Why Are There Bats in My Attic? A Homeowner’s Guide

Wildlife Pros Editorial Team · Published August 5, 2026 · Last updated August 16, 2026 · 14 min read

When clients ask us why they have bats in their attic they usually mean it in two ways, simultaneously.

The first is why bats go into attics generally. And the second is why did bats choose their attic specifically. Though many of them have read about the subject online, they are still confused and have a lot of followup questions about both sides of this question: What are they doing in there? How long will they stay? Will they leave if I don’t do anything? Why did they choose my house? Is something wrong with my construction?

One common phrase some clients use is “I’ve been living in this house for ___ years and have never had bats before, why do I have them now?” The purpose of this guide is to give you the same education our clients receive when they call us to consult.

During Warm Months It’s a Maternity Colony

The bats over your ceiling during the summer are almost entirely female, and they are there to give birth and raise their young. Females gather in the spring to form a maternity colony. They commonly choose attics because of the heat. Female bats prefer hot temperatures. The optimal temperature window varies depending upon the species, with some living in temperatures up to 104 degrees comfortably.

If a female’s body temperature falls too low, she needs to enter a torpor state to survive, which is a deep energy saving sleep, similar to a mini hibernation. This leads to reduced milk production and risks to her babies. The pups raised in suboptimal temperatures can develop behind schedule, fly later, and go into their first winter smaller than they should be. A warmer attic allows them to develop faster and leave stronger. Females raise their young together not only to have better protection from predators, but also to share body heat. They will pack tightly together in a small space, a strategy known as clustering, to magnify the warmth. When outdoor temperatures fall at night or during a summer storm, the core of the cluster stays hot.

There is a limit to how much heat each species of bat is comfortable with. When an attic gets too hot for them, they will sometimes climb down into wall cavities where it is cooler, or move toward the entry points to sleep where fresh air is available. Uncomfortably hot bats sleeping near the exterior entry holes are a primary reason why homeowners might see bat guano falling down the side of a house from the roof line.

Males spend the summer elsewhere, alone or in small groups called bachelor colonies. They prefer cooler areas and do not like the excessive heat. They sleep in areas where the temperatures allow them to conserve energy through the day by entering torpor. The females also take the better feeding ground, because they need the certainty of ample food more, so the males will range further out when there are not enough insects to support both.¹

Bats Are Devoted Mothers

Pups arrive in early summer and cannot fly for their first several weeks. Though many bats give birth to one pup per year, our common attic species in Middle Tennessee usually carry twins.² A colony adding two young per female per summer grows fast.

Bats are mammals, and exhibit extraordinary dedication and care for their babies. They wrap their pups in their arms tightly to keep them warm. Some forms of tree roosting bats will hold them while they hunt.

They have specific vocalizations for their babies that are different than how they speak to other adults, a sort of “baby talk” similar to humans. Cave dwelling bats leave their babies in a communal nursery area while they go to hunt. But when they return, despite how many babies are in a nursery area, she can locate her exact baby by its own vocal signature and scent.

A female nursing a pup can eat more than her own body weight in insects in a single night, because she needs the calories to produce sufficient milk.

They are incredibly devoted and bat biologists call them “supermoms.”

By late summer the young are able to fly, though they are not highly skilled at it yet. The females begin to focus on putting on fat for the winter. They will also begin taking their juveniles to temporary smaller roosts nearby, where the young start learning to find the best hunting grounds and execute more skillful hunting maneuvers.

Homeowners report noticing bats more often this time of year, since the population that is out flying has grown greatly, and since the juveniles who are practicing their flight lines tend to be more visible. Pups who are late bloomers tend to be particularly disadvantaged, as they begin flying later and miss out on some of this important training, as well as the opportunity to put on sufficient weight for the winter.

Return of the Bachelors: Swarming, Migration, Hibernation

Late summer and early fall is when male and female adult bats begin to meet again, typically in a process called swarming. This is where males and females mingle and find mates. The process is different depending upon whether a bat is migratory and where they stay for the winter. Some bats meet at cave entrances and other neutral sites. For other species, the males will come and swarm at the buildings or structures where the females have been staying.

In the Fall, bats begin making their preparations for the winter. Most species of hibernating bats have both the males and the females sharing a roost during this period.

