FLIES AND OTHER HOUSEHOLD INSECTS 39 



Control measures. Badly infested houses can be cleared of 

 these pests most easily by thorough and perhaps repeated fumiga- 

 tions with hydrocyanic acid gas as described on page 48. Carbon 

 bisulfid, has also been advised as a fumigant. On account of the 

 inflammability of the latter, we would prefer to use in houses the 

 somewhat more poisonous hydrocyanic acid gas. Carbon bisulfid 

 with its heavy fumes is particularly adapted to the destruction 

 of these pests in the holds of vessels. 



A still safer method of fumigation consists in burning pyrethrum 

 in infested compartments. It is stated that the vapors of this 

 insecticide are frequently more effective in destroying roaches 

 than the use of the powder itself. The room should be kept closed 

 from six to ten hours. The smoke of burning gunpowder is also 

 very obnoxious and deadly to roaches, particularly the black Eng- 



Fig. 21 Croton bug: a, h, c, d, successive stages in the development of the young; 

 e, adult; f, female, with egg case; g, egg case enlarged; h, adult, with wings spread; all 

 natural size except g. (After Riley) 



lish roach. The moistened powder should be molded into cones, 

 placed in an empty fireplace and ignited. It is especially valuable 

 in the case of old houses. 



There are a number of roach poisons placed upon the market and 

 some of these are undoubtedly very efficacious, particularly if 

 assisted by persistent cleanliness and the eradication of inaccessible 

 haunts, so far as possible. We would further suggest the testing of 

 naphthalene in the flake form, as described on page 27, as a means 

 of at least partially suppressing this pest. The liberal use of Per- 

 sian insect powder or pyrethrum is also of service in destroying these 

 insects. The paralyzed cockroaches should be swept up and burned. 



A relatively simple method, described by Mr Tepper of Aus- 

 tralia, is to mix plaster of paris one part, and flour three or four 



