As dusk settles over Boston’s historic neighborhoods and green spaces, a remarkable transformation takes place in the skies above. While most residents wind down their day, seven distinct species of bats emerge to begin their nightly hunt for insects.
These flying mammals represent some of the most misunderstood yet beneficial wildlife sharing your urban environment.
Boston’s bat population plays a crucial role in controlling insect numbers, with an individual bat able to eat up to 125% of its body weight in insects in a single night MSPCA-Angell.
From the common Big Brown Bat roosting in attics throughout Brookline and Cambridge to the rare Tricolored Bat struggling against White-nose Syndrome, each species has adapted uniquely to life in and around Massachusetts’ largest city.
Understanding which bats call Boston home helps you appreciate these nocturnal neighbors and recognize when their presence requires attention or simply admiration from afar.
1. Little Brown Bat
The little brown bat, scientifically known as Myotis lucifugus Mass Audubon, once held the distinction of being the most abundant bat species in Massachusetts Mass.gov. However, this small mammal has faced devastating population declines that have fundamentally altered its status throughout the region.
Physical Characteristics
The Little Brown Bat’s body measures 3.1 to 3.7 inches long, including the tail, and has an 8.5 to 10.5-inch wingspan Mass Audubon. These dimensions make them noticeably smaller than their Big Brown cousins. Adult Little Browns have a wingspan of 6-9 inches Batguys, creating a distinctive silhouette when observed in flight.
The fur coloring ranges from brown to reddish-brown, with lighter coloration on the belly. Their small, delicate features include pointed ears and a relatively short snout. When you compare droppings between species, little brown guano is smaller than a grain of rice Batguys, providing one identification method when the bats themselves aren’t visible.
Habitat and Distribution
Little Brown Bats migrate to the Boston area every spring from the mid-Atlantic states, starting to show up in May and usually here in full-force by the second week of June Batguys. This migratory pattern distinguishes them from the year-round resident Big Brown Bats.
Little brown bats are found in very large colonies throughout Eastern Massachusetts Batguys, though their numbers have declined dramatically since the arrival of White-nose Syndrome. These bats seem to show up in clusters every spring, with some years bringing dozens of calls for little browns along the coastline while inland areas remain quiet, and other years seeing the reverse pattern Batguys.
Behavior and Diet
Little brown bats are highly effective insect predators, targeting mosquitoes, midges, and other small flying insects. They use echolocation to navigate and hunt in complete darkness, emitting high-frequency sounds that bounce off objects and return information about their surroundings.
During summer months, females form maternity colonies in warm, dark spaces like attics where they give birth to single pups. The gestation period lasts 50 to 60 days, with births typically occurring in June or early July. Young bats remain dependent on their mothers for several weeks before learning to fly and hunt independently.
Conservation Status
The Little Brown Bat population declined by more than 99% after the onset of White-nose Syndrome Mass.gov, leading to its listing as Endangered in Massachusetts Mass Audubon. This fungal disease attacks bats during hibernation in caves and mines, causing them to wake frequently and deplete their fat reserves before spring arrives.
The devastating impact of White-nose Syndrome represents one of the most catastrophic wildlife diseases in North American history. Conservation efforts focus on protecting remaining populations and researching potential treatments, though no cure currently exists.
2. Big Brown Bat
The big brown bat, designated scientifically as Eptesicus fuscus Mass Audubon, stands as the most common species of bats in Massachusetts Batguys. These robust bats have successfully adapted to urban environments and currently represent the bat species you’re most likely to encounter in Boston.
Size and Appearance
The Big Brown Bat has a glossy exterior and ranges from 4.3 to 5.1 inches in length with a 12 to 13-inch wingspan Mass Audubon. This larger size makes them easier to observe in flight compared to their smaller relatives. The wingspan of adult Big Brown bats in Massachusetts is between 11-13 inches Batguys.
Their coloring varies from light brown to dark brown, with a notably shiny coat that helps distinguish them from other species. The face, ears, and wing membranes appear dark, almost black, creating a striking contrast with the lighter fur. Guano from Big Browns always smells like it is wet and moist Batguys, and individual droppings are larger than a grain of rice.
