Skip to main content

KNOXVILLE, Tenn.– Numbers in the millions and billions slip off Dr. Gary McCracken’s tongue with the ease of an astronomer talking about stars in a galaxy.

 McCracken has his eye on the sky all right, but the skies he watches are over south-central Texas. The billions are corn ear moths and the millions are free-tail bats.

 A biologist at the University of Tennessee-Knoxville, McCracken has been studying the free-tail bat for the past three years in cooperation with the U.S. Department of Agriculture and authorities in Mexico.

 By the time McCracken finishes his research, he hopes more people will appreciate the free-tail bat’s role as a guardian of America’s food supply.

“I want to be able to say, ‘This is the dollar value of these bats. This is what they do for us and this is why we need to be concerned about their declining numbers,”‘ McCracken said.

 McCracken said the bats’ story begins every June when approximately 7 billion corn ear moths take flight from Mexico and points further south.

 “In a single night they can travel 200 miles into the Winter Garden region near San Antonio,” McCracken said.

 Thousands of feet above the Winter Garden’s fields of cotton, corn, tomatoes and other crops, the moth migration is met head-on by millions of free-tail bats, McCracken said.

“We knew the bats were up there and the moths were up there and that bats like moths, but we needed to document the bats were feeding on the moths,” McCracken said.

 Prior to McCracken’s work, most studies of bat feeding habits were made at low level — less than 100 feet — because that was the limit of sound detection devices used to monitor bat activity.

 “Bats emit a high frequency call that we can use to tell what type of bat they are, how many there are, and whether they are approaching or feeding on insects,” McCracken said.

 Two years ago McCracken followed the bats by piggybacking sound detection devices on balloons. This year he used smaller versions of the listening devices mounted on high-altitude kites developed at the University of Colorado.

 “The beauty of the kites was that they allowed us to place our microphones at different altitudes up to several thousand feet,” McCracken said.

 The listening devices helped McCracken document the small bats’ big appetites.

“Multiply the number of bats by what they eat — it comes to approximately 2.5 million tons of insects per night,” McCracken said. “That’s trainloads and trainloads of insects.”

 The bats’ appetite directly benefits American farmers because surviving female corn ear moths will each lay a 1,000 or more eggs in a few days. The resulting larvae destroy or damage a variety of crops, McCracken said.

 “Each generation gets larger and larger as they hopscotch across the continent,” McCracken said. “The moths are the United States #1 agricultural pest. They do $1 billion a year in damage.”


 Contact: Dr. Gary McCracken (423-974-6041)