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MEMORANDUM CONCERNING THE USEFULNESS OF BATS AS DESTROYERS OP 

 MALARIA-CARRYING MOSQUITOES. 



The matter of the usefulness of bats in the destruction of mosquitoes has 

 been greatly exaggerated by the newspaper exploitation of Dr. Campbell's 

 experiments near San Antonio, Texas. All of these articles, as well as Dr. 

 Campbell's statement of his case, which I have read in full detail, appear 

 to ignore the fact that there are many species of bats (each with its peculiar 

 geographic distribution) with greatly varying habits. Only extremely few 

 species gather in large numbers to roost. Among these the species inhabiting 

 Dr. Campbell's artificial roost near San Antonio is perhaps the most gre- 

 garious of all. The bat on which Dr. Campbell is experimenting is Nycti- 

 nomus mexicanns, a small free-tailed bat of wide distribution along the 

 southern border of the United States and thence southward through Mexico 

 and the tropics. These bats commonly roost in very great numbers in dry 

 caves, about the roofs of houses, gables of churches and similar places. They 

 swarm out at night and fly over many miles of territory, not concentrating 

 their hunt for food in definite areas as would be necessary to clean up the 

 mosquitoes. Furthermore, examination of the food contents of the stomachs 

 and excrement of these bats, while showing that mosquitoes are eaten by 

 them, fails to show that these insects form any considerable part of their 

 food. 



I spent some years studying the birds and mammals of Mexico and lived a 

 large part of that time in places where these bats are extremely abundant. 

 Their presence in no case appeared to have the slightest influence on the 

 prevalence of malaria. I have lived in many Mexican villages and ranches 

 where malarial mosquitoes were swarming about the house while these bats 

 were living in the roofs in great numbers, apparently without having the 

 slightest influence on the number of mosquitoes present. 



I have seen Dr. Campbell's statement of his case in regard to the supposed 

 benefit from his bat roost to the city of San Antonio. It appears evident that 

 he fails to appreciate the fact that there are a considerable number of different 

 species of bats living in the vicinity of San Antonio and which may be seen 

 flying about in company with the species which inhabits his roost. I doubt 

 if he has given the food habits of these animals sufficiently close scientific 

 study. Owing to the popular appeal of his experiment and to his positive 

 statements of results his plan has received widespread and unwarranted news- 

 paper notoriety. 



As already stated, bats have distinct geographic ranges commonly limited 

 by climatic conditions. The bats from northern localities either migrate to 

 warmer climates during the winter or hibernate in caves, hollow trees or 

 similar sheltered places. The bats from the northern States would certainly 

 not colonize and remain permanently in the South. Neither would the bats 

 which inhabit Dr. Campbell's bat roost remain in the North beyond their 

 climatic range. These bats belong to the Lower Sonoran and Tropical 

 Zones. It is probable that within proper climatic conditions the bat being 

 experimented upon by Dr. Campbell might be colonized by building similar 

 roosts or shelters to those he employs and wetting the interior with a solu- 



