Every night, as the sun sets across Central Texas, an estimated 100 million bats take flight.
Sound scary? Not to farmers.
The nocturnal mammals feast on a smorgasbord of pests whose offspring devour corn and cotton plants. Crop damage from such pests -- and from chemicals to treat fields -- costs farmers $1 billion a year nationwide, said Gary F. McCracken, a bat researcher at the University of Tennessee.
"The bats really chow down on these moths in big numbers," said McCracken, who is studying the bats' impact on insects.
Bats can devour about 1,000 tons of insects each night in Texas, which has the nation's largest bat population and the world's largest single bat colony. The bat is the state's official flying mammal.
McCracken's study, in its second year, uses infrared thermal imaging cameras to get a more accurate count of bats in Central Texas. Other scientists will try to figure out how much of a bat's diet is composed of moths.
"This is very important work, and we're happy to see it taking place," said Barbara French, science officer with Austin-based Bat Conservation International, a nonprofit group that works to protect bats and their habitats.
Most of Texas's bats live within a 100-mile radius of San Antonio.
By eating the moths, bats prevent them from laying thousands of eggs, which grow up to become corn earworms and pink cotton bollworms that chomp through crop fields.
"That definitely translates into a dollar savings to the farmers," said Patricia Morton, a spokeswoman for the Texas Parks and Wildlife Department, which is part of the study.
Female bats, which have only one pup a year, migrate to Texas in March to munch on moths and feed their offspring. Each night, a mother bat gobbles down two-thirds of her body weight. Surviving adult moth generations migrate through Texas on their way to Midwest corn fields.
"So our bats in Texas are the front line," Morton said.
If the bats in Central Texas eat enough moths, there will be fewer heading north to the world's largest cotton patch, said James F. Leser, cotton entomologist with the Texas Cooperative Extension of the Texas A&M University system.
That could be good news for South Plains cotton farmers during late July, August and September, he said.
The research, funded by a $2.4 million National Science Foundation grant, took shape after mysterious large "clouds" appeared on National Weather Service radar in Central Texas in the early 1990s on otherwise clear days. The clouds turned out to be millions of bats.
Not long afterward, a weather service radar station in South Texas picked up more strange clouds intersecting with the bat clouds thousands of feet above ground. Researchers found the unknown clouds to be millions of migrating moths.
Watching black clouds of bats spiral out of caves is a popular spectator sport in Texas. Bracken Cave, north of San Antonio, is home to the world's largest bat colony, with an estimated 20 million bats. The Congress Avenue Bridge in Austin is the world's largest urban colony.