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Bats stalking the night as new allies in mosquito fight

(MERLIN D. TUTTLE/ASSOCIATED PRESS/ BAT CONSERVATION INTERNATIONAL)

EAST BRIDGEWATER -- Health officials in this town of wetlands and woods are recruiting a new ally in their fight against mosquito-borne diseases -- an army of bats to scout the night skies and devour the insects.

Armed with research showing that bats eat 3,000 mosquito-size insects a night, the town put up 10 bat houses late last summer in places where mosquitoes seemed to swarm and bite the most: fishing holes, parks, and the East Bridgewater High School football field, where there's a house for 300 bats behind the scoreboard.

This summer the furry brown creatures, returning from their winter migration, took up lodging in some of the slender wooden boxes, sleeping away the daylight hours before their nightly feasting.

"When you think of bats, you think of vampires and issues of rabies and possible biting of residents," said Peter Spagone Jr., chairman of the East Bridgewater Board of Health, "but they are more afraid of us than we are of them."

The idea of using bats to fight mosquitoes and the diseases such as Eastern equine encephalitis they carry is popular in other parts of the country, and is starting to take flight around Eastern Massachusetts, as communities look for environmentally sensitive alternatives to chemical spraying.

The Plymouth County Sheriff's Office and Marshfield have put up bat houses, while other towns such as Plympton and West Bridgewater are considering it. Some homeowners have bat houses, too; it's not clear whether they are becoming popular.

Yet regional mosquito control boards and some biologists argue that mosquito-devouring bats are simply an old myth. Bats, especially the big brown and small brown species that are prevalent in the Bay State, prefer to dine on beetles, moths, or midges.

"In terms of suppressing the mosquito population, it's not a very good bet," said Thomas Kunz, director of Boston University's Center for Ecology and Conservation Biology, who plans to publish a scientific paper this fall debunking bats as a weapon against mosquitoes.

He said bats would prefer one large meal to having to hunt lots of small ones. "If you had a choice between one moth and 50 mosquitoes, you are probably going after the one moth."

Suburban towns are seeking other methods after a particularly aggressive round of spraying last summer, including the first aerial spraying in Massachusetts in 16 years last August. That led to widespread protests by environmentalists, who worried the chemicals would kill aquatic life, bees, and other bugs, while tainting crops of organic farmers.

But public health officials, who were supported by many residents, said they had no choice.

Mosquito-borne viruses, such as Eastern equine encephalitis and West Nile, are potentially deadly. EEE, since the outbreak began in 2004, has killed six people, including a 9-year-old Middleborough boy who collapsed during a football practice last August. West Nile has claimed six people since 2001.

Yesterday, health officials announced they had found the first mosquitoes infected with West Nile this summer, in Berkley in Southeastern Massachusetts.

So far this summer, however, drier weather has kept the mosquito population down along with requests for spraying. Still, local officials expect a surge in complaints in the coming weeks, the height of mosquito season. Last August, officials in many towns curtailed outside activities for youths at dusk, when swarms of mosquitoes thicken.

East Bridgewater first looked into enlisting bats two years ago after mosquitoes in town tested positive for EEE. Residents were initially skeptical, but Spagone emphasized that the town wasn't luring in bats: Bats already inhabited East Bridgewater. The town, he said, wanted to direct the winged mammal to areas buzzing the most with mosquitoes.

No bait is needed. Bats are drawn to the houses because the slim boxes are intended to simulate their natural habitat, such as crevices in dead trees, rocks, or eaves of houses. The boxes, about 28 inches long and 3 inches thick, are placed 18 feet high on a pole in an area where bats can see them. Inside, the bats hang upside down from mesh or cut grooves.

Bats are inhabiting four houses in East Bridgewater, with the highest occupancy 30 percent. Full occupancy takes about three years or more, and the houses can hold between 100 and 300 bats.

"How much will the bats bring down the mosquito population? I don't know," Spagone said. "We are still spraying, but if we can be environmentally smart and help citizens out, we should try out other methods."

Spagone said bats are a low-cost alternative, adding the 10 houses set the town back a total of $2,400. The town also is paying a local company, Atlantic Termite & Pest Control, $600 a year to monitor the houses, which were built by the Organization for Bat Conservation, a nonprofit in Michigan that works to protect bats and encourages using bats to control mosquito populations.

The state Department of Public Health, however, does not recommend the practice, saying it could bring rabid bats closer to people. The department prefers other safeguards, such as insect repellent, netting on baby carriages, and keeping birdbaths and other areas free of standing water, a breeding ground for mosquitoes. "Rabies is a serious disease," said Donna Rheaume, a public health spokeswoman. "One way to prevent it is not to come into contact with potentially rabid bats."

Last year, the department detected rabies in 4 percent of 756 bats that were submitted for testing. The Organization for Bat Conservation says that nationally less than 1 percent of bats test positive and argues that people would have a greater chance of falling down a flight of stairs or being struck by lightning than dying from a rabid bat bite.

As dusk approached one recent evening, people walking around an athletic track at East Bridgewater High School said they felt safer with the bats houses nearby. On this particular night, only one or two bats could be seen flickering among the trees beyond the football field, but there were plenty of swarming mosquitoes.

"Bats don't bother me, but mosquitoes do," said Michelle Morse, 34, an East Bridgewater mother of three. "They eat mosquitoes. That's better than spraying with chemicals."

James Vaznis can be reached at jvaznis@globe.com.

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