56 AN ECONOMIC STUDY OF FIELD MICE. 



OTHER MECHANICAL DEVICES. 



Mechanical methods of destroying voles have long been in use, and 

 sometimes are effective. In some countries where the animals are 

 abundant, considerable reliance is placed upon the efforts of laborers 

 armed with spades and other digging tools and assisted by dogs. In 

 this manner thousands are sometimes killed. 



Trenching also is a favorite method of catching both mice and 

 moles. Trenches a foot and a half deep are dug at intervals about the 

 infested lands. They £ re wider at the bottom than at the top, or have 

 perpendicular sides. The animals fall into these pits and are unable 

 to climb out. Men and dogs regularly make the rounds and despatch 

 the animals thus caught. This method was used effectively in Dean 

 and New Forests in 1813 and 1814 and in the later vole plagues of 

 Great Britain and central Europe. 



Inundation with water and fumigation with sulphur have been em- 

 ployed to some extent in killing field mice. All these mechanical 

 methods involve much labor and are slow and often expensive. 



POISONING. 



As the laying out of poison for wild animals is attended by danger 

 to other animals and to human beings, it should never be intrusted to 

 the ignorant or careless. In some countries the laying of poison is 

 forbidden by law, and several of our own States have enactments 

 regulating the practice or forbidding it. The majority of States have 

 no legislation prohibiting the use of poison, and the matter is usually 

 left to the judgment of the individual farmer, to whom attaches re- 

 sponsibility for any damage that may result through his carelessness. 



Strychnine. 



All things considered, strychnine is the most satisfactory poison for 

 field mice. Although a very deadly substance, it is less dangerous to 

 handle than either phosphorus Or potassium cyanide. Its extreme 

 bitterness renders it less liable to be mistaken for a harmless drug. 

 Nevertheless, every precaution should be taken in handling it. The 

 strychnine salt most used commercially is strychnia sulphate. This is 

 the best for poisoning purposes, since it is soluble in boiling water, 

 while the alkaloid requires the presence of an acid for its solution. 

 To disguise the bitterness of the poison when employed for rodents, 

 sugar is used, or the strychnine may be mixed with its own bulk of 

 commercial saccharine. 



For poisoning field mice various baits may be recommended, such 

 as wheat, oatmeal, and corn, among the grains, and seeds of various 

 plants, as the tomato, dandelion, sunflower, and others. The bait 

 should be soaked over night in a poisoned sirup, which may be pre- 

 pared as follows; 



