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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.