Tri-colored bat

The tri-colored bats perform a great agricultural service by eating grain moths as they emerge from corn cribs. (Ann Froschauer / U.S. Fish and Wildlife Service)

With Halloween quickly approaching, images of bats are appearing everywhere. October also happens to be Bat Appreciation Month.

Bats are exquisite animals. No other animal compares to Earth’s only flying mammal. Like all mammals, bats have hair and their young are born live and feed on milk. But unlike other mammals, the fingers on a bat’s hand are elongated and connected by skin to form a wing.

There are more than 1,300 species of bats that range in size from the bumblebee bat, which weighs less than a penny, to the golden-crowned flying fox, which weighs 2.6 pounds and has a wingspan of up to 5.5 feet. Except for Antarctica, bats are found on every continent, living in caves, temperate forests, deserts and tropical rainforests.

Bats eat vast amounts of insects, including some of the most damaging agricultural pests. Others pollinate plants, ensuring the production of fruits that support local economies. Fruit-eating bats in the tropics disperse seeds that are critical to restoring rainforests. Even bat droppings (called guano) are valuable as a natural fertilizer.

As primary predators of night-flying insects, bats help to control many of our most annoying pests. One insect-eating bat eats as many as 3,000 insects a night during the summer. Some bats consume crop pests, including cucumber beetles, June beetles, leafhoppers, cutworm moths and corn earworm moths. Without these natural bug zappers, farmers would lose billions of dollars in lost crop revenue as well as need to increase their use of costly pesticides.

To hunt at night, bats developed echolocation, which helps detect objects. They produce sounds at high frequencies, and by listening to the echoes of these sounds, bats are able to discern objects. Using the reflected sounds, they form pictures in their brains just like we do when we interpret reflected light with our eyes.

Bats in temperate regions either hibernate or migrate during the winter. More than half of the 47 bat species in the United States hibernate in caves in winter and move to trees and buildings in summer. Some bats live in caves all year but have different summer and winter roosts. 

During hibernation, a bat’s metabolism slows so that it uses very little of its stored fat. Heart rates slow drastically and body temperatures drop to 40–60 degrees Fahrenheit. To control body temperature, bats often roost together in great numbers.

Disturbance is a major threat to many bat species. Disturbing a maternity colony can cause mothers to drop their young or move them to a less suitable site. Waking bats during hibernation causes them to burn the precious fat reserves they have stored to survive the winter.

Preventing people from entering maternity caves and winter hibernation caves is critical. Because bats use these caves seasonally, entry may only have to be restricted during certain months. A cave entrance can be gated or fenced, preventing people from entering while allowing bats to fly in and out.

Bats are also threatened by loss of feeding or roosting habitat, usually wooded areas near water sources. As traditional roosts in trees and caves have been destroyed, many bats are seeking shelter in man-made structures. Scientists have studied the roosting requirements of bats in order to provide artificial homes. Some bats use these bat houses quite successfully.

In the last decade a new threat, white-nose syndrome, has emerged. Named for the white fungus that sometimes appears on the muzzle and other body parts of hibernating bats, white-nose syndrome has killed millions of bats in North America. First documented in New York in the winter of 2006–07, the syndrome has spread rapidly. The presence of white-nose syndrome has been confirmed in 31 states and five Canadian provinces.

Researchers associate white-nose syndrome with the fungus, Pseudogymnoascus destructans, which thrives in cold and humid conditions characteristic of caves and mines used by bats. Bats with white-nose syndrome exhibit uncharacteristic behavior during cold winter months, including flying outside during the day and clustering near the entrances of hibernacula (caves and mines where bats hibernate during the winter).

As of July 2019, 12 cave-hibernating bats, have been confirmed with the disease: big brown bat, cave myotis, the endangered Indiana bat, eastern small-footed bat, little

 brown bat, endangered gray bat, long-legged bat, the threatened northern long-eared bat, western long-eared myotis, Yuma bat, southeastern bat and tri-colored bat.

The fungus has also been detected but with no confirmation of the disease, in the western small-footed bat, eastern red bat, silver-haired bat, Rafinesque’s big-eared bat, Townsend’s big-eared bat, the endangered Virginia big-eared bat, the endangered Ozark big-eared bat and Mexican free-tailed bat.

All of these species range within all or part of the Chesapeake watershed except for cave bats, gray bats, long-legged bats, Mexican free-tailed bats, Rafinesque’s big-eared bats, western long-eared myotis, western small-footed bats and Yuma bats.

A network of state and federal agencies, universities and organizations is working to investigate the source, spread and cause of white-nose syndrome to develop strategies to minimize its impact on bats. Scientists have developed ways to detect P. destructans on bats and in the environment, using UV light and molecular analyses.

Research is looking at biological treatments, altering hibernation conditions to slow fungal growth or improve bat survival, and vaccines to boost bats’ resistance to the disease. Researchers are also looking into molecular and genetic tools to reduce the ability of the fungus to cause disease.

What can you do?

  • Minimize disturbance to natural bat habitats by reducing outdoor lighting, curtailing tree clearing and protecting streams and wetlands.
  • Build a bat house in your yard.
  • Report unusual bat behavior to your state natural resource agency. Unusual behavior includes bats flying during the day when they should be hibernating (December through March) and bats roosting in sunlight on the outside of structures. Bats flying in the middle of the day are unusual. Bats unable to fly or struggling to get off the ground should be reported.
  • Do not go into caves and mines where bats are known or suspected to hibernate.
  • Honor cave closures and gated caves.
  • Researchers and cavers should follow decontamination guidelines to reduce the possibility of spreading the disease.

For news on white-nose syndrome research, visit To learn how to protect bats, call Bat Conservation International, 800-538-2287.


Kathryn Reshetiloff, a Bay Journal columnist, is with the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office in Annapolis.

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