BATS IN RELATION TO GUANO AND INSECTS 11 



were swarming about the houses, these bats were living in the roof- 

 in great numbers, apparently without having the slightest influence 

 on the numbers of the mosquitoes. At one large cave, water in the 

 entrance afforded a breeding place for mosquitoes, which were pres- 

 ent in such numbers as to cause great annoyance in efforts to collect 

 some of the bats for scientific specimens. 



The assertions of Doctor Campbell that bats feed very extensively 

 on mosquitoes, practically eliminating them in the vicinity of bat 

 roosts and thus effectively preventing malaria, have been followed 

 with interest by entomologists of the Department of Agriculture, 

 and all evidence carefully weighed by Doctor Howard 5 in his paper 

 on the subject. He has* written the following two paragraphs for 

 insertion in this bulletin : 



''After a prolonged effort I have been unable to substantiate the 

 claims made by Doctor Campbell as to the value of bat roosts in 

 the great reduction of the mosquito population of a given locality, 

 even in Texas. Bats obviously prefer other and larger insects. 

 The}' undoubtedly swallow mosquitoes when they encounter them in 

 flight, but only incidentally. Observations by trained men on the 

 ground in Texas deny his claims both as to marked relief from 

 mosquitoes or relief from malaria. One of the experts of the Bureau 

 of Entomology stationed at San Antonio informs me (May. 1925) 

 that of the four bat roosts at San Antonio only one is inhabited by 

 bats, and that in endeavoring to watch the flight of the bats from 

 this roost in the evening he was so annoyed by mosquitoes that he 

 was obliged to abandon his observations. He further tells me that a 

 Mexican, resident 300 yards from the roost, states that the mos- 

 quitoes are very bad at his house. 



"As to other parts of the world, I am told by no less authority 

 than Professor Grassi that in Italy the most malarious regions are 

 precisely those where bats are most abundant.'* 



SUMMARY 



Xearly all the bats of Xorth America north of the Tropics con- 

 sume vast quantities of insects, but apparently do not exterminate 

 any. In evaluating their services as insect destroyers it is to be 

 borne in mind that they feed almost entirely on night-flying species. 



The Mexican free-tailed bat, ranging in the United States in 

 southern Texas. New Mexico, Arizona, and California, is extremely 

 colonial in habits, occupying numerous caves and some buildings, and 

 producing in places sufficient quantities of guano to be used com- 

 mercially as fertilizer. 



The possibility of colonizing these bats by building suitable roosts 

 has been demonstrated in the United States, but in only one instance. 

 Many difficulties are likely to be encountered in establishing colonies. 

 Elaborate and expensive structures built outside the range of a 

 colonial species or in places where the bats of the locality find other 

 quarters preferable may not be occupied. Unless the bats can be 

 attracted in large numbers, there is little hope of establishing a 



c Op. cit. 



