© Serah Rose Roth
© Serah Rose Roth

Bats are truly remarkable animals as well as our only flying mammals. Unfortunately their unwarranted reputation has prevented many people from appreciating how beneficial and unique they are.

Bats belong to the order Chiroptera, which means "hand-wing." Their wings are composed of two thin layers of skin or membrane, attached to elongated finger bones. Each membrane has four fingers and a thumb, which control the wing's movement. The thumb, located at the top of the wing, acts as a hook with which the bat is able to crawl on flat surfaces. 

Bats in Massachusetts

There are nine species of bats that have historically lived in Massachusetts, several of which are state listed as Endangered. Here are profiles of a few select species.

Eastern Red Bat (Lasiurus borealis)

Eastern red bat © NPS
Eastern red bat © NPS

Usually solitary, it roosts in trees, hanging from one foot and swaying slightly to resemble a dead leaf. The female gives birth to an average of three young in early summer. In autumn the eastern red bat migrates along the east coast using the same routes as many birds. Little is known about its migratory destinations. Common

Hoary Bat (Lasiurus cinereus)

Hoary bat © William Leonard, NPS
Hoary bat © William Leonard, NPS

Our largest bat, this seldom-seen creature has striking fur with a frosted appearance. During the day it roosts alone in the dense foliage of a tree, preferably a conifer. It generally avoids human structures. The hoary bat has the most extensive range of any North American bat: it’s found from Canada to Chile and Argentina. It is also partially migratory. Northern populations move to southern states where it is warm enough to roost in the open. Common

Little Brown Bat (Myotis lucifugus)

Little brown bat © NPS
Little brown bat © NPS

This species was once the most common bat in Massachusetts, but the white-nose syndrome epidemic in its wintering caves has dramatically reduced its population. Females form large nursery colonies in the late spring and summer and may roost in buildings. For the first few days of its life, the young bat clings to its mother while she hunts for food at night. Endangered in Massachusetts

Big Brown Bat (Eptesicus fuscus)

Big brown bat © USFWS
Big brown bat © USFWS

In summer, this glossy brown bat lives in buildings and trees. In the winter it may hibernate in a cave, but it typically inhabits a dry area such as an attic where the white-nose fungus cannot survive. This abundant species hunts for insects in a wide variety of habitats. Common

Tricolored Bat (Perimyotis subflavus)

Tricolored bat © USFWS
Tricolored bat © USFWS

Formerly called the eastern pipistrelle, this animal is named for its fur color: each hair is dark at the base, light in the center, and dark at the tip. It is one of the first bats to emerge and begin flying at night. This bat hibernates in caves and mines, where the white-nose syndrome epidemic has resulted in its status as being endangered in the state. Endangered in Massachusetts

Benefits of Bats

All bats found in Massachusetts are insectivores. They feed primarily at night, catching thousands of mosquitoes, moths, and other night-flying insects.

It is estimated that an individual bat can eat 600 insects per hour. Dr. Thomas Kunz, a bat researcher at Boston University, estimates that the bats living within Route 128 eat 13 tons of insects each summer.

Life Cycle

Bat on a tree © David McChesney
© David McChesney

During the late spring and summer pregnant, female Little Brown and Big Brown bats form large nursery colonies and roost in dark, hot places such as, attics, barns, and other outbuildings to give birth and raise their young.

Males, often solitary or in groups less than a dozen in the summer, roost in cooler spots behind window shutters, and awnings and under the bark of trees. Bats rest in these protected roost sites during the day leaving at sunset to search for food.

Mating takes place in the fall before hibernation and the sperm is then stored in the female's uterus throughout the winter. The eggs become fertilized when hibernation ends in the spring and in June or early July the females gather into "nursery colonies" and give birth. The gestation period for both the Little Brown and the Big Brown bats is 50 to 60 days.

Little Brown Bats give birth to one offspring and the big brown delivers one or two. As soon as the baby is born it clings to its mother, attaching itself to a nipple and, for the first few days, is carried by her when she flies at night searching for food. At three or four weeks the young begin to take short flights and catch their own food. When the young are able to feed themselves the "nursery colony" disbands to begin preparing for hibernation.


The nursery colonies break-up in late summer and little brown bats migrate to hibernation caves and mines, mainly in western Massachusetts, upstate New York and Vermont. Big Brown Bats, which are more tolerant of cold temperatures, may migrate to caves or spend the winter in the same buildings they occupy the rest of the year.

Bats choose hibernacula with temperatures between 30 degrees and 40 degrees above zero. If the temperatures drop below freezing they will move to a location with more favorable temperatures. As hibernation begins, breathing slows to one breath every five minutes and the body temperature drops until it is only slightly higher than the air surrounding it.


Bats are not blind as many people believe. On the contrary, they have excellent eyesight but use echolocation in the dark to detect objects as minute as a human hair. When in flight they continuously emit high frequency sounds (unheard by humans) which bounce back to their ears enabling them to locate objects, as well as the flying insects they feed on.

The bat uses the increasing frequency of the echoes to zero-in on its target. During its search for food the bat may emit 10-20 pulses per second, increasing to 500 per second just before it attacks its prey.

Situations & Solutions

Bat found resting in aa kiosk at Felix Neck Wildlife Sanctuary © Justen Walker
© Justen Walker

Because bats are so efficient at controlling many of bothersome insects, it is advantageous to leave them alone. That being said, there are instances where a bat is not welcome, such as inside your home.

Bat in a Living Space

Unintentionally, bats may enter areas occupied by people through an open window or door, or an opening from a colonized attic or wall. A bat indoors is not necessarily a sick bat—it may be a young bat who tried to follow its mother outside and took a wrong turn or it may have followed a moth through an open window.

An attempt can be made to capture the bat if it lands in a spot where a coffee can or wide-mouthed jar can be safely placed over it. Slide cardboard under the coffee can, leave the bat under the container and notify the local animal control officer or police. It will be transported to the Department of Public Health Laboratory for testing.

Bat in Child's Room

In all situations where a bat is found in a child's room—or even an adult's room—contact the Massachusetts Department of Public Health at 617-983-6800 (available 24-hours a day).

Because a bat's teeth and claws are so small, it's impossible to determine whether someone has been bitten. Therefore, it's up to the MDPH to determine whether you or your child should receive post-exposure prophylaxis (PEP) shots.

Bat in Other Areas of the Home

Confine the bat to one room by closing doors. Open windows, turn off the lights, and leave the room. Hitting the bat or throwing things at it will cause it to become disoriented making it harder for the bat to find its way out.

Do not try to capture the bat unless there is the possibility it has bitten or scratched someone. Make an attempt only if the bat lands and there is no risk in placing a wide-mouthed jar or coffee can over it. Contact the local animal control officer or police department.

Bat Proofing Your Home

We encourage hospitality towards bats, however if there is a substantial reason to exclude them this should be undertaken only during the month of May, and from mid-August to mid-October. In between those periods young bats could be blocked inside and the decaying bodies will cause a severe odor problem. How to keep bats away >

Finding an Injured Bat

Every now and then during the winter a live bat will be found on the ground outdoors or possibly flying around indoors. No one can assume the reason it emerged from hibernation so it is best to leave it alone and contact a professional.

If the bat is indoors, contact the Massachusetts Department of Public Health at 617-983-6800.

White-Nose Syndrome

First recorded in the winter of 2006-2007, white-nose syndrome (WNS) is a disease that’s affecting bats in enormous numbers. More than a million of these mammals have died in the Northeast and Canada, and some hibernacula (sites, like caves, where bats hibernate) have witnessed a 90- to 100-percent decimation in their population.

Bats with the disease are often marked with a white fungus that covers the nose and other parts of the body. They also exhibit abnormal behavior, such as flying during the day or in the winter when they should be hibernating.  

Scientists still don’t know what causes this disease, but signs point to a cold-loving fungus called Geomyces destructans that gets in the bats’ skin. The Department of the Interior’s U.S. Fish and Wildlife Service has coordinated a national management plan to address WNS, its potential causes, and ways to stop its spread.

What You Can Do 

In order to minimize the spread of WNS, stay out of known hibernacula such as caves and mines—especially during the winter.

Because bats depend on insects for food, providing a chemical-free, natural habitat around your property will allow these insect predators to do their job.

Stay Informed

For the latest news about white-nose syndrome, visit Bat Conservation International. If you see dead or dying bats with a white powdery area around their nose, notify the Massachusetts Department of Fisheries and Wildlife

By the Numbers: Bats

By the Numbers: Bats

Don't let tales of the vampire, blood-sucking variety of bat found in folklore scare you off from learning about this most benevolent creature. Get the facts >