Big Brown Bats

The scientific name of the big brown bat Eptesicus fuscus

All about the Big Brown bat

Wondering what the difference is between a Little Brown bat and a Big Brown bat? Well “Big Brown bat” is no misnomer. The only real difference between these two species is the size.

What does a Big Brown bat look like?

Not counting the tail, the Big Brown bat is about five inches long with a wingspan of up to 13 inches. Like the Little Brown Bat, the Big Brown Bat has long, glossy, dark brown to copper colored fur on its upper side and lighter gray fur underneath. The bat’s wing membranes, ears, feet, and face are dark brown to black. The Big Brown bat has fleshy lips, small rounded ears, and a broad nose. The Big Brown bat weighs between a ½ ounce and 1 ½ ounces.

Big Brown Bat Close Up

Big Brown Bat Close Up

Where does the Big Brown bat live, and what does it eat?

Ranging from the northernmost parts of Canada to northern South America and everywhere in between, the Big Brown bat species is far-reaching. It is also found in the Caribbean islands. Big Brown bats live in a wide range of habitats from mountains to deserts, meadows, cities, and chaparrals. The Big Brown bat can withstand much harsher conditions than can other species of bats, which is why its range is so widespread.

There are three main roosts for the Big Brown bat: daytime roosts, nighttime roosts, and hibernation roosts. While the bat is active, it will roost day and night in buildings, caves, under rocks or piles of wood, or in man-made structures like houses, buildings, and churches. It is not uncommon to find bats in the attic of structures that aren’t properly sealed tight. Bats can also be found inside walls, chimneys, fireplaces, attics, shutters, eaves, and bell towers. In any of its roosting sites, Big Brown bats pack closely together to utilize each other’s body temperature. After feeding in the evening, the bats congregate in their nighttime roosts. Big Brown bats will hibernate during the winter months in a cool, dark, secluded place like an abandoned mine or cave. These bats prefer insects with aquatic life stages so roosts will often be found near water.

Big Brown bats feed on insects: primarily beetles but also mosquitoes, gnats, mayflies, moths, dragonflies, lacewings, and wasps. The bat uses echolocation to find its prey in the dark then tucks it into a pouch made with its wing. Once it is trapped, the bat will grab the prey and eat it. Big Brown bats, while pesty if roosting in manmade structures, can be greatly control garden pests. Male Big Brown bats have been known to eat as much as half their body weight in a night and lactating females more than their body weight.

The Big Brown Bat’s Circle of Life

From November to March, Big Brown bats are in breeding season. After breeding, the bats will form nursery colonies which consist of only mother and baby bats. These colonies may contain up to 600 bats. Females give birth to one or two babies at a time. The young Big Brown bat will latch on to its mother and remain there until it is ready to fly in about 3 weeks. Mother Big Brown bats care for their young and even communicate with them using high-pitched squeals. Male Big Brown bats do not participate in raising the young.

The Big Brown bat will live over 10 years.

Big Brown bats and Humans

We make crafts with their shape and hang fake ones up at Halloween to scare people, but in reality, there is nothing scary about the Big Brown bat. They rarely come in contact with humans and indeed prefer not to. Although the issue of rabies has been greatly exaggerated in bats, there is still a small percentage of bats that carry the disease. More people die each year from dog attacks, bee stings, or by lightning strikes than from a rabid bat attack. The Big Brown bat has been implicated in only one case of rabies transmission from bat to human.

Professional Big Brown bat Control

Professional control of the Big Brown bat is done using a combination of exclusion methods and should be employed if bats have actually entered a structure. The Big Brown bat is most common in North America and the most likely to roost in manmade structures. For this reason control of these bats using measures to move their roosts elsewhere has been most effective. Professional exclusion of bats is most often accomplished in a series of steps, and can take a significant amount of time, depending on where the bats are in their mating and birthing seasons:

  • Observation: A professional will evaluate the structure for all possible entry points and roosting sites. Observations are done at night to learn about the bat’s entrance and exit habits.
  • Sealing: Any cracks, gaps, or holes in a structure will be sealed, preventing the bats from getting back in to the building. Some primary access points will be left open for bats to get out of the building, but sealing up all secondary entry and exit points will ensure that the bats have no alternate entry points.
  • Bat Proof! Exclusion of bats is not typically done while female bats are caring for their young. Eliminating the mother could cause young bats to die, which creates a cleanup problem later on. For this reason, exclusion is usually done in the summer or early fall. Exclusion is typically done by installing one or more vents to round up the bats and direct them away from structures.
  • Cleanup: If bats have been roosting in a structure for any amount of time, there are likely large amounts of bat droppings and other debris. Most professionals will take care of this mess as part of their service. The guano and urine of a bat tends to attract nasty pests like cockroaches, ticks, and mites. All areas where bats have been thought to reside should be thoroughly scrubbed and sanitized.
  • Granular Repellent such as Bat-A-Way can also be an effective but humane way of keeping bats out of buildings. It is sprinkled around potential entry and exit points or in places where bats are known to roost. Once such a repellent is used and areas where the bat were previously thought to be roosting, clean up the guano and other debris left by the bats and install mesh screens to keep them from coming back.

DIY and Green Solutions for Big Brown Bat Control

Although bats can be quite the pest if roosting in or around a building, they can also be a beneficial part of a garden ecosystem. For this reason, it is best that control measures are taken that are also sensitive the bat population. Any do-it-yourself efforts should be employed with extreme caution. Always wear protective gloves and a mask if coming in direct contact with the bats. Bat guano is known to contain bacteria dangerous to humans, and a small percentage of bats are known to be carriers of rabies.

  • Bat Valve: Also used by professionals, a bat valve or cone is a one-way opening that is installed in the entry and exit points of a bat roost. This leaves an exit for the bat, but the valve is designed so that it cannot get back in. This should only be used after smaller alternate openings are identified and securely sealed. A bat valve or bat cone can be purchased at home improvement store and installed by yourself.
  • Netting: Position yourself outside and keep watch in the evening hours when bats are coming and going from their roosts. Once entry and exit points are identified, set to work sealing up small entrances like cracks using a caulking gun. Leave at least one large entrance/exit from which bats can come and go. Using bird netting, secure the hole at the tops and sides of the entry point, leaving the bottom open (so bats can still come out). Most of the bats will leave their roosts at night, so a couple hours after starting the installation of bird netting around entry and exit points seal up the netting, keeping the bats out. This technique is best done night to night, using a combination of a granular pellet like Bat-A-Way and the netting. Keep doing this until there are no more bats in your home. If a bat does enter your home, trap it under a coffee can or cardboard box and slip something rigid like cardstock underneath. Release the bat outdoors.
  • Install a bat house: Now this seems counterproductive, doesn’t it? Actually, installing a house away from your own in a cool, dark spot can keep bats away from your home and also provide a place to live after excluding them from roosting sites.

The Big Brown bat has a far-reaching habitat and can be extremely destructive to homes and other structures. A professional can locate, remove, or re-locate a bat roost, but some steps in the process can be done on your own.