CONTROL OF INJURIOUS MAMMALS 163 



dens. In the eastern states fumigation has been found more effective, 

 carbon disulphide being the cheapest and best, three teaspoonfuls 

 being placed on cotton or other absorbent material and dropped into 

 the burrow, then the burrow closed to retain the fumes. It is inflam- 

 mable and explosive, hence smoking should not be indulged in when 

 handling it. Calcium cyanide is also used. It is a dangerous poison and 

 should be handled with great care. The exhaust fumes from an au- 

 tomobile engine are sometimes used effectively. 16 



In the war against the destructive rodents of the fields and pas- 

 tures, the U. S. Biological Survey is cooperating with farmers and 

 stockmen as it does in the eradication of coyotes and other predaceous 

 animals. In one year its agents directed campaigns against prairie-dogs 

 and ground squirrels over 18,000,000 acres of farm and range lands, 

 with the help of 132,000 farmers, thus saving in one season $i 1,000,000 

 worth of crops. 17 The smaller rodents that live in burrows may be de- 

 stroyed as woodchucks are, by the fumes of carbon disulphide, cotton 

 containing a teaspoonful of the fluid being dropped into the hole, 

 which should then be covered to confine the fumes for several hours, 

 but the cheapest and most effective method is to drop poisoned grain 

 into the burrows. There are formulae for preparing poisons, directions 

 for trapping and other pertinent information in most of the publica- 

 tions on economic mammalogy. 18 Pellett says that the best repellant 



16 Silver, Woodchuck control in the eastern states, U. S. Dept. Agric. Leaflet No. 

 21, 1928. 



17 Bell, Death to rodents, Yearbook U. S. Dept. Agric. for 1920, pp. 421-438. 



18 Lantz, Use of poisons for destroying noxious animals, Yearbook U. S. Dept. 

 Agric. for 1908, pp. 421-432; Destroying rodent pests on the farm, ibid., for 1916, 

 PP- 381-398; Pocket gophers as enemies of trees, ibid., for 1909, pp. 209-218; Meadow 

 mice in relation to agriculture and horticulture, ibid., for 1905, pp. 363-3735 An 

 economic study of field mice, U. S. Biol. Surv. Bull. No. 31, 1907; Directions for 

 destroying pocket gophers, ibid., Circular No. 52, 1908; Rodent pests of the farm, 

 Farmers' Bull., No. 932, 1918. Bailey, N. Amer. Fauna, No. 49, pp. 51-52, 1926. 

 Piper, The Nevada mouse plague of 1907-8, Farmers' Bull, No. 352, 1909; Mouse 

 plagues: Their control and prevention, Yearbook U. S. Dept. Agric. for 1908, pp. 

 301-310. Dearborn, Trapping on the farm, ibid., for 1919, pp. 451-484. Burnett, The 

 Wyoming spermophile or ground squirrel, Office Colorado State Entom. Circular 

 No. 9, 1913 ; Meadow mice, ibid., No. 18, 1916 ; The Wyoming ground squirrel in 

 Colorado, with suggestions for control, ibid., No. 20, 1917; Suggestions for com- 

 bating prairie-dogs and ground squirrels, ibid., No. 24, 1917. Dixon, Rodents and 

 reclamation in the Imperial Valley, Journ. Mammalogy, in, 136-146, 1922; Control 

 of the California ground squirrel, California Agric. Exper. Sta. Circular No. 181, 

 1917. Dixon apd deOng, Control of the pocket gopher in California, California Agric. 

 Exper. Sta. Bull. No. 281, 1917. Merriam, The California ground squirrels, U. S. Biol. 

 Surv. Circular No. 76, 1910. Birdseye, Some common mammals of western Mon- 

 tana in relation to agriculture and spotted fever, Farmers' Bull. No. 481, 1912. 

 Scheffer, American moles as agricultural pests and fur producers, Farmers' Bull., 

 No. 1247, 1922 (superceding Nos. 583 and 833). Bruner, Pocket gophers, Univ. Ne- 

 braska Agric. Exper. Sta. Press Bull., No. 29, 1908. Silver, Mouse control in field 

 and orchard, Farmers' Bull, No. 1397, 1924. 