Non-migratory resident bats, such as the Big brown bats, typically stay exactly where they are. This means that if a homeowner has a maternity colony of Big brown bats in the summer, it is very likely they have a colony of hibernating Big brown bats in their home during the winter.

Whether they are a hibernating bat or not, migratory bats will begin making the journey to their winter areas around this time. Some bats, such as the little brown bat, make a journey to winter caves to hibernate. Some migratory bats, such as Evening bats, migrate south for the winter and are thought to remain active.

Either way, in the Spring the bats will return to the same attic they were in the year before to continue the cycle.

But Why Did They Choose MY House?

Bats often look for shelter in areas where there is an ample supply of food, and a water source within a comfortable range, typically a quarter mile. In general a bat eats 50%-100% of its body weight per night in insects. A lactating female may need to return to a water source many times in a single night, as they require more water than non-reproductive bats. Any home that can meet these immediate needs is a potential target for a roost to develop. Since bats will return to the same roosts year after year until something disrupts that process, many homeowners with a home in a desirable area may not have had bats in the past simply because they have never needed to try.

However there are many factors that can send bats looking for new homes. For example, when a roost has become overcrowded, some bats may leave voluntarily to seek a new one.

Additionally, for many bats the habitat is changing around them rapidly. In Middle Tennessee, property development has been booming for years. That development means land getting cleared and houses and buildings going up. Wooded lots come down, old barns and outbuildings come down, spaces that held bats for decades go with them. They find themselves needing to adapt and seek out shelter in these new areas.

Another factor is intentional eviction. When a homeowner hires a company to humanely evict bats from their home, they need to go somewhere. Most often they will search within the territory they have already been living for the next usable roost. Since they are used to living in attics, that is what they will seek out next. It is very possible that the bats moving into your house came from a neighbor a few blocks over.

Is There Something Wrong With My Construction?

Almost every home we have ever inspected has openings that a bat can use to enter. And the majority of them have an abundance of those openings. It doesn’t matter if the house is new or old, well-constructed or poorly maintained. Close to 100% of homes are vulnerable.

This is because bats can get into the tiniest of gaps. If the tip of your little finger fits, a bat fits. The general guideline is 3/8 of an inch. However every bat removal professional has seen firsthand that if the materials that create the gap are flexible, the gap can be even smaller. In addition to existing gaps, new gaps are created over time. Caulking begins to crack. Soffits start to loosen. New construction settles. The materials that the home is built from expand and contract with changing humidity and temperatures over the course of a year. Areas that were tight today may be open tomorrow.

While it is true that homes with serious damage or maintenance issues may need more work and repairs done to keep bats out, a house can be impeccable and still need every square inch of the roof line worked upon to safeguard it properly.

Will They Leave On Their Own?

Big Brown bats will never leave. They will stay year round, hibernating in place through the winter. But even species that migrate for the winter will still return in the spring. They technically do “leave”, but it is only temporary.

Each year the colony size will grow, until the homeowner has them humanely evicted. This is because the previous year’s daughters are now full grown and join the maternity colony to have pups of their own. And the previous year’s sons are now part of the group of bachelors who will be back to swarm and mate in the fall.

Some bat colonies have been known to last for decades without intervention. It is always best to solve a bat problem at the nearest legal eviction window, rather than letting it expand.

Evicting Too Soon Kills the Babies

Mother bats leave every night to hunt and come back to nurse. For the early parts of their lives the pups are helpless and unable to fly. When a homeowner or a company installs eviction devices prematurely, only the mothers can get out. The babies are all left behind to starve. A female bat does not have teeth or jaws built for chewing through wood or commercial sealants. She stays outside, desperate and helpless, while her young die inside. It is a guaranteed death, it is cruel, and it is a crime.³

During maternity season every colony should be treated as though young are present. States are strict about rules and regulations to protect the flightless pups. If any company offers to evict or remove bats during maternity season, they should be immediately reported to that state’s wildlife agencies. These companies can face severe consequences, and may lose their license to remove wildlife completely.

When is Maternity Season (Actually) Over?

Each state sets its own date after which bats can be legally evicted from a home. The goal of this window is to ensure that the most pups possible have learned to fly. These dates vary from state to state, but are typically between August 1 and August 31. Even neighboring states don’t always agree on the precise date at which it is safe to evict. One reason for this is that nature isn’t as precise as we’d wish it to be.

Females give birth over a range of dates, and some pups develop more slowly than others. Whether this is due to weather, insufficient food or some other cause, these late bloomers exist. They rely on their mothers longer, and early evictions within the legal windows can still lead to their starvation and death. Without examining the colony it is impossible to know whether they are present. Sometimes these late bloomers aren’t flying well until mid-August.

Many states who allow early August evictions have protocols in place to attempt to safeguard against this. Some require companies to check in with the head of the wildlife program to consult or receive written permission. Some require companies to check the colony to ensure all babies are flying prior to evicting. But the reality is that it isn’t always possible to do so. Sometimes the colony is in an inaccessible area. Sometimes well-intentioned companies will believe that all the babies are out and flying but they may be mistaken.

For this reason several states move back the date of the window. Some set it to August 15. Maryland sets it to August 31 unless a company applies for a written exemption. As a general rule, by mid to late August all of the pups should be able to fly. For this reason most responsible bat companies will push back evictions until at least the end of August to account for any late bloomers.

A Winter Eviction Kills the Colony

Hibernating Big Brown bats in a homeowner’s attic are living on stored body fat throughout the winter. Waking them up raises their metabolism and burns through fat too quickly. During the winter there aren’t sufficient bugs outside to eat, so if they aren’t able to get back into a hibernating state they will die.

A winter eviction is effectively a death sentence. The colony gets pushed out of a warm building into the cold without food. They are already running on reserves, they are weak, and now they are awake and burning fuel fast. They have to find a new roost immediately, in harsh weather, and then settle themselves sufficiently to hibernate again. The odds of survival are slim.

Tennessee bats are classified as protected wildlife and killing them is against the law.³ Responsible bat companies will never evict bats in the winter.

Occasionally homeowners call with a bat flying around inside their living space during the winter. Bats who wake up from hibernation prematurely are hungry and will sometimes follow the warm airflow into a home looking for food since there is none outside.

A single bat in the home during the winter means that there is a colony inside as well. Call a bat removal specialist to have the bat inside the home captured, and to make a plan to evict the colony in the Spring after they emerge from hibernation, but before they give birth. In the meanwhile common sense strategies inside the home can be taken to ensure bats who awaken early do not enter into the living space again. These strategies typically involve closing up gaps in the sheet rock so that bats who awaken in the walls, stay in the walls.

Another winter call we receive is from homeowners having construction work done inside their homes. Often these homeowners have been told by contractors that they spotted bats in their walls. Those bats are part of a colony that is being disturbed and awakened by the noise and vibrations of the work being done, and sometimes they will crawl to the openings to investigate. Call your local state wildlife agency immediately to discuss whether the work should be halted to prevent further disturbing the colony. Not only is waking the colony dangerous for the bats, but it also puts the workers at risk of encountering disoriented and frightened animals. In most cases, unless the work is a true emergency, it should wait until spring when the bats have been safely and humanely evicted.

Should I Install a Bat Box?

Installing a bat box will never make the bats leave your attic, since they already have a luxurious home of their own. The only way to get them out of the attic is a humane eviction that also seals and protects the structure.

Bats are worth having around, and if you would rather keep a colony on the property, having a safe and suitable place for them to move into is worth trying. Bat boxes should be installed a sufficient time prior to evicting, to give the bats an opportunity to acclimate to them in their environment.

Bat boxes need to meet several criteria to be suitable for a colony. If improperly built or installed they can seriously harm and even kill bats.

To learn more about proper installation, click here to read Bat Conservation International’s bat house guidelines.

How Do I Get Rid of the Bats in My Attic?

The purpose of this guide was to inform and educate you so that you can advocate both for yourself, and for the bats who have moved in upstairs.

Getting rid of bats in a safe and lasting way means hiring a bat removal specialist who sees the full picture. They need to fully understand both the bats and the construction of your house. And they need to offer you solutions that are humane, legal, and effective.

The terms “bat removal” and “exclusion” mean completely different things from one company to the next. The materials each uses to protect the home are different, both in terms of aesthetics and durability. The guarantees are different both in length and in scope. The eviction plans vary drastically, from the humane to the cruel.

Our Bat Removal page covers how the eviction and seal-up work in more detail.

And if you are in Middle Tennessee and would like a consultation about the bats in your attic call (615) 422-5923 and we will be happy to help.

This article is general wildlife information for Middle Tennessee homeowners. Colony size, species, and timing vary by structure. For a specific attic, have it inspected.