be mainly grouped in certain sections is due to the fact that 

 it was found necessary to cUscontinue the work somewhat eariier than 

 planned. Consequently the portion of the city remaining unworked 

 was covered very rapidly, but flies were captured at practicalh^ all 

 stations. A consideration of the areas covered by these last settings 

 gives further evidence of how generally the liberated flies were scat- 

 tered. For example, traps were placed at stations 31, 32, 33, 34, 35, 

 36, 37 and 38 from August 10 to 12 and flies were recovered from all 

 release points except the Laboratory. Placed again from August 12 

 to 14 flies were recovered from all points. Other areas show similar 

 results. 



It has previously been stated that the built-up portion of Miles City 

 was about two square miles in area. For the present purpose we may 

 consider that the Sales Yards was at one corner of a square containing 

 the city which is essentially correct. A breeding ground under usual 

 conditions is a center from which flies would normally spread equally 

 in all dii'ections given similar conditions. This would indicate that 

 flies from a breeding ground may spread over eight square miles of 

 territory, or by taking the longest radius encountered within city 

 limits (2,333 yards) we would get an area of nearl}^ five square miles, 

 and again by taking the longest radius actually encountered (3,500 

 yards) we get a territory of more than twelve square miles. 



These details are important as they indicate several facts of practical 

 significance — (1) that, given sufficient time, a given lot of flies from a 

 breeding ground will become quite evenly scattered over large areas, 

 (2) that even in a city of considerable size, every person allowing flies 

 to breed on his premises is maintaining a nuisance which directly con- 

 cerns every other individual residing in the city, (3) they emphasize 

 the importance of general cooperation in order to secure successful 

 results in control work (the cleaning up of a few places here and there 

 has little value), (4) they indicate the far-reaching effectiveness of 

 intensively applied control measures as a means of securing general 

 sanitary conditions. 



Concerning Time of Dispersion and Numbers of Flies. — Due 

 to the repeated lots of flies released and the several day intervals at 

 which traps were collected, the data concerning time required to 

 spread given distances has no great value. It does indicate some 

 facts, however. By reviewing the data for dispersion from the 

 Sales Yards, it is evident that flies from this release point spread over 

 the entire city, within a period of two to three weeks. From this 

 point 248,140 flies were released. The Laboratory release point, 

 on the other hand, represents only 35,270 house-flies and is comparable 



