A common saw on the worth of bats is human-centric: They eat bugs.

A bat, in a single night, will eat half of its weight in insects — not just the mosquitoes that plague us but all manner of night flyers, like moths and beetles.

Some researchers have gone to great lengths to measure this worth in economic terms. But the dollars and cents aren’t why Carl Herzog cares about bats. He’s a biologist with the Wildlife Diversity Section of the state’s Department of Environmental Conservation.

“Bats are the number-one consumer of flying insects at night,” he said. “That’s the main ecological function, how they fit into the web of life…It’s the big reason most people care about bats. But some people think, because they’re here, it’s our responsibility to take care of them.”

Herzog is one of those people. His personal philosophy is rooted in the work of Aldo Leopold, whom he described as the father of wildlife conservation. He summarized one of Leopold’s chief tenets this way: The first rule of intelligent tinkering is not to throw away any of the parts.

Leopold had written in Round River, published in 1953, five years after his death, “The last word in ignorance is the man who says of an animal or plant, ‘What good is it?’ If the land mechanism as a whole is good, then every part is good, whether we understand it or not. If the biota, in the course of aeons, has built something we like but do not understand, then who but a fool would discard seemingly useless parts? To keep every cog and wheel is the first precaution of intelligent tinkering.”

“We don’t understand the interaction all that well,” Herzog said of bats to their environment. “It’s so complicated, it may not be possible to understand.”

Herzog worked for two decades as an electronics engineer and felt he had met his financial obligations — his child had gone to college and was on her own — when he pursued his passion. In what he described as a mid-life crisis, he went back to school, for a master’s degree from Prescott College in Arizona, since he had spent countless hours studying wildlife on his own. A state job wasn’t his goal but he finds serving the public to be rewarding.

As a wildlife biologist, he now coordinates all the bat-related work for the state. New York is home to nine different species of bats — six are bats that winter over in New York caves or mines while three species fly south in the winter.

The most common is the big brown bat, which frequently spends the warm months in attics or barns and lives in colonies. The little brown bat may be the best known since, in 2007, it began suffering from white nose disease, which became highly publicized.

The other cave bats are the tri-colored; the eastern small-footed; the Indiana, which is on the federal list of endangered species; and the northern long-ear, which is proposed for the federal list.

The New York bat species that winter in the South are the hoary, the eastern red, and the silver-haired.

Cutting-edge research

The white nose disease has affected all six species of bats that winter over in New York, said Herzog, caused when a fungal disease infects the animal.

The disease was first observed locally. “Many residents from the Altamont area noticed a large numbers of bats in the winter landscape,” said Herzog. The bats were leaving Haile’s Cave in Thacher Park, looking unsuccessfully for insects in the cold weather.

“This is cutting edge, in the epicenter,” he said. A DEC team led by biologist Nancy Heaslip, went to Haile’s Cave and took pictures of the bats, which were circulated to experts worldwide.

“It was obvious the white fuzz was clearly abnormal,” he said.

“They didn’t recognize it as a disease in Europe; there is no obvious mortality,” said Herzog.  He surmised this is because the bats in Europe and the disease have evolved together for thousands of years.

“It’s a story with all kinds of fascinating twists and turns,” he said. It is thought that the fungus, from someplace in Europe or Asia, was brought to North America in the Albany-Schoharie area.

A series of three criteria must be met to determine a microbial organism, said Herzog. First, the suspected cause has to occur in every case.

Second, no other known disease will explain the symptoms. And, third, the microbe must be grown in a pure culture. An animal in the lab, when exposed to it, gets the disease. “That puts the nail in the coffin,” said Herzog.

No cure has yet been found, he said. The disease is deadly because it interrupts the bat’s hibernation.

In the winter, a bat’s body temperature will typically drop from about 100 degrees to 40 degrees, which stretches their fat reserves. “When they wake up,” said Herzog, “they need more food energy…They fly out of caves in the middle of winter in a desperate attempt to find something to eat. There are no insects. They die.”

Although the Indiana bat has been endangered since before the federal list was started in the 1970s, Herzog said, all of the cave bats have been affected by the disease. It’s conceivable the disease could cause extinction, he said.

