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July 2024
8min read

Dr. Campbell’s Remarkable Experiment

n the last issue we told how the United States in World War II attempted to bring destruction to Japanese cities by peppering them with bomb-carrying bats. Bizarre though that experiment sounds, it was not the first time the Americans tried to enlist the help of bats. Herewith, the strange tale of Dr. Campbell’s lifelong obsession.

The story of the bat towers, large wooden structures designed to garrison colonies of bat “soldiers” in the war on malaria, may sound like a tall Texas tale. But the towers were real. A few even remain standing today.

When Dr. Charles A. R. Campbell graduated from Tulane Medical School in 1899, he returned to his native San Antonio to specialize in the treatment of malaria, then a terrible problem throughout the South. Campbell had been greatly excited by recent proof that the mosquito was the disease’s vector. Now, with the enemy a well-identified foe instead of a vague “miasma,” a new age of combating malaria had begun. As early as 1900 Dr. Campbell began to consider using bats.

Mosquito control was still an infant science at the turn of the century: crude metallic poisons were dumped into breeding sites, and corn oil, cactus paste, or petroleum products were spread over the surface of waters.

The idea of drafting bats was perhaps not as bizarre as it now seems. As early as the 1850’s English sparrows were introduced into the Northeast to fight insect populations in growing urban areas. The introduction of the Vedalia beetle into California in the 1880’s to combat the cottony-cushion scale menacing citrus groves had been an outstanding success. Even while Campbell was developing his scheme, there were researchers scouring distant parts of the world to find the natural predators of such banes to American agriculture as the gypsy moth, the brown-tail moth, and the sugar-cane leaf hopper.

Campbell knew of this work yet felt there was no need to send agents to remote lands when, “in the little bat, we have right at home a friend whose wonderful habits we can take advantage of in the saving of precious human lives.”

The burning question that occupied Dr. Campbell’s mind after 1900 was, Could bats, like bees, be colonized and made to multiply in strategic locations? In 1902 he began a series of experiments with boxes scented with bat guano, which he placed in trees, under country bridges, in large warehouses, in livery stables, and even on his front porch. The experiments were all failures: none of his boxes attracted bats.

Disappointment spurred Campbell to begin a study of the numerous caves in the area. Many of these bat caves had a long history of profitable trade in guano, which had been used during the Civil War to make saltpeter for gunpowder. Since the war it had been sold for fertilizer. Most of the caves contained over a million bats and produced over sixty tons of guano a year.

Impressed with the size of the bat colonies and with the fact that their guano production was so lucrative, Dr. Campbell brought a new element to his scheme. He began to dream of great towers, containing hundreds of thousands of bats each, which not only would control malarial mosquitoes but also would have a commercial element to encourage their construction. Bats for health and healthy profit; bats converting mosquitoes into dollars.

The world’s first bat tower went up in 1909. Dr. Campbell had by this time so neglected his medical practice that he needed to borrow money from a friend to pay for its construction. The cost was five hundred dollars; the site was a small corner of the U.S. Department of Agriculture experimental farm some six miles south of San Antonio.

To attract bats Campbell seeded the tower with guano and, inside, hung several smoked hams. Outside he stacked several cords of mesquite wood and erected a night lantern on a post—both measures to attract insects. Finally he placed several barrels of water nearby to serve as breeding tanks for mosquitoes. Weeks, then months, passed. The tanks produced so many mosquitoes that he was requested to remove them from the farm. No bats came to his tower.

As a last-ditch effort, Campbell spent two hundred and sixty dollars remodeling the interior of the tower in the spring of 1910. He had recently observed that at the deserted main exhibition building of the old fairgrounds just a mile away, there was a large colony of bats. Now, through the good offices of the mayor of San Antonio, Dr. Campbell had a fire department hose company placed at his disposal. Throughout one day, the firemen fought the bats with streams of water in an attempt to get them to relocate in Campbell’s tower. The panicked bats, however, merely circled clamorously from one part of the building to another.

The failure of this first tower seems to have affected Dr. Campbell deeply. In his memoirs he describes how he afterward “racked his brain, spending many sleepless nights, planning, pondering … even dreaming over this most vital of all problems, colonization.” Surely, he felt, there must be some way. “Was the solution to the problem that meant so much to humanity, to countless millions yet unborn, to go unsolved?”

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.

In the early 1920’s bat towers appeared in Tampa, Florida, and in Gulfport, Mississippi. During this period, towers may (P*^ also have been constructed in the Tampico oil fields of Mexico and in the Belgian colonies, and from Campbell’s correspondence it is certain that the idea was also known in Russia, Greece, Japan, Australia, India, South Africa, and British Guyana.

In 1925 Campbell published an account of his work called Bats, Mosquitoes and Dollars , which got favorable reviews in New York newspapers and apparently enjoyed wide sales. Nevertheless, certain ominous signs had appeared, and the end was in sight.

A growing number of articles appeared which claimed that the battower idea was essentially a hoax. The first to cast doubt was Dr. L. O. Howard, Chief of the Bureau of Entomology of the U.S. Department of Agriculture. In a report in 1920 Howard stated that Campbell’s claims for the Mitchell’s Lake tower were greatly exaggerated: that there were only about nine thousand bats there instead of the quar- |j ter million that he claimed. Also, analysis of guano taken from nearby bat caves revealed that the Texas free-tailed bats subsisted almost entirely on moths. Nothing resembling mosquito remains was to be found in their guano.

In 1926—perhaps to counter Campbell’s publicity and the awakening of interest in the bat-tower idea stirred by the publication of Bats, Mosquitoes and Dollars —four other negative reports appeared. The particulars of the reports varied, but they were very clear on two crucial points: the Mitchell’s Lake bat tower was the only one to be successfully colonized, and free-tailed bats do not eat mosquitoes.

It is clear from later studies of free-tailed bats that their principal diet is lepidopterous insects. They rarely, if ever, eat mosquitoes. Even had Campbell’s towers been colonized, they would not have worked for malaria control.

And the bat towers could not have been colonized. Despite their large size, they were far too small to contain a normal Texas bat colony. They did not provide for rapid enough inflow and outflow. Above all, they were competing against a small number of select ancestral caves. Most of the towers attracted only small numbers of bats, and these only sporadically: roosting in buildings appears to be primarily a transitory “overflow” phenomenon. That the Mitchell’s Lake tower was successfully colonized can perhaps be attributed only to the “Cascade of Roses Waltz.”

Why then did San Antonio believe that bat towers were singlehandedly responsible for removing malaria from the city. Available statistics indicate that there was, indeed, a steady and dramatic decrease in the malaria rate during the period from 1903 to 1930. The bat towers got the credit, but the true cause appears to have been widespread public education about mosquito control and increased availability of cheap screening—the same factors that lowered malaria rates in many other places during the same period.

After Dr. CampbeH’s death in 1931, his son Milton continued for several years to sell “detailed plans” and the “secret lure” to prospective bat raisers. But few new towers were built. By the end of the 1920’s the caveat concerning bat towers appears to have become widely circulated. The expensive construction cost—about two thousand dollars by 1930—would have discouraged use of the idea for guano production alone.

The Texas law protecting bats was struck off the books during a revision of the state wildlife code in 1975. As far as can be determined, only two bat towers still remain standing: one near Comfort, Texas, on a private ranch; one near Sugarloaf Shores in the Florida Keys. In San Antonio, the tower idea’s native soil, the only remaining artifact of the phenomenon is a copper plaque depicting a bat on Dr. Campbell’s grave.

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