Year-Round Boston Residents
Big Browns are year-round residents in the Bay State Batguys, setting them apart from the migratory Little Brown Bats. We see healthy populations of these bats in downtown Boston, with the towns of Brookline, Somerville, Newton and even downtown Cambridge all having healthy populations of big brown bats Batguys.
These bats are active from late winter through the late fall, and once the cold weather arrives and nighttime temperatures dip down into the 30’s, Big Browns go into hibernation Batguys. Unlike cave-hibernating species, Big Brown Bats typically inhabit a dry area such as an attic where the white-nose fungus cannot survive Mass Audubon.
Roosting Habits
We typically find colonies of Big Brown Bats in attics that range anywhere from 2-200 bats Batguys. With very little natural habitat left in Eastern Massachusetts, these bats now hibernate in attics and rooflines of homes, burrowing under insulation or dropping down wall-voids in an effort to stay warm Batguys.
Big Brown bats have a high tolerance for cold weather, and every year we see Big Brown Bats flying at night and even roosting on the exterior of houses in January and February Batguys. This hardiness contributes to their success in urban environments.
Impact on Homeowners
Big Brown Bats definitely cause the most problems for homeowners in Massachusetts Batguys. These bats are not afraid to enter attics and go exploring once they’re inside, venturing deep into cathedral ceilings and other areas inside the structure Batguys. Ninety-nine percent of the bats that we remove from the living space of homes are Big Brown Bats Batguys.
Despite the challenges they can create for homeowners, Big Brown Bats provide significant ecological benefits. Their voracious appetite for beetles, including agricultural pests like the Cucumber Beetle, makes them valuable allies for farmers and gardeners throughout the region.
3. Eastern Red Bat
The eastern red bat, known scientifically as Lasiurus borealis Mass Audubon, brings a splash of color to Boston’s bat community. This solitary tree-dwelling species displays distinctive behaviors and appearance that set it apart from the more common colonial bats.
Distinctive Coloration
Males have distinctive rusty red-colored fur, and females have more of a soft shade of red, with both having white patches of fur on their shoulder Bird Watching HQ. This striking coloration makes Eastern Red Bats among the most visually distinctive bat species when observed up close.
The eastern red bat is a small bat with a wingspan of only nine inches Pestex. Their small size combined with their unique coloring creates an unmistakable appearance that aids in identification.
Solitary Lifestyle
Usually solitary, the Eastern Red Bat roosts in trees, hanging from one foot and swaying slightly to resemble a dead leaf Mass Audubon. This remarkable camouflage strategy protects them from predators during daylight hours. Unlike colonial bats that gather in large groups, Eastern Red Bats prefer to spend their days alone in tree foliage.
Eastern Red Bats can be found in forests Mass Audubon and wooded areas throughout Boston’s parks and green spaces. They favor deciduous trees where their coloring blends with autumn leaves and tree bark.
Reproductive Success
Unlike most bats that only produce one offspring, Eastern Red Bats have three pups in a litter Bird Watching HQ. The female gives birth to an average of three young in early summer Mass Audubon. This higher reproductive rate helps maintain their populations despite various environmental challenges.
The ability to produce multiple offspring per year represents an adaptation that partially compensates for the higher mortality rates associated with their exposed roosting sites and solitary lifestyle.
Migration Patterns
In autumn the Eastern Red Bat migrates along the east coast using the same routes as many birds Mass Audubon. This migration takes them to warmer climates where insects remain active during winter months. Little is known about its migratory destinations Mass Audubon, though research suggests they travel to the southern United States.
Eastern Red Bats are relatively fast flyers with good maneuverability Bird Watching HQ, adaptations that serve them well during their long migratory journeys. Their diet consists primarily of moths, though they consume various flying insects depending on availability.
4. Hoary Bat
The hoary bat, scientifically designated as Lasiurus cinereus Mass Audubon, claims the title of the largest bat species found in Massachusetts Animal Spot. This impressive mammal remains relatively uncommon in urban Boston due to its preference for less developed areas.
Impressive Size and Appearance
The hoary bat has a wingspan of up to 16 inches Pestex, making it substantially larger than any other bat species in the region. They are yellow/brown or dark brown in color Pestex, but their most distinctive feature is their frosted appearance.
