Murciélagos pueden controlar Mosquitos y Residuos pueden servir de Fertilizante

http://www.shorpy.com/node/1944
1914. Dr. Charles Campbell and a "municipal bat-roost" in San Antonio, Texas ("for one of man's best friends"), his idea for mosquito control at a time when malaria was a major public health problem in the U.S. Disguised as a favorite bat habitat — a church steeple, complete with cross — the roost was fitted with a trapdoor and stilts to facilitate the harvesting of guano by the wagonload for use as fertilizer. George Grantham Bain Collection.