In summer as children, we were allowed to stay out until dusk. In our northern part of the Central Time Zone, even on its eastern edge, dusk came late. I remember most the mosquitoes, fireflies, and bats. Some nights I would watch the bats as darkness fell. First there would be only one, then two, and by the time it became truly dark, there would be half a dozen or more swooping above us at what seemed a discreet distance. But who knew if they were even aware of us?
I would try to follow one with my eyes to judge its circuit. That was nearly impossible though because they were so quick, and their flight would take them through trees where I would lose sight of my mark for a second; then I couldn’t tell if it was my bat or another one I was watching. I imagined that the bats operated in little groups that patrolled a defined area with maybe six bats per cell. I imagined these cells occurring contiguously all over the county and then all over the state and ultimately all over the country; I figured there would be hundreds and thousands and millions of bats. Thinking about that, I got the same feeling as when I stared at the stars and tried to infer infinity.
In those days, bats were regarded as vermin that lived in attics, carried rabies, and were slightly creepy and, at best, of little or no use. Now as then, there are fears and misconceptions about bats.
Some of these are silly. That bats are attracted to human hair is one of those; or that they’ll get stuck in hair while hunting insects. Try throwing a stick into the air where bats are hunting overhead; they’ll immediately scatter, just as minnow do when a pebble is dropped into a pond. All the swooping and acrobatics that bats exhibit involve locating and catching insects in the dark on the wing; bats certainly can distinguish humans—and their sticks—from prey.
Some are accepted as figures of speech: “blind as a bat”. But bats are not blind. Some fruit bats have excellent night vision, which they use to find the flowers and fruits they pollinate and eat. In the dark, though, bats also “see” by echolocation. Bats emit a series of short, high-pitched sounds that bounce off objects and surfaces, creating an echo that the bat perceives. It’s an acutely sensitive system that allows bats to discriminate the size, shape, direction, distance, and motion of an object (insect, human, or otherwise) and that may have applications for blind people.
Some are a mixture of fancy and fact. Bats don’t attack people, but they can carry disease. They are highly mobile creatures that range far and wide in small groups and roost in large communal colonies, which make them good hosts for pathogens and excellent potential transmitters of disease. However, the threat to humans in North America is minimal.
Rabies is the predominant disease concern. Rabies has been recognized for at least 4000 years and is typically transmitted in saliva from the bite of an infected animal. It’s a viral disease of warm-blooded animals (including humans) that affects the central nervous system. It’s most often seen in dogs, cats, raccoons, skunks, foxes, bats, and coyotes. The World Health Organization estimates that 55,000 people die from rabies each year, mostly from contact with rabid dogs, but in North America, pet and livestock vaccination programs have all but eliminated human rabies. An average of two people per year died from rabies transmitted by bats in North America between 1995 through 2009.
Among other things we know about bats is that they may look like winged rats, but they’re not rodents. They are far more closely related to humans than they are to rodents. Worldwide, there are as many as 1100 species of bats. Most (70%) eat insects; most of the rest eat fruit. There are three species of “vampire” (carnivorous) bats that live in Central and South America (their teeth are not like hypodermic needles, though; they lap rather than suck blood).
Bats come in a variety of sizes. The smallest is the Kitti’s Hog-Nosed bat (Craseonycteris thonglongyai), also known as the bumblebee bat. It’s endangered, insectivorous, and lives in Southeast Asia. It’s about 1.25 inches long and is the world’s smallest mammal. The largest bat is the rare and endangered Giant Golden-Crowned Flying-Fox (Acerodon jubatus), a fruit bat that weighs nearly 3 pounds and has a wing span of almost 5 feet. It lives in the Philippines.
Bats are the single true flying mammal, and some are prodigious flyers. The hoary bat (Lasiurus cinereus) commonly occurs throughout North and South America. Like some other bats, it is migratory and will migrate from Canada to the southern USA; it is known also to have flown from North America to Hawaii (about 3000 miles). It is Hawaii’s only indigenous land mammal and is endangered there. It is predatory and prefers moths.
Migratory bats are the exception in the temperate North America. Most of our bats hibernate in caves (or mines) during winter; they roost in trees or buildings during summer.
Bats are not vermin. They play a significant ecological role. In desert and tropical climates, bats are important pollinators. Many tropical plants (mangoes, bananas, and guavas) are dependent on bats for pollination; some are entirely dependent on bats for pollination and seed distribution. In tropical rainforests, almost all seeds scattered in cleared areas are dropped by bats. In North America, bats are the primary predator of night-flying insects. A single bat can eat as many as 1000 mosquitoes in an hour. Bats also feed on beetles, leafhoppers, and moths, many of which feed on—and destroy—important food crops.
An abundance of bats seems to be an indicator of a well functioning ecosystem, and there is evidence that where bat populations have been disrupted, insect pest populations have risen. Worldwide, bats are endangered. Of the 45 species that inhabit the USA, six are endangered.
In North America, one of the main threats to bats is habitat loss resulting from urbanization, surface mining, municipal lake and reservoir construction (which flood roosting caves), and casual cave exploration (spelunking). Pesticides and wind farms positioned in their migratory pathways also strain bat populations. Another threat that seems to have the potential of decimating bat populations is White-Nose Syndrome. Apparently diseased bats with white muzzles were observed in a cave near Albany, NY, in 2006; dead bats were observed also. This syndrome seems to affect hibernating bats, and since it was first identified, sick, dying, and dead bats have been found in and around caves from New Hampshire to Tennessee. As many as 1 million bats have died. Federal and state laboratories are actively studying the syndrome. A newly discovered fungus (Geomyces destructans) that grows under cold conditions and infects bat skin may be associated, but the cause of the bat deaths is unknown. For more information see http://www.fws.gov/WhiteNoseSyndrome/index.html; verified 1 Aug. 2010.
Bat houses are a way of compensating for bat habitat loss. There are 10 North American species that nest in bat houses. So if you’re interested in supporting bat populations, there are lots of resources for bat houses on the internet, from commercially constructed ones to simple plans and information. A bat colony in your backyard will have the added benefits of reducing the number of insects in your yard and discouraging bats from roosting in your attic, where they don’t really want to live anyway.