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Bats Enlisted to Gobble Up Earworm Pests

By Linda McGraw
May 5, 1999

In early June, billions of corn earworm moths emerge from the Lower Rio Grande Valley along the border of Texas and Mexico. Some moths feed on cotton after leaving southern corn, while others travel north to ravage midwestern corn crops. Each year, these pests cost farmers about $2 billion in losses and control costs.

To control the moths, Agricultural Research Service scientists in College Station, Texas, are capitalizing on the voracious appetite of Mexican free-tailed bats. Corn earworm moths are one of the bats’ favorite foods. A million bats can gobble up nearly 10 tons of insects in just one night. So the 20 million bats living in Bracken Cave near San Antonio, Texas, could put a real dent in moth populations.

ARS meteorologist John K. Westbrook, who has studied moth migration for 17 years, knows that bats and moths typically fly at about the same altitude. His collaborative work with bat specialist Gary F. McCracken of the University of Tennessee and Merlin Tuttle of Bat Conservation International is secondary to his main interest: moth migration.

To confirm the bats’ appetite for moths, Westbrook attached radiomicrophones to helium-filled balloons called tetroons. While the tetroons drifted at an altitude of about 2,500 feet, the researchers could hear and record the high-frequency sounds of bats searching for and feeding on moths.

The National Weather Service’s Doppler radar system (NEXRAD) helps the researchers detect masses of moths more than 60 miles away from a radar site, one of which is located in Brownsville, Texas. Like firefighters putting out the “hot spots” first, the NEXRAD radar research may be used to develop time-critical maps to help control moth infestations over a large area.

ARS’ Areawide Pest Management Research in College Station has one of the most active radar-entomology research programs in the world. An article about the research appears on the May issue of Agricultural Research magazine and can be found on the world wide web at:


ARS is the USDA’s chief research agency.

Scientific contact: John K. Westbrook, ARS Areawide Pest Management Research Unit, College Station, Texas, phone (409) 260-9351, fax (409) 260-9386,