BUREAU OF BIOLOGICAL SURVEY. 539 



the assistants of the survey with the view to discover effective methods 

 of ridding large tracts of the above and other tick-carrying animals. 

 A prime requisite of such methods is cheapness, since, while in its 

 most virulent form the spotted fever is confined to a comparatively 

 small area on one side of the Bitterroot Valley, the disease in milder 

 form is distributed over thousands of square miles in the Rocky 

 JVloiiutain region, including parts of several States. 



To disseminate the information thus far obtained and to aid in the 

 study of the disease, a circular has been published and distributed 

 giving a list of the wild manmials living in and around the valley and 

 indicating the species which are known to act as hosts of the tick. 



CRAWFISH IN RELATION TO AGRICULTURE. 



In certain sections of the South crawfish exist in very great num- 

 bers, especially in Mississippi and Alabama, where there is a single 

 tract of more than 1,000 square miles where the raising of cotton and 

 corn is rendered difficult and in places unprofitable by these crus- 

 taceans, which devour the young and tender plants. Some idea of 

 the numbers of crawfish may be gained from the statement that in 

 badly infested areas there are frorn 10,000 to 12,000 holes to the acre, 

 each hole being made by a single crustacean. Investigations and 

 experiments made on the ground show that at a comparatively small 

 expense it is possible to practically free a given tract from the pests 

 by the use of carbon bisulphid, two or three drops to a hole, and by 

 employing men to kill the craw^fish when they emerge on rainy morn- 

 ings or evenings to feed. A circular on the subject describing the 

 habits of the animals, so far as they concern the planter, and sug- 

 cesting methods of killing them by means of chemicals is in course of 

 preparation, and when published will be freely distributed in the 

 sections where crawfish are troublesome. 



BIOLOGICAL INVESTIGATIONS. 



Field work during the year was carried on in Alabama, Arkansas, 

 Idaho, Kentuclrv, Montana, Tennessee, Wyoming, and Virginia. 



The final report on the biological survey of Colorado has been 

 published. It includes description of the life and crop zones of the 

 State, with a zone map; also a full list of the mammals, with im- 

 portant contributions to our loiowledge of their abundance, distri- 

 bution, and relations to agriculture. 



The biological survey of New Mexico also has been finished, and 

 final reports on the life and crop zones, with a zone map, and full 

 reports on the mammals and birds, are nearly complete. 



The biological surveys of previously unworked parts of both Idaho 

 and Montana have been made as part of the general survey of these 

 rapidly developing States. A previously unknown species of ground 

 squirrel was found to be abundant in Idaho. The animal is of con- 

 siderable economic importance, owing to the damage it does to crops 

 throughout some of the best farming country. 



The biological survey of the lower iMississippi Valley region has 

 been continued, and a report on the birds of Arkansas, including 

 notes on distribution areas and a map of the life and crop zones, ha.s 