The Hoary Bat has striking fur with a frosted appearance Mass Audubon. This unique coloring comes from white-tipped hairs scattered throughout their coat, creating the “hoary” or frosty look that gives them their common name.
Habitat Preferences
During the day it roosts alone in the dense foliage of a tree, preferably a conifer Mass Audubon. It generally avoids human structures Mass Audubon, making encounters with this species less common in densely populated areas of Boston.
You’ll typically find Hoary Bats in Massachusetts roosting on trees in woodland forests as solitary bats that roost in open foliage Bird Watching HQ. The remaining forested areas within Boston’s parks and along the outskirts of the metropolitan area provide the habitat these large bats require.
Hunting Behavior and Diet
This species prefers to hunt for prey while flying over wide-open areas or lakes, hunting alone and enjoying eating moths Bird Watching HQ. They’re known to travel up to 24 miles in a single night to gather food Bird Watching HQ, demonstrating remarkable endurance and range.
The hoary bat’s hunting strategy differs from smaller species. Rather than pursuing tiny insects in cluttered environments, they target larger prey in open spaces where their size and power provide advantages over smaller competitors.
Extensive Range
The Hoary Bat also has the most extensive range of any North American bat: it’s found from Canada to Chile and Argentina Mass Audubon. Northern populations often move to southern states where it is warm enough to roost in the open Mass Audubon.
Hoary Bats form “flocks” when migrating south in late summer, but they don’t hang out with other bats normally Bird Watching HQ. This seasonal congregation represents one of the few times these typically solitary animals gather in groups.
Conservation Challenges
Though the Hoary Bat is not endangered, it does suffer a loss in numbers because of wind turbines Bird Watching HQ. It’s thought that they confuse the wind turbine with a tree as they seek a place to rest Bird Watching HQ during migration, leading to fatal collisions.
5. Silver-haired Bat
The silver-haired bat, bearing the scientific name Lasionycteris noctivagans Mass Audubon, adds another migratory species to Boston’s bat community. These medium-sized bats display distinctive coloring that makes them relatively easy to identify when observed closely.
Physical Description
The Silver-haired Bat has dark brown fur with silver tips on the backside Mass Audubon. They are typically about 3.9 inches in length and weigh about 10.5 grams Mass Audubon. Silver-haired bats have a wingspan of up to 10 to 12 inches Pestex.
They are black or dark brown in color, with silver-tipped hairs on their back and shoulders Pestex. This distinctive frosting effect creates a shimmering appearance that inspired their common name. The contrast between the dark base color and silver tips makes them visually striking when illuminated.
Seasonal Presence
Silver-haired Bats can only be found in Massachusetts during the summer and migrations and do not breed here Mass Audubon. This seasonal pattern means you’ll most likely encounter them during warmer months when they pass through the region during spring and fall migrations.
Silver-haired bats are found in wooded areas of Massachusetts, where they roost in trees during the day Pestex. They can be found in forests alongside bodies of water Mass Audubon, making Boston’s Charles River corridor and surrounding parks potential habitat.
Feeding Habits
These bats eat insects, such as moths and beetles Pestex. They emerge at dusk to hunt, typically flying slower and more deliberately than some smaller bat species. Their medium size allows them to target a range of insect prey, from tiny midges to larger moths and beetles.
Silver-haired bats often hunt near water sources where insects congregate. The ponds and waterways throughout Boston’s park system provide excellent foraging opportunities during their time in the area.
Tree-Roosting Behavior
Unlike Big Brown and Little Brown bats that readily inhabit buildings, silver-haired bats show a strong preference for natural roosting sites. They typically roost under loose bark on trees or in tree cavities, rarely entering human structures unless migrating individuals accidentally find their way inside.
This preference for tree roosting means that maintaining mature trees with loose bark in urban parks supports silver-haired bat populations. Dead standing trees, often called snags, provide particularly valuable habitat for these and other tree-roosting species.
6. Northern Long-eared Bat
The northern long-eared bat, scientifically known as Myotis septentrionalis Mass Audubon, stands out among Boston’s bat species for its distinctive physical features and tragic population decline. This medium-sized bat has become one of the region’s most imperiled mammals.
