Bats make good neighbors for Texas farmers, cities
A Bat Attitude
Each spring, billions of pests migrate north to Texas. Tobacco budworms and cotton bollworms--also called corn earworms--lay their eggs in crops, costing Texas growers more than $50 million a year.
Texas farmers spent $30 million a year from 1995 to 1997 trying to control these pest infestations through chemical applications and other techniques, according to John Westbrook with the U.S. Department of Agricultural Research Service.
The cost to Texas farmers would be much greater, however, without the aid of nature's crop dusters--Mexican free-tailed bats.
First line of defense
About 100 million Mexican free-tailed bats congregate in the Texas Hill Country each spring, giving Texas the largest concentration of these mammals in the world, Westbrook said.
When crop pests migrate to the south central Texas, also called the Winter Garden, the bats are ready for them.
"When these millions of corn earworms emerged from corn in the Rio Grande Valley, the winds were such that they could transport the moths from the lower Rio Grande Valley to the Winter Garden overnight," Westbrook said. "Working with the bat specialists, we learned the bats were already present in the Garden. The bats would consume these moths early in the morning, which were the ones coming in from a long distance and arriving in the early morning hours."
DNA testing and examination of the bats' guano show that crop pests are prevalent in the bats' diet, Westbrook said.
A study by Boston University Professor Cutler Cleveland estimated that farmers in the Winter Garden saved $741,000 per year thanks to the bats. The Winter Garden cotton harvest is worth about $6 million a year.
The savings are calculated by adding the value of the crop that would have been lost in the absence of the bats and the reduced cost of pesticide use, Westbrook said.
"There are still a significant number [of crop pests] migrating through San Angelo and Abilene, essentially up tornado alley with the prevailing winds," Westbrook said.
Pests that aren't killed early in their migration have a chance of increasing the damage and crop loss of North Texas and states further north, Westbrook added.
Worth their weight
"As we learn more, we are continually impressed with how economically and ecologically important [bats] are," said Merlin Tuttle, founder of Bat Conservation International (BCI).
During pest migrations, each female moth is carrying between 600 and 1,000 eggs, so if a bat eats half of its capacity, 20 moths, then one bat may be preventing the laying of up to 20,000 eggs, Tuttle said.
"Each lactating female bat consumes about 70 percent of its weight in insects in a single night, so the estimate is that 100 million Mexican free-tailed bats must consume over 1000 tons of insects per night while they are nursing their young," Westbrook said.
Carol Baxter, an apple grower in Medina, learned about the benefits of bats at a "bat party" hosted by friends. After listening to Tuttle describe the benefits of bats, the Baxters decided bats would make perfect neighbors.
"We put bat houses in our apple orchards because they eat the moths," Baxter said. She estimates there are 350 to 500 bats living in the six bat houses on their property.
"I certainly recommend it for anybody who has crops," Baxter said. "They're also wonderful to have around the house. We can sit outside without any bugs."
Frank Bibin, a pecan grower in Quitman, GA, attracted bats to his farm to cut back on insecticide use. In 1996, Bibin ran across a brochure by BCI on building a bat roost. Two years after he built his first roost, the bats moved in. He's built more than a roost a year since then, and now has 16 roosts placed strategically around his 24 acres of pecan trees.
"We're up to about 4,000 bats now," Bibin said.
Bibin said he spent about $400 in materials on each bat house, and he expects he'll break even in a few years.
"In the long term, it will save money because I don't have to deal with the insect problem," Bibin said. "Typically, when they spray the fungicide, they also spray the insecticide, which is pretty pricey."
The bats eliminate the need for the insecticide, Bibin said.
"We didn't like [using an insecticide] because our house was in the grove, and we felt the chemicals were really bad for the environment," Bibin said.
Bibin harvests the bat guano to supplement his fertilizer and is working on a way to use it in liquid form to spray on the trees.
"It'll go a lot farther that way," Bibin said. "The trees are able to absorb nitrogen better through their leaves. I haven't heard of anyone doing this yet, but hopefully, we'll get to that project next year."
Building in bats
In 1978, the Texas Department of Transportation (TxDOT) renovated the Congress Avenue bridge in Austin, accidentally making the crevices under the bridge the ideal size for bats, according to Mark Bloschock, head bridge designer for TxDOT.
A few years later, the bats began moving into the crevices. Today the bridge is home to 20 million bats and is the largest urban bat colony in the world, Tuttle said.
Now TxDOT tries to make most of its bridges bat-friendly, Bloschock said.
"Probably 100 percent of the time, if the bridge is in a rural area, we will do that," Bloschock said. It doesn't cost taxpayers a dime, he said.
"We take a design that we would already use and decide whether to make it suitable for bats," Bloschock said. "I'm unaware that we've built a bridge specifically for bat habitation that has cost us any more money than it would have cost anyway."
To the contrary, the Congress Avenue bridge adds about $8 million to the Austin economy each year. Tourists flock to the bridge to watch the bats emerge every evening to hunt, Tuttle said.
Once thought of as blood-sucking fiends that get tangled in hair and spread rabies, bats have a better rap now that organizations like BCI are dispelling common myths.
"There are a lot of misconceptions about bats," Tuttle said. "The one that does the most damage is people believing that most bats are rabid and going to attack them."
All mammals can contract rabies, but since the United States started mandating dog vaccinations, the disease has become extremely rare, Tuttle said.
"Bats are exceedingly unlikely to become aggressive even when sick," Tuttle said. "Sure, if you pick up and handle a sick bat, it might bite you in self-defense, but there's no reason to be bitten if you just leave them alone. You have to go pick one up, get bitten and then not do anything about it to die from rabies from a bat."
Fewer than two people in North America die from bat bites each year, Tuttle said.
"You're slightly more likely to be killed by having a soda machine fall on you than die from rabies from a bat," Tuttle said.