A secret war is waged above farmland every night. Just after dusk, high-stakes aerial combat is fought in the darkness atop the crop canopy. Nature’s air force arrives in waves over crop fields, sometimes flying in from 30 miles away. Bat colonies blanket the air with echo location clicks and dive toward insect prey at up to 60 mph. In games of hide-and-seek between bats and crop pests, the bats always win, and the victories are worth billions of dollars to U.S. agriculture. Bats are a precious, but unheralded friend of farmers, providing consistent crop protection. Take away the colonies of pest killers and insect control costs would explode across farmland. And just how much do bats save agriculture in pesticide use? Globally, the tally may reach a numbing $53 billion per year, according to estimates from the University of Pretoria, U.S. Geological Survey (USGS), University of Tennessee, and Boston University.
A 2006 study proposed bats saved cotton growers $74 per acre in pesticide treatments across eight Texas counties. In 2013-2014, graduate student Josiah Maines and his advisor at Southern Illinois University Carbondale, Justin Boyles, went beyond penciled estimates and ran a concrete field trial to show the relation between bats and corn protection. Funded by Bat Conservation International, Maines’ unique test targeted density of corn earworm in southern Illinois bottomland in Alexander County. Maines built a canopy system to prevent bats from accessing particular sections of corn at night. The controlled enclosure (65’ by 65’, and 23’ high) was braced by steel structural poles interconnected with steel cables draped by netting. Maines operated the netting like a gigantic shower curtain every day of crop season: Open in daylight and close at night. He kept the vigil over two years, sliding the big curtain at the given dusk hour from May to late September to cut off bat access to earworm moths. The results? Maines was astonished. He found a 50% reduction in earworm presence in control areas and a similar reduction in damage to corn ears. Not only did bats suppress earworm larvae and direct damage to corn, they also hindered the presence of fungal species and toxic compounds. “Globally, we estimate bats save corn farmers over $1 billion annually in earworm control,” Maines says. “It’s an incredible amount when we’re only considering one pest and one crop. Bats are truly a vital economic species.” Would producers see greater crop protection with more bat habitat? In general, researchers don’t know how many bats fly over a single acre of farmland at night. Bats are extremely difficult to count during the day. They hide incredibly well in trees, caves, holes in the ground, and buildings. “Future research should look at the tradeoff of forested bat habitat and crop protection. Safe to say, more bats could mean even greater consumption of crop pests,” Maines says. Paul Cryan, a USGS research biologist at the Fort Collins Science Center, says of up to 45 bat species in the U.S., 41 to 42 eat nothing but insects. “Our U.S. bats are small -- 10 to 20 grams. They have voracious appetites and eat half or all their body weight each night. Pest control value to agriculture is certainly in the billions of dollars per year.” However, pressing issues surround the future of U.S. bat populations. White nose syndrome (WNS) is a major threat to U.S. bat numbers. The fungal disease affects hibernating bats and has spread halfway across the U.S. since first appearing in New York in 2006. “WNS has killed up to 6 million bats and continues moving,” Cryan says. “I believe farmers would see an immediate impact in insect suppression if overall bat populations were seriously reduced.” Cryan coauthored a seminal 2011 paper, Economic Importance of Bats in Agriculture, suggesting the loss of bats would cost U.S. agriculture at least $3.7 billion per year. “We’re typically scared of the dark, but bats shouldn’t be a part of that association. They’re such a beneficial and important part of the environment and farmland protection.” Hat tip to the misunderstood bats of agriculture: phenomenal creatures patrolling farmland skies every night in the greatest show never seen.