TRAPPING AND POISONING 327 



a stable where a few horses are kept, STOO flies were caught in 

 two days, 12,000 ni one da}^ and 18,000 in one and a half days. 

 The trap is illustrated in fig. 101, and the following is a descrip- 

 tion of its construction : It measures twenty-four inches long, 

 twelve inches high and eight inches wide. The screen used for 

 the large receptacle A and the roof-shaped entrances C is ordinary 

 Avire fly or mosquito screen. The upper portion A serves as a 

 receptacle for the captured flies; it rests on a board B which 

 carries two roof-shaped entrances C open at the top to permit the 

 entry of the flies into A. The middle board B rests on a base 

 board D from which it is separated by means of small pieces of 

 wood E about half an inch in thickness fastened at the corners as 

 shown. Upon the base board D rest two tin bait-pans P, separated 

 by about one-quarter of an inch from the middle board B. The 

 trap may be baited with any attractive substance such as meat 

 scraps, raw fish scraps, bread and milk, etc. The captured flies 

 may be killed by immersing the trap in hot water or by pouring 

 boiling water over it. 



Hodge (1911) has taken advantage of the attractive power 

 which the garbage or refuse can has for flies and has devised a 

 trap which can be attached to the lid of the garbage can ; the lid 

 is so arranged that it does not fit tightly on to the can but a 

 quarter of an inch space permits the flies to enter and on leaving 

 they naturally fly upwards and enter the trap which consists of 

 an ordinary balloon wire fly-trap. In such a trap baited with 

 attractive food such as fish heads, etc., he has caught as many as 

 2.500 flies in fifty minutes. He has also made another device 

 consisting of overlapping screens of wire-gauze (see Hodge, 1913) 

 which can be fitted to the window of the stable or cowshed and 

 catches the flies as they leave the same. 



Poisoning. 



The arsenical fly-papers or pads were among the earliest fly 

 poisons. 



Formalin or formaldehyde has been employed in recent years 

 with marked success in most cases. Sometimes complete failure 

 has been reported, but in such cases I have often found that it 



