- Historic Sites
Dr. Campbell’s Remarkable Experiment
June/july 1982 | Volume 33, Issue 4
Quitting his medical practice for a time, he set up camp in the hill country outside San Antonio to study the interiors of two neighboring caves. They were nearly identical, but while one housed a large colony of bats, the other had none. A close comparative study, Campbell believed, would help him pinpoint the exact conditions necessary to lure bats to a tower. The work was arduous and thoroughly unpleasant: Campbell spent long hours cramped in observation, trudging through guano, choking on potent ammoniac gases in a fine rain of urine, while grotesque cave beetles and bats swarmed over him. But in the end Campbell was convinced he knew the decisive architectural features.
Returning jubilantly to San Antonio, he immediately secured a twentyfive-year lease on an acre of land near Mitchell’s Lake, a site selected for its ample endowment of malarial mosquitoes. Here his bat tower would have an exacting test. Into Mitchell’s Lake flowed the entire sewage of San Antonio—some ten to fifteen million gallons daily in 1910. While pasturage was rich in the area, the stock were perpetually emaciated from the mosquito attacks; the residents themselves were enfeebled by malaria. In one 1911 canvass, Dr. Campbell found seventy-eight of the eighty-seven people living on the lake shores to be infected with malaria.
On April 2, 1911, the second bat tower was completed. While Campbell referred to it simply as his Mitchell’s Lake roost, or affectionately as the “Hotel de Bat,” the large sign on its face proclaimed it to be “Dr. Campbell’s Malaria-Eradicating Guano-Producing Bat Roost.”
Constructed entirely of wood, the tower was thirty feet high and twelve feet wide at its base. Inside, it was intricately honeycombed to imitate a cave’s interior and divided into three distinct parts: a winter or hibernating roost; a summer roost; and a central open shaft that ran the entire height of the house, at the bottom of which was a funnel-shaped pit equipped with a trap door for the guano.
This time the bat tower was baited only with some guano and a “secret lure” that Campbell had developed. By August there were encouraging reports that the first bats had taken up residence. It soon became apparent, however, that the colony living in the tower was only a small fraction of the population Campbell had envisioned.
But the indefatigable doctor had meanwhile scouted a couple of abandoned buildings in the area that were homes for large colonies of free-tailed bats. He reasoned that bats, with their highly developed “hearing,” attuned to the tiny vibrations of mosquito wings, would be vulnerable to an attack by loud noises. Procuring a wagon, a phonograph, and a neighbor boy to crank the phonograph, Campbell left San Antonio on a fine summer morning. The expedition’s most valuable piece of equipment was a record, especially selected for its surfeit of blatant and shrill notes: the “Cascade of Roses Waltz” played by the Mexico City Police Band.
Within three days the bats had been driven from the abandoned buildings, and the majority of them took up residence in the tower. Campbell estimated the population at over two hundred and fifty thousand. Full colonization at last! Only time would now reveal if the bats were effective against malaria. Meanwhile Dr. Campbell began to promote his idea to all who would listen.
In 1913 a letter addressed to the “Bat Experiment Station, Texas, near Mexican Border,” arrived in San Antonio. It was from the Secretary of Agriculture of His Majesty’s Government in Rome, who wanted information about the tower. Campbell obligingly dispatched a full report, which was published in the monthly bulletin of. the International Institute of Agriculture in Rome. Shortly afterward the London Illustrated News published a picture of the Mitchell’s Lake tower, with a short description of its hygienic and economic value. Campbell began to receive inquiries from all over the world.
He received a U.S. patent on his bat tower in 1914. That year, duck hunters reported that the number of mosquitoes on the lake had so diminished that they could, tor the first time, remain in their blinds until dark. The malaria in the area appeared to have dropped dramatically. Campbell diligently procured witnessed affidavits from area residents testifying to the beneficial effects of the tower. On June 7 the San Antonio Express declared, “ … let it be known that the Campbell theory is no longer looked upon as impractical.”
In 1915 Campbell published an account of his bat research in Scientific American , and this brought another spate of inquiries from around the world. In 1917, responding to a letter writing campaign from San Antonio, the Texas State Legislature passed a bill making it a criminal offense to kill a bat in Texas.
In 1918 it was apparently accepted in San Antonio that the bat-tower idea was a success. There allegedly had not been a single case of malaria at Mitchell’s Lake for over two years. Campbell was now harvesting two tons of guano a year from his tower, which he sold to local flower growers for pin money. The Municipal Bat Roost was being credited with easing the malaria situation in the Mexican quarter. And this same year two other towers were constructed: by the State of Texas at the Southwestern Insane Asylum and on a private ranch near Comfort, Texas. In 1919 the city of Alamo Heights built the fifth and final tower to be constructed near San Antonio. This same year, by act of the Texas State Legislature, Campbell was nominated for the Nobel Prize.