Would Releasing Thousands of Bats in Miami Kill Off Zika-Carrying Mosquitoes?

Miami-Dade County Mosquito Control experts are struggling to contain the Aedes aegypti mosquito, which brought the Zika virus to Wynwood this week. Workers are frantically treating open water in the area, and planes will soon spray the neighborhood. Despite all of that, a 15th locally transmitted case of the disease was reported yesterday.

"They've been applying both chemicals that kill larval mosquitoes and adult mosquitoes every day," Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, told CBS News. "It isn't working as well as we had hoped." 

With mosquito control experts stretched thin, some residents have already demanded the county get creative. Could flooding the city with mosquito-hungry bats be one option?

Bats are, famously, one of the mosquito's natural predators. According to some experts, a single brown bat can gobble up to 1,000 mosquitoes in a single hour. So if the county released a cave's worth of bats into the Wynwood sky every day, Miami's mosquito problem would be eradicated in a fortnight, right?

Turns out the idea isn't all that crazy: Last month, the New York Times chronicled suburban North Hempstead, New York's plan to build "bat houses" — which look and function like bird houses except with slot-shaped holes for bats — across its Long Island town. According to one mosquito expert the Times quoted, bats burn so many calories through flying that they pretty much have to inhale mosquitoes indiscriminately to keep themselves full.

But town officials say it's impossible to quantify what impact the bats have had, and Laura Finn, a Central Florida bat conservation expert who spoke with New Times via phone, says she doubts they would be able to wipe out mosquitoes on their own.

"I certainly wouldn’t say don’t do it," Finn tells New Times. "I think it’s a good thing. They won’t solve the problem, but they do contribute to reducing the numbers. Without bats, everything would be worse."

But, she says, because bats alone wouldn't kill enough mosquitoes, pest control experts would still need to use pesticides to smoke out the Aedes aegypti. This, she says, could end up poisoning any new bats brought into the area.

"If you rely on spraying," she says, "it becomes kind of a vicious cycle."

That being said, she predicts the bats would still have a small impact, and encourages area residents to build more bat houses to attract more bats to the area. "I always recommend installing bat houses if you’ve got issues you need some help with" she says. "The bat houses keep them doing the good stuff and keep them from causing inadvertent problems," such as spreading their own diseases.

Two Miami-Dade Mosquito Control spokespeople, who are understandably quite busy this week, did not respond to New Times' requests to chat about bats.

But elsewhere, the Austin, Texas-based Bat Conservation International apparently received so many Zika-related questions this year that it released its own fact sheet about bats and mosquitoes in July.

The main problem, the group says, is that, although bats eat mosquitoes, the Aedes aegypti strain tends to be most active during the day, when most bats are presumably asleep.

"With these mosquitoes being most active just during dusk or dawn, it is a bit unrealistic to rely on bats to prevent the risk of the Zika virus," Winfred Frick, the group's senior director of conservation science, said in a statement.

If anything, she added, increased pesticide spraying would have "very dire impacts" on any bats that already live in the area.
Finn, meanwhile, says there's another obvious problem with releasing thousands of bats into the sky: They'd all just fly away.

"It would be great if the bats would stay," she says. "But you can't move them like you can with bees. They're just going to fly back to where they came from. They've got a really good homing instinct."
Update: A number of intrepid readers have pointed out that Sugarloaf Key, Florida, actually tried this exact technique in 1929. According to the Atlantic, Sugarloaf real-estate developer Richard Clyde Perky constructed a 30-foot bat tower at the end of the key in order to clear out mosquitoes in the area. Despite loading the tower with pheromone-soaked bat guano (poop), not a single bat ever moved into the gigantic, creepy looking bat hotel.

The tower, however, now sits on the National Register of Historic Places.

Correction: This piece previously misstated one of the founders of Bat Conservation International.