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October 11, 2019

(Big Brown) Bats in the Attic

By Hogarth's Pest Control

The big brown bat happens to one of the more common species of bat we encounter. We most often find in barns, attics, and other buildings. These mammals play an integral role in the ecosystem of many areas, helping to manage the populations of insects in these locations.

Big Brown Bat Biology

Aptly named the big brown bat is a larger than average species of bat. They have sleek brown fur over most of their bodies. The wingspan of the bat ranges between eleven and thirteen inches, the torso being no more than eight inches long. Female big brown bats are slightly larger than the males; despite their stature, even the largest specimens will rarely weigh above 5/8 an ounce. These bats are know to form maternity colonies, the numbers being far less than the little brown bat, which tends to form large groups.

The biology of the bats offers a variety of communication methods for the mammal; their nasal glands emit different chemical signals, and like other bats, are nocturnal animals, using echolocation while flying, allowing them to identify prey in mid-air.

Big Brown Bat Habitat

The living range of the big brown bat is quite vast; the species can adapt to the climates of most parts in North America, from northern Mexico to Canada. However, the big brown bat is most common in the north half of the USA, with fewer colonies in the southern states (mainly in Texas and Florida). The big brown bat shows a preference for roosting in areas closer to the water; they will also always look for somewhere dark and cool where they can sleep during the day. This means that they will often roost in caves and the attic spaces of buildings, and look for more secluded, quiet roosts for their hibernation.

The big brown bat is commonly a species found in more rural areas, but is highly adaptable and can survive in both urban or suburban areas with gardens and parks where insects are abundant


The big brown bat is an insectivore, eating almost any flying insect it can catch. For this purpose, the bats have 38 small, sharp teeth. Although the bat can catch many of these flying insects in its mouth, it will also net insects with its tail membrane. From there, it can then transfer the food into its mouth, all while flying. All of the bat’s hunting is done during twilight and in the night. Insects such as gnats, mosquitoes, midges, moths, and mayflies are all potential food. An efficient digestive system means that the big brown bat can eat up to 600 insects within one hour! Contrary to popular belief, these bats are not blind; they simply use echolocation to help them catch insects in the dark of night.

The Reproductive Cycle

The big brown bat mating season generally spans September and October, which is the period leading up to their hibernation. Mating usually happens as the bats swarm at the entrances of the hibernation roosts, although it is also known that a male waking during hibernation may also mate with a female during her hibernation. The sperm of the bats then stores until the spring, which is when fertilization happens. The females join large nursery colonies in the spring and give birth to one, sometimes two, young in June—July.

For the first few flights, the baby will often cling to the teat of its mother; although, after a few weeks, will then be left at the colony. After around a month, these young bats wean and become capable of flight; from here, the mother will depart from the nursery colonies. Females are often ready to breed after the first year, while the male will begin mating in the second. The big brown bat’s life can span over ten years in the wild!

White Nose Syndrome

Because of their tendency to roost in colonies, the bat population is particularly at risk of White Nose Syndrome. This is a fungal disease that has killed many thousands of bats in North America. We identify this fungus by the white traces left on the noses of a variety of species of bats (all of which live in caves). This disease has decimated many colonies of the Big Brown Bat.

Infestation Remedies

The most effective and safe method of bat control is an exclusion. This involves the process of sealing, caulking, screening, and/or venting all potential bat entry points on the exterior of the structure to evict the bats and prevent future entry. Removal is often done through the use of one-way exit devices that allow them to leave the structure but not re-enter.


Bat trapping is not a biologically sound method of eviction, one that we at Hogarth’s Pest Control and Wildlife Removal do not use or promote. Call us to set up an inspection of your structure today!

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