Herzog concluded, “One thing we can do to help is not disturb bats in the winter.”

Lifestyle

Although the average lifespan of a bat is probably 15 to 20 years, Herzog said, he knows, for an example, a particular bat that lived at least 34 years. That bat was marked in the 1960s with a wing band by a researcher in an abandoned Adirondack mine and was recovered 34 years later by Herzog’s predecessor.

“Bats have a unique strategy for survival,” he said of their night flights for eating insects. “It’s a high-energy lifestyle, but bats don’t reproduce rapidly like a lot of small mammals.”

Mice, for example, will have several large litters in a year but bats will have just one pup a year unless they have twins, he said; big brown bats often have twins.

Bats don’t mate for life but are “promiscuous breeders,” he said, indiscriminately mating.  With the cave bats, the females live together in colonies where they give birth and raise their young.

“Right now till mid-July, the young start to fly, the colony breaks up as the pup can fly and feed itself,” said Herzog. Female pups will eventually breed and join the maternity colony.

“Males do their own thing all summer long,” said Herzog. “If they could watch television and drink beer, they would.”

Cave bats fly in a swarm outside the entrance to their cave. “The males and females get together to mate and visit other hibernating sites,” said Herzog, which spreads genes but also spreads disease like the white-nose disease.

Less is known about the lifestyles of the bats that fly south in the winter known as tree bats. They roost in trees and are essentially solitary rather than living in colonies. Males and females live separately year-round, getting together in the late summer and fall to mate.

No one knows whether they fly south in groups like geese or Monarch butterflies, said Herzog, explaining, “It happens at night.”

He added, “The time they start to head south is an important social time. They do interact along the way.”

Rabies

Some bat species, said Herzog, are more likely than others to carry rabies — a viral infection that affects the nervous system of mammals and is fatal.

The New York species that most frequently tests positive for rabies is the big brown bat, in large part because they often live in people’s houses.

Since they live in colonies, he said, “There’s definitely a tendency to pass it to each other…Virtually all are exposed to the disease from another bat.”

Since other mammals in the wild — like raccoons, skunks, or foxes— generally succumb to rabies much more quickly than bats, there is less potential they would infect others.

“Rabies is deadly to mammals,” said Herzog, “but bats can live with the disease for a long time without showing symptoms; it never goes away.”

Although there are cases where people with rabies haven’t reported being bitten, Herzog said, “Clearly a transfer has taken place.”

Health officials, he said, can tell the different strains of rabies, for example, from bats, skunks, or raccoons. “In cases where people got the disease, but didn’t report being bitten, but had bats living in their house, it was presumed they were exposed without knowing it,” he said. “It has to get inside your skin somehow.”

Herzog said that his counterpart in Massachusetts described a case to him where a man died of rabies. “He had bats in his house for a long time and was casual about it,” Herzog said. “He got symptoms and went to the hospital too late to save him…They pieced together that he woke up in the night with a bat on him, and swatted the bat away. Instead of catching it…he went back to sleep.”

“The treatment,” he said, referring to a series of shots (described in a related story), “is relatively easy and very effective…Any skin-to-skin contact is considered exposure.”

Herzog and his colleagues have been immunized. “We treat them carefully and with respect,” he said of handling bats, noting that bats, as a species, have had rabies for “a very long time.”

While its important to catch a bat and call the county health department after exposure, Herzog warned against over-reaction when there is not exposure.

“A woman called here yesterday,” he said. “She saw a bat on the outside of her house and was afraid it would attack her. That’s not a realistic fear.”

He went on, “People are scared of anything unfamiliar…They’re not the cutest animals out there,” he conceded. “They have beady black eyes, pointy snouts, sharp teeth.”

But, he went on, “They work their way into your heart if you work with them all the time. The lack of information is a lot of it,” he said of fear of bats. “People hear they have rabies and not much more.”

A lot of wild animals impact humans more frequently in serious ways, Herzog said. Asked for an example, he cited deer causing car accidents, which kill more people than rabies. “But that doesn’t make people afraid of deer,” he said.

“People don’t think of the role of bats in a fully functional world we all want and need,” he said. “There’s a lack of understanding behind the fear.”