Encountering a bat inside a home is startling. While these nocturnal mammals are beneficial to the ecosystem, primarily for their consumption of insects, their presence in living spaces is usually accidental or a sign of a structural issue.
Primary Reasons for Indoor Entry
Bats enter homes for specific reasons, often depending on the time of year. Accidental entry is common during warmer months when a bat might inadvertently fly through an open window or door while hunting insects attracted to outdoor lighting. They use echolocation to navigate, but once inside an unfamiliar space, they can become confused and unable to find their way out quickly.
Bats also seek stable roosting locations. During the spring and summer, female bats look for warm, protected areas, such as attics or wall voids, to establish a maternity colony and raise their young. The heat in an attic is favorable for gestation and milk production.
Bats seek refuge seasonally during the fall and winter. As temperatures drop, they look for cool, sheltered places to hibernate, and a house offers a protected environment. Big brown bats may be found in living spaces during a winter thaw when they periodically wake up and seek water.
Immediate Steps If a Bat is Inside
If a bat is actively flying in a room, remain calm and prioritize safety. Never attempt to catch or handle the bat with bare hands, as any mammal can transmit disease through a bite.
Encourage the bat to leave on its own. Contain the bat to one room by closing all interior doors and then opening a window or exterior door to the outside. Turning off the lights can help guide the bat toward the exit, as they navigate toward darkness indoors and light outdoors.
If the bat has landed and is resting, use a safe removal technique. Place a small container, like a coffee can or shoebox, over the bat and then slide a piece of stiff cardboard underneath to trap it. Carry the covered container outside and release it gently onto an elevated surface, like a tree trunk, as bats need height to take flight.
If the bat was found in a room with a sleeping person, a small child, or a pet, the bat must be safely captured and submitted for rabies testing. This is necessary even if no contact is suspected, because a bite mark may not be visible.
Preventing Future Entry
Preventing bats from re-entering your home involves exclusion. Bats can squeeze through surprisingly small openings, sometimes as narrow as a half-inch wide, meaning a thorough inspection of the building exterior is required.
Common entry points are often found along the roofline, including gaps in the eaves, soffits, and fascia boards, as well as openings around chimneys, vents, and loose flashing. These small cracks and gaps should be sealed using caulk, weatherstripping, or hardware cloth.
For a known active entry point, install a one-way exclusion device, such as a bat cone or netting. This allows the bats to leave at dusk but prevents them from re-entering. Leave this device in place for several days to ensure all bats have successfully exited the structure.
The timing of exclusion is a regulatory and ethical consideration, as bats are protected species in many areas. Exclusion must be avoided between late spring and early fall, which is the maternity season, to prevent trapping non-flying young inside where they would starve. Waiting until late summer or early fall, after the young are capable of flight, ensures the entire colony can successfully leave before the entry points are permanently sealed.
Health and Safety Concerns
The primary health concern related to bats is the potential for rabies transmission. While the overall infection rate in the bat population is low, typically less than one percent, bats are the most common source of human rabies cases in the United States. Transmission occurs through a bite or scratch, and because rabies is fatal once symptoms appear, any direct physical contact necessitates immediate medical attention and testing of the bat.
Another concern is histoplasmosis, a respiratory disease caused by inhaling fungal spores found in bat guano, or droppings. This risk is associated with large accumulations of guano that have dried in damp, enclosed spaces like attics or old buildings. Any cleanup of significant guano deposits should be done with proper protective equipment, including a respirator, to avoid disturbing and inhaling the spores.