Vampire Bats: Myths vs. Facts
By Mary-Love Bigony, University Marketing
Vampires play a starring role in oral traditions, literature and films. They rise from their coffins at night to seek their victims. They defy death by sucking the blood of living humans, who then become vampires themselves. A vampire will die only if someone drives a stake through its heart or if it is exposed to sunlight. Such legends date back at least 4,000 years.
But the animals named for this classic fiend — vampire bats — are not nearly as sinister. They are about the size of a human thumb and weigh about as much as a AA battery. They spend their lives in caves and hollow trees from Mexico to South America. And in a few decades, they may be headed for Texas.
“Vampire bats are highly limited by temperature,” says Dr. Ivan Castro-Arellano, an assistant professor in Texas State’s biology department. “They cannot live in a place where temperatures drop below 50 degrees Fahrenheit. So their range, the area where they occur, might extend north across the Rio Grande if South Texas winters become warmer.”
Castro-Arellano conducts research on the ecology of wildlife diseases. “Diseases that occur in wildlife, or diseases that can jump from wildlife to humans, are part of my research,” he says. “I recently started working with collaborators in northeastern Mexico on vampire bat research, because vampire bats can be a disease vector. They have the possibility of transmitting rabies.”
Since the notion of vampire bats heading for Texas hit the media in early 2012, Castro-Arellano has become the resident expert on the blood-feeding mammals and has given dozens of interviews.
In summer 2012, Castro-Arellano traveled to Washington, D.C., as part of the United States Department of Agriculture’s E. Kika De La Garza Fellowship Program. He is the first Texas State faculty member to participate in the program, which offers faculty and staff from Hispanic Serving Institutions the opportunity to work collaboratively with the USDA to identify mutual collaborative interests.
Unlike movie vampires, vampire bats don’t suck blood. They use their razor-sharp front teeth to pierce the skin of cattle, pigs, horses and other mammals and lap it up. Castro-Arellano points out the differences between vampire bats and Mexican free-tailed bats, which migrate to Central Texas in the summer and are known for their voracious appetites for mosquitoes and other insects.
“The free-tailed bats are insectivores. They tend to fly higher. They are high-speed and long-distance fliers,” he says. “Vampire bats are short-distance fliers. They can go about 25 miles or so, but they tend to stick to an area close to their roost and they roost in smaller groups — 15 to 20 individuals usually. Free-tailed bats can occur in the thousands or even millions at their roosts.”
Vampire bats are the only mammals that feed entirely on blood. But contrary to the image of a huge beast with blood dripping from its fangs, the common vampire bat weighs only half an ounce to an ounce and a half.
“This is a fantastic animal,” says Castro-Arellano, “a fantastic research subject.”
Castro-Arellano couldn’t have anticipated becoming a vampire bat expert when he was growing up in Mexico City and Culiacán, on Mexico’s west coast. He developed a love for nature on camping trips with his father.
“Although we lived in a large city, my father took me camping from a very young age and I have always loved being afield,” he says. “Also, I had my first aquarium and my first hamster by age 6. By age 12, I had already bred several species of common tropical fish, which I later traded at pet shops for more expensive fish.”
He also developed a love for fishing and hunting, and as a teenager, saved money to buy The Wildlife of Mexico by Aldo Starker Leopold. “After finishing it I knew I wanted to be like the author of this book,” he says. “He was a professor at the University of California, Berkeley for a long time and even was elected to the National Academy of Sciences.”
Castro-Arellano earned his bachelor’s degree in biology from the National Autonomous University of Mexico, and his master’s and doctorate in wildlife ecology from Texas A&M. After serving as a postdoctoral fellow at the University of Connecticut, he returned to Mexico as an assistant professor at Instituto Tecnológico de Ciudad Victoria. There, Castro-Arellano worked with Dr. Arnulfo Moreno-Valdez, a professor at the institute and director of the Museum of Natural History of Tamaulipas. The two had been graduate students together at Texas A&M.
“We developed a project to look at the activity patterns of several bat species, looking at how the activity of the vampire bats overlaps with the activity of other bat species,” Castro-Arellano says. “Dr. Moreno-Valdez had raised this idea before, but had not been able to advance it. But now, with an algorithm that I developed, we can test those ideas. So that’s how I got drawn into this research.”
Here Come the Vampire Bats... Maybe
Currently, the farthest north that vampire bats are found is about 300 miles south of the Texas-Mexico border. While the bats’ metabolism prevents them from withstanding temperatures below 50 degrees Fahrenheit, some climate change models predict rising temperatures in the higher latitudes, Castro-Arellano says.
“What the models do is predict the distribution of the species based on the temperature,” he says. “Computer modeling shows a high probability — if the temperature predictions are true — that in about 50 years or so, these animals might be present here.”
Castro-Arellano and Moreno-Valdez are seeking funding for further vampire bat research.
“If we get the funding, one thing we could do is go to South Texas and start putting data loggers in certain places where we believe the animals might be roosting and monitor them for several years,” Castro-Arellano says. “And if we find that inside those roosts temperatures never fall below 50 degrees Fahrenheit, then we start thinking that there might be a higher likelihood in the future for vampire bats to occur.”
And if they do start showing up in Texas?
“The biggest concern is the economic impact they could have,” says Castro-Arellano. “When a vampire bat finds an animal it can feed on, like a donkey, a horse or a cow, the bat tends to return to the same animal night after night.
“The other concern would be the diseases they bring, including rabies,” he continues. “I need to emphasize most vampire bat do not have rabies, but a few of them will. Because of their mode of feeding, a vampire bat with rabies would be more likely to transmit it than other bat species. But since they occur in such low numbers, their effect is highly localized and they can be managed.”
He adds that vampire bats seldom feed on humans. “It could happen,” he says, “but it would be extremely rare.”
Castro-Arellano says that vampire bats’ unusual feeding technique led to the development of anticoagulant drugs used to prevent embolisms, heart attacks and strokes. Research on the chemical in the bat saliva has provided a drug with benefits for humans.
“When these animals bite their prey, they can’t have the blood clot,” he says. “So they have an anticoagulant in their saliva to keep the blood flowing.”
He emphasizes that if vampire bats do show up in Texas, biologists will be able to manage them easily without harming beneficial bats.
“People should not harm any bat, because the layperson can’t tell a vampire bat from a beneficial bat,” he says. “People shouldn’t be scared. We need to be prepared, and that’s why we’re starting investigations early.”