January 10, 2007
Skeeter Eaters of San Antone Posted by Frederic D. Schwarz at 04:50 PM EST I know it’s been a while since I’ve posted, but as my many dedicated fans will recall from this classic, I just can’t resist an item about bat guano. In this case, I was prompted by an article in the January 6 issue of The Economist (the issue date is listed as January 4 on the website, for some reason) about a professor who is studying the bat population in Texas. Bats are a great help to Texas farmers, eating large numbers of moths whose larvae infest cotton bolls. The article gives other examples of helpful bats eating agricultural pests in a wide-ranging group of states. Some farmers put up specially designed bat houses to attract more of the creatures (as do bridge builders, the article says, though it doesn’t say why).
The only thing that’s new here is that the attempts to lure bats may finally be working. A century ago, a Texas physician tried to do the same thing—not to protect agriculture, but to reduce malaria in humans. As explained in a 1982 article in our magazine, in 1902 Dr. Charles A. R. Campbell came up with the idea of luring insect-eating bats to places with large numbers of mosquitoes. The role of mosquitoes as vectors of malaria had recently been established, and Campbell hoped his scheme would reduce the disease’s prevalence. As a sideline, he planned to harvest the bats’ droppings for use as fertilizer.
When simple boxes scented with bat guano failed to attract any business, Campbell began building ever larger and more elaborate towers designed to accommodate hundreds of thousands of bats. He tramped through filthy, vermin-infested caves to see what sorts of architectural features bats liked most. Finally, in 1911, he opened “Dr. Campbell’s Malaria-Eradicating Guano-Producing Bat Roost” near a San Antonio sewage dump. Sure enough, malaria cases in the area dropped steeply.
Inquries streamed in from mosquito fighters around the world—“Russia, Greece, Japan, Australia, India, South Africa, and British Guyana,” according to the article. In 1914 Campbell received U.S. patent 1,083,318 on his bat-house design; by the early 1920s bat houses had been built across the South and in Mexico and Europe; and in 1925 Campbell published a book called Bats, Mosquitoes, and Dollars. (Contemporary photographs of Campbell’s bat houses can be seen here and here along with 1920s towers in Italy; a tower from the Florida Keys can be seen here, and a present-day restored bat tower can be viewed here, in case your copy of Bats magazine for Summer 1989 is not in a convenient place.)
The only problem was that Campbell’s bat towers didn’t actually work. Whether they succeeded in attracting bats is unclear, but even if they did, it didn’t help, because the ones that live in the San Antonio area are free-tailed bats. They eat moths, which makes them valuable to cotton farmers today, but they turn up their noses at mosquitoes. The decline in malaria cases was just a coincidence, caused by public-health education and the increased availability of cheap screening. By the time Campbell published his book, the value of the towers was coming into serious question, and at his death in 1931 he was close to forgotten, though his gravestone does have a copper plaque depicting a bat on it.
What does all this mean? Nothing, really. I just like to use the phrase “bat guano.”
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