Attics, Cellars, and... Bats
If you’re lucky enough to live in an older home—or simply a house with an attic, basement, or crawl space—you may already have a few hidden wildlife habitats right under your roof. Quiet attics, cool basements, storage cellars, and other little-used spaces often provide shelter for a surprising variety of beneficial animals that have adapted to living alongside people.
Far from being a nuisance, bats are among the most valuable wildlife neighbors you can have. They are voracious nighttime insect hunters, consuming thousands of mosquitoes, moths, beetles, and other flying insects in a single evening. Healthy bat populations help keep garden pests in check and reduce the need for chemical insecticides. Despite old myths, bats do not intentionally fly into people’s hair, and they are generally shy animals that avoid human contact whenever possible.
Attics can be especially attractive to bats because they are warm in summer, relatively undisturbed, and often connected to the outdoors through small vents, gaps beneath rooflines, or tiny openings around eaves. Many North American bat species use these spaces as daytime roosts or maternity colonies during the warmer months. If an attic is separated from the living area of the house but still allows bats to come and go through small exterior openings, it can provide valuable habitat without bringing wildlife into your home.
Among the bats most commonly found around homes in North America are the Big Brown Bat, a year-round resident in much of the United States that frequently roosts in attics and barns, and the Little Brown Bat, which often forms summer nursery colonies in older buildings. In warmer regions, species such as the Mexican Free-tailed Bat may gather in enormous colonies beneath bridges, inside abandoned buildings, or occasionally in attics, emerging at dusk in spectacular flights to feed on flying insects. Several species of Myotis bats also use barns, sheds, and secluded buildings during the summer before migrating or hibernating elsewhere for winter.
Many bats depend on old buildings because natural roosts such as hollow trees, rock crevices, and caves have become less common in developed landscapes. If bats are using a part of your home that is isolated from living spaces and not creating health or structural problems, allowing them to remain can make a meaningful contribution to local biodiversity. However, if bats are roosting inside occupied areas of the home, exclusion should always be carried out humanely and only after young bats are capable of flying, following recommendations from your state's wildlife agency.
Dark indoor spaces can also support other useful creatures. One example is the darkling beetle (Tenebrio molitor), whose larvae are commonly known as mealworms. Mealworms develop in dry, dark places where they feed on grains and other plant material. They are widely raised as nutritious food for bluebirds, wrens, chickadees, robins, reptiles, amphibians, and many other insect-eating animals. Home gardeners who raise mealworms should keep them in enclosed containers with proper ventilation and clean bedding, making them an easy, year-round source of high-quality food for backyard wildlife.
Not every hidden corner of a house needs to be perfectly sealed or brightly lit. With thoughtful management, attics, outbuildings, and other undisturbed spaces can provide refuge for bats and other beneficial species while allowing people and wildlife to live comfortably side by side.
Some bat species are closely associated with natural caves, while others readily adapt to buildings, barns, bridges, and even homes. In fact, the smallest bats are among the species most frequently found in American towns and cities, where they often hunt insects around porch lights, streetlights, and illuminated parking lots. Unlike larger cave-dwelling species, they do not always require large enclosed spaces. A narrow gap behind siding, beneath roof flashing, inside expansion joints, or under loose roofing materials can provide all the shelter they need.
In much of the United States, bats remain active well into the fall, with many species delaying hibernation until colder weather arrives. If you happen to locate a winter hibernation site—such as a protected cave or abandoned mine—it is not unusual to find dozens or even hundreds of bats gathered together. Because hibernating bats are extremely sensitive to disturbance, these sites should always be observed from a distance. Waking bats during winter forces them to burn precious fat reserves they need to survive until spring.
Although bats are among the best-known animals to use sheltered winter refuges, many other creatures spend the cold months in a similar state of dormancy. One of the most fascinating examples is found among butterflies that overwinter as adults, including several species of anglewings (Polygonia spp.), mourning cloaks (Nymphalis antiopa), and question marks (Polygonia interrogationis). Their upper wings display vivid oranges, yellows, and blues, but when the wings are folded shut, the undersides resemble weathered bark or dead leaves so closely that they almost disappear against tree trunks.
If you discover one of these butterflies resting through the winter, resist the temptation to handle it. On a mild day—or with the gentle warmth of sunlight—it may briefly become active before settling back into dormancy. Watching this transformation offers a remarkable glimpse into one of nature’s most effective camouflage strategies.
BATS! • Species Most Closely Associated with Human Structures
The following North American bats are among those most frequently found in buildings, bridges, barns, and other human-made structures.
| Common Name | Scientific Name | Typical Habits | Preferred Roost |
|---|---|---|---|
| Little Brown Bat | Myotis lucifugus | Common in summer colonies in attics, barns, and buildings; females form large maternity colonies. | Buildings, attics, tree cavities |
| Big Brown Bat | Eptesicus fuscus | One of the most common urban bats; often remains in buildings year-round in milder regions. | Buildings, wall voids, attics |
| Mexican Free-tailed Bat | Tadarida brasiliensis | Forms enormous colonies beneath bridges, in buildings, and in caves throughout the southern U.S. | Bridges, buildings, caves |
| Evening Bat | Nycticeius humeralis | Frequently roosts in buildings and tree cavities across the Southeast. | Buildings, tree cavities |
| Tri-colored Bat | Perimyotis subflavus | Roosts in trees during summer and caves during winter; occasionally found in buildings. | Tree foliage, caves |
| Yuma Myotis | Myotis yumanensis | Often occupies buildings and bridges near rivers and lakes in western North America. | Buildings, bridges |
| Pallid Bat | Antrozous pallidus | Uses rock crevices and buildings in arid regions; often forages on the ground for insects and scorpions. | Rock crevices, buildings |
| Rafinesque’s Big-eared Bat | Corynorhