2 BULLETIN 1395, U. S. DEPARTMENT OF AGRICULTURE 



habits of one species may not apply to others of the same or distant 

 localities. Generalizations from one species can not be safely ap- 

 plied to others without a full knowledge of their habits. Certain 

 bats of highly colonial habits are found in the Tropics and across 

 the southern United States, limited mainly to the southern parts 

 of these States, but these colonial habits do not apply generally 

 to the more northern bats and by no means to all species in the 

 South. This bulletin discusses the relation of colonial bats to the 

 production of guano and the destruction of insects. 2 



THE MEXICAN FREE-TAILED BAT 



Most of the sensational reports of discoveries of a great commer- 

 cial value of bats as well as of sanitary benefits from their presence 

 have been based on one species occurring in southern Texas, the 

 Mexican free-tailed bat, Tadarida mexicatia, long known in litera- 

 ture as Nyctinomus mexicanus, and belonging to the mainly tropical 

 family Molossidae. In tropical and subtropical America, the West 

 Indies, southern Europe, eastern Africa, southern Asia, Australia, 



Pig. 1.— Mexican free-tailed bat {Tadarida mencana>. a small soot> -hi m\n mam- 

 mal with a wing spread of about 12 Inches; habitant of Mexico ^d the arid 



Southwest, and the? only species in the United States known to produce guano 

 in commercial quantity 



and many islands of the Pacific there are about 40 species of the 

 genus Tadarida, but only 4 of these reach northward into southern 

 United States, and only 1 is known from southern Texas. 



The range of bats of the species Tadarida mexicana is in general 

 restricted to the arid and semiarid sections of the Lower Austral 

 Zone in the United States from Texas to California, and extends 

 also throughout most of the warmer parts of Mexico. The north- 

 ward limit of their range is apparently fixed by temperature or 

 suitable food supply, and the eastward perhaps by the presence 

 of a related species. 'Tadarida cynocepliala, with very similar habits 

 but occupying the humid division of the Lower Austral Zone from 

 southern Louisiana to Florida and South Carolina Two closely 



related forms Tadarida femoromcca and Tadarida depressa, are oi 

 rare occurrence in the Southwestern States. 



The Mexican free-tailed bats are small, sooty-brown mammals 



spreading about 12 inches across extended wings, with projecting 



2 While this bulletin was in press a volume just published, by Charles A. R. Campbell, 

 "Bats! MoSquitoel! TtdDJSw? was received. The book does not in any way alter 

 the conclusions as set forth in these pages. 