Identifying Features
Long-eared Bats are easily recognized by their long ears—which can even reach past its nose Mass Audubon. These remarkably elongated ears provide the most reliable identification characteristic, visible even in flight under good lighting conditions.
The northern long-eared bat is a medium-sized bat with a wingspan of up to 9 to 10 inches Pestex. They are light brown in color and can be found in wooded areas of the state Pestex. Fur and wing membranes are tan, with black ears and black wings, long tail and a wingspan up to 10 inches Bird Watching HQ.
Summer Habitat
Northern Long-eared Bats are found in Massachusetts in forested habitats with spruce and pine trees Bird Watching HQ. They typically roost in trees during the summer and switch to a new roost every other day Bird Watching HQ. This frequent roost-switching behavior may help them avoid predators and parasites.
During summer months, females form small maternity colonies in tree cavities, under bark, or occasionally in buildings. Males typically roost alone throughout the summer season.
Hibernation Behavior
In the fall, these bats migrate to caves to hibernate with other species of bats Bird Watching HQ. This cave-hibernating behavior has made them particularly vulnerable to White-nose Syndrome, which thrives in the cool, humid conditions of underground hibernacula.
Unlike Big Brown Bats that can hibernate in dry attics, northern long-eared bats require the stable temperatures and humidity found in caves and mines. This dependence on specific hibernation sites has contributed to their precipitous decline.
Population Crash
These bats were once a common species across the state but have suffered massive population drops due to White-nose Syndrome Mass Audubon. Status: Endangered in Massachusetts Mass Audubon. All four bat species that spend winters in caves or mines were listed as Endangered in Massachusetts in 2012 Mass.gov, including the northern long-eared bat.
The fungus causing White-nose Syndrome grows on bats during hibernation, irritating their skin and causing them to wake frequently. These repeated arousals deplete their stored fat reserves, leading to starvation before spring insects become available.
7. Tricolored Bat
The tricolored bat, scientifically designated as Perimyotis subflavus Mass Audubon, represents one of Boston’s smallest and most distinctively colored bat species. Formerly known as the Eastern Pipistrelle, this bat has suffered severe population losses in recent years.
Unique Coloration
The Tricolored Bat is named for its fur color: each hair is dark at the base, light in the center, and dark at the tip Mass Audubon. This three-banded coloring creates a subtle but distinctive appearance that inspired both its common and scientific names.
The Tricolored Bat is the smallest, with a wingspan of about 8-10 inches Animal Spot. They are brown or reddish-brown in color and have three stripes on their back – one dark gray stripe, one yellowish stripe, and a dark brown stripe Pestex. The overall effect creates a mottled, multicolored appearance.
Size and Build
It is a larger bat with around a 12-inch wingspan, brown fur with black ears, wings, and feet, with wings that are hairless Bird Watching HQ. Despite being among the smallest bats in the region, tricolored bats are effective insect predators.
Their small size allows them to pursue tiny insects in cluttered habitats where larger bats cannot maneuver effectively. This niche specialization reduces competition with other bat species for food resources.
Roosting and Hibernation
This bat hibernates in caves and mines, where the white-nose fungus thrives Mass Audubon. These bats can be found in wooded areas of the state as well as mines and caves Pestex. During summer, they roost in tree foliage, choosing locations that provide concealment and protection from weather.
If you look, you’ll find these bats inside caves, tunnels, or other human structures Bird Watching HQ during hibernation season. The specific microclimate requirements for hibernation limit their distribution and make them vulnerable to disturbance.
Diet and Ecological Role
This nocturnal bat primarily eats insects, especially ones that fly at night, with their preference being beetles, particularly the Cucumber Beetle Bird Watching HQ. The Cucumber Beetle is their favorite, which benefits farmers because these insects are terrible pests for agriculture Bird Watching HQ.
By targeting agricultural pests, tricolored bats provide valuable ecosystem services to farms throughout Massachusetts. Their small size allows them to consume enormous numbers of tiny insects relative to their body weight.
