14 RODENTS OF IOWA 



animal is worthy of consideration from an economic stand|)oint 

 if it is sufficiently abundant and is in some wa>' or other detrimental 

 to man 's best interests. Nature seeks to maintain a proper ' ' bal- 

 ance" among all the forms of life on the globe, but when .man 

 steps in and interferes with this great plan some penalty must often 

 be paid. When the numbers of any species of animal are main- 

 tained at about the normal, the damage done is so slight as to be 

 almost negligible. If, however, the numbers of any species, through 

 some cause or other, reach a point far above normal, their habits 

 and even their presence make them worthy of consideration. The 

 kind and quality of the food destroyed are matters rather of sec- 

 ondary importance. Since many of the rodents are prolific breed- 

 ers and most of them are also hearty eaters, methods of control 

 and remedial measures of various kinds are often of considerable 

 value. 



In the main, the system of classification and arrangement of 

 species here adopted is that employed by Cory in "The Mammals 

 of Illinois and Wisconsin."^ In some cases, however, a later sys- 

 tem has been followed. Attempt has not been made to include all 

 the forms which "possibly" or "probably" occur within the 

 state, but for the most part, only those appear of which certain 

 and authentic records are available. For this reason and because 

 of the fact that many of the species have been split up into a 

 greater or lesser number of subspecies and geographic races, it is 

 possible that some forms not mentioned in these pages should be 

 added, but the main object of the paper will not have been de- 

 feated on this account. In the preparation of this bulletin data 

 have been drawn freely from Cory's work and from the various 

 papers published by the United States Biological Survey. Other 

 articles which have proved of value are included in the list of 

 references. Tender every species and subspecies reference is given 

 to the first publication of the specific or subspeeific name. 



During the preparation of the present work various parts of the 

 state have been visited for the purpose of observation and the se- 

 curing of material. In addition, the assistance of others has been 

 invited, so that the list of those who have contributed in some way 

 or other is rather a long one. The following persons have thus 

 aided materially in the securing of specimens from which many 

 locality records were obtained: 



*Cory, Charles B., The Mammals of Illinois and Wisconsin : Field Mus. Nat. 

 Hist., Pub. 153, Zool. Ser. XI, 1912. 



