ease common among the horses, cattle, and sheep of the Southwest. 

 The term "loco", as a definite common plant name, appears to have 

 been first applied to Astragalus mollwsiinus in western Texas, where 

 that plant was suspected of causing the disease known as locoism in 

 livestock, inducing craziness or stupefaction. Subsequently, a large 

 number of plants, chiefly of the genera Astragalus and Oxytropis, 

 have, at one time or another, been called loco, because of their poison- 

 ous effects on domestic animals. Although the early Spaniards 

 seemingly recognized the disease and symptoms, they were evidently 

 unfamiliar with the fact that the disease was caused by woolly loco, 

 because they named Astragalus nwllissimus garbanzilla from its re- 

 semblance to the chickpea, Spanish "garbano" (Cicer arietinum), 

 which is used in Spain as iood. The application of the term "loco" 

 to Astragalus mottissimus is no doubt relatively recent. 



The fact that woolly loco is poisonous has made the plant the 

 subject of considerable scientific study; consequently, its range is 

 known with noteworthy precision. It extends throughout the 

 southern plains region, being confined to the southwestern portion 

 of South Dakota, extreme southeastern Wyoming, the western half of 

 Nebraska, Kansas and Oklahoma, eastern Colorado, eastern Arizona, 

 New Mexico, northern Texas, and south into Mexico. The species 

 is most abundant in New Mexico and the Panhandle region of Texas. 



Woolly loco typically grows on the breezy, sun-drenched slopes of 

 the plains and prairies at elevations of from 4,000 to 6,000 feet above 

 sea level, occurring usually in small scattered patches, but occasion- 

 ally forming a moderate cover several acres in extent. It prefers 

 the heavy, clayey soils of the depressions and grows commonly on 

 heavy, sandy, or gravelly soils of the lower slopes, but seldom ap- 

 pears on ridges or elevated sites. Under favorable conditions, it 

 frequently attains a height of 1 to 2 feet, and a spread of 2 feet. 



Woolly loco is relatively unpalatable to all classes of livestock. 

 Under ordinary conditions, cattle will not eat the plant except in 

 dire hunger and neither horses nor sheep will partake readily of the 

 foliage except when forced to do so by the scarcity of better and 

 more succulent forage. However, Marsh et al. 1 state : 



It has been demonstrated that the so-called loco disease of the Plains is not 

 simply a matter of starvation, as many have supposed, though it is also clear 

 that when other feed is abundant very few horses will eat loco. 



If animals once begin to eat woolly loco, they are likely to form a 

 habit similar to the drug habit, or narcotic craving in man, and 

 when they become accustomed to graze the plant, they often consume 

 great quantities with special avidity. Frequently, all livestock, but 

 particularly horses, develop such a strong appetite for the herbage, 

 that they cannot be induced to feed upon any other forage as long 

 as woolly loco is available. Animals which continually consume this 

 poisonous pest usually become locoed and finally die. 



Woolly loco is one of the first range plants to become green in the 

 spring. During the early growing season, the species is especially 

 dangerous and constitutes a serious menace, because very little other 

 succulent forage is then available. Throughout the late spring and 



1 Marsh, C. D., Clawson, A. B., and Eggleston, W. W. THE LOCO-WEED DISEASE. TJ. S. 

 Dept. Agr. Farmers' Bull. 1054, rev., 26 pp., illus. 1929. 