Severe Population Decline
Status: Endangered in Massachusetts Mass Audubon. Tricolored Bats used to be considered one of the most common bats around, but unfortunately, their numbers have been decimated by White-nose syndrome Bird Watching HQ. It’s thought that 70% of their population has succumbed to this fungal disease Bird Watching HQ.
This catastrophic decline has transformed the tricolored bat from a common species to one of serious conservation concern. The Tricolored Bat’s natural predators include many birds of prey, snakes, skunks, other bats, and Northern Leopard Frogs Bird Watching HQ, demonstrating their vulnerability to various threats.
Living Safely with Boston’s Bats
Understanding how to coexist with Boston’s bat population requires balancing appreciation for these beneficial mammals with legitimate safety concerns. During the summer months, it is not unusual to find a bat in a home in Boston, with most of these animals having accidentally flown into your home and now trapped Boston.
Health Considerations
Bats sometimes carry rabies and may spread it to people or animals through bites or scratches Boston. However, bats are not normally aggressive, and will try to avoid contact with humans and pets MSPCA-Angell. The actual risk remains low when you follow appropriate precautions.
If a person may have been bitten or scratched, it is important to capture the bat and have it tested for rabies Boston. Testing becomes essential if the bat was found in a room with a sleeping person, as bats have small sharp teeth, which may not leave a visible bite mark, and a bite from a bat during the night may not awaken a sleeping person Boston.
Capturing a Bat Safely
If you find a bat in your home, wearing heavy gloves, cover the bat with a pail, coffee can, or similar container, then slide cardboard under the container to trap the bat inside and tape the cardboard to the container Boston. Boston residents can contact Boston Animal Control at 617-635-5348 for recommendations or assistance in capturing the bat Boston.
When isolating a bat, stay close to the walls because bats fly in u-shaped patterns, flying lower in the center of the room MSPCA-Angell. This knowledge helps you avoid the bat’s flight path while directing it toward an exit.
Bat-Proofing Your Home
Examine your home for holes that might allow bats entry, use window screens, chimney caps, and draft guards beneath doors to attics, and fill electrical and plumbing holes with stainless steel, wool, or caulking Boston. Observe where the bats exit at dusk and keep them from re-entering by loosely hanging clear plastic sheeting or bird netting over these areas (bats can leave, but cannot re-enter) Boston.
Avoid permanently sealing openings from May through August, as many young bats are unable to fly and may die trapped inside or make their way into living quarters Boston. Timing exclusion work appropriately ensures you don’t trap flightless young bats inside your home.
Supporting Bat Conservation
Installing a bat house on your property can provide a safe environment for bats, while protecting your yard from pest insects, like mosquitoes, moths, and beetles Mass.gov. Properly constructed and strategically placed bat houses can be an important tool in assisting bat survival Mass.gov.
Bats seek shelter under peeling bark on dead trees, so if you have dead or dying trees on your property, leave them standing as potential roost sites for bats Mass.gov. Reducing pesticide use helps protect the plants bats depend on while supporting the broader ecosystem, as pesticides make it difficult for bats to find healthy food to eat Mass.gov.
Appreciating Their Ecological Value
The Greater Boston area is home to millions of mosquitoes during the summer months, with some of these mosquitoes carrying diseases such as eastern equine encephalitis Batguys. Both species of our native bats feed heavily on mosquitoes and are instrumental in keeping the mosquito population in check Batguys.
A single bat of either species can eat over 600 mosquitoes in a one-hour period Batguys, demonstrating their remarkable pest control capabilities. This natural service reduces both nuisance insects and disease risk throughout the metropolitan area.
The seven bat species found in Boston represent a diverse group of mammals facing both opportunities and challenges in the urban environment.
From the abundant Big Brown Bat to the critically endangered Little Brown Bat, each species contributes to the ecological health of the region while adapting to life alongside millions of human residents.
By learning to identify these bats and understanding their behaviors, you can better appreciate these remarkable flying mammals and contribute to their conservation.
Whether you encounter bats roosting in your attic or observe them hunting insects during evening walks through Boston Common, recognizing which species you’re seeing enriches your connection to the city’s wildlife and highlights the importance of protecting these vulnerable yet beneficial neighbors.
