What Do They Look Like?

Big Brown BatNative to North, Central and Northern South America, as well as the Caribbean, the Big Brown Bat is quite the fascinating, surprisingly large, animal. It is most common in Northern Virginia and Southern Canada.

The Big Brown Bat (also known scientifically as Eptesicus Fuscus) is a medium-sized animal, with a 4 to 5” inch body length and a wingspan that ranges from 11 to 13 inches. That's over a foot long across. Big Brown Bats can weigh anywhere from a 1/2” to 5/8” of an ounce (or 14 to 16 grams). The tail is obviously a bit smaller, being only half the length of the body's size. Their fur is a moderate, medium length and is a shiny brown color. As for their ears, feet and face, they contain a darker brown, almost blackish color.

Their heads are quite big, as well, and are bigger than the males. As for their teeth, they're actually heavy, with 32 teeth capable of causing bites that are severe. They're very sharp.

The pelage (or hairy covering of a mammal) color, however, can depend on the location and the subspecies of the Big Brown Bat. The color can range anywhere from a light tan to pinkish to an olive color. And their skin texture has been known to feel almost oily.


With a lifespan of up to 19 years, the male Big Brown Bats tend to live longer than the females. And unfortunately, most will die during their first winter. This is because there wasn't enough fat stored to make it through that hibernation period. And when this happens, they'll die during their winter roost.

The Big Brown Bat is a nocturnal animal, roosting during the day. They can be found roosting in hollow trees, under loose tree bark, rock crevices and any indoor man-made structures like barns, attics and old buildings; even window shutters.


Like many other species of bats, Big Brown Bats primarily feed on insects and is particularly favoring on beetles. They also feed on moths, flying ants, wasps and dragonflies. Studies have shown, however that there are a few young bats that might possess some softer foods in their diet, compared to the adults.

Big Brown Bats will capture their prey in flight, feeding in the middle of hunting. This is what causes the sudden, frequent changes in direction you notice while watching a group of bats.

Hibernation and Feeding Habits

What actually causes mammals to hibernate is still not well-known or understood. With bats, it's apparent that the decrease in ambient temperature may be the primary cause. Their hibernation roosts can be in many different structures, either man-made environments or those that are natural. You'll notice that they prefer temperatures that are a bit cooler, tolerating conditions that other bats can't. They can also become mobile and active during hibernation in the winter.

Big Brown Bats requires their feeding activity to be confined to the warmer months, where prey insects are most active. As a result, it has to accumulate the necessary amount of fat reserves before it enters its hibernation cycle. It's estimated that Big Brown Bats can catch up to 1 and a half grams of insects for every hour they forge.

Feeding doesn't occur in heavy rain or temperature that drops below 10 degrees centigrade. If the weather is decently warm, the forge begins shortly before sunset. Once they eat, they're roosting, making use of what's called a night roost. This will cause bats to hang under someone's porch or barn for the duration of their digestion process.

During the winter months is when Big Brown Bats hibernate. Their winter locations differ from that of their summer roosts. Natural subterranean locations (caves, underground minutes) provide a stable temperature for winter roosts. When the weather finally gets warmer is when they awaken and begin to seek water and maybe even breed.

Behavior and Communication

As far as behavior goes, females will form maternity colonies. This is to rear their young. A colony's size can range anywhere from 5 members to over 700. The males tend to roost in smaller groups or completely alone. And during the later summer months, both males and females will return to roost together.

Mothers can identify their young, able to recognize them among other Big Brown Bats' babies. They recognize them either by falling from their roost or appearing lost. This will result in her young squeaking continuously. And from up to 30 feet away, the mother will be able to hear this sound. This communication is essential to the survival of the baby and can be a big help in the mother locating both of them to safer place.


Big Brown Bats will choose roosts that are secluded, which enables protection from many of their predators. Young are often taken from maternity roosts by predators such as cats, raccoons and snakes. They're taken if they fall from their roost. And flying bats can easily be capture while leaving their roosts by predators like owls and falcons or other predatory birds.

Most people don't like bats, or any bats, for that matter!

It's not surprising that people don't find it pleasant to share their homes with bats. If you see bats around your home or property around dusk, call Alliance Pest Services Bat Removal Team, Bats Away, for a free home survey to determine if you have a bat colony living in or near your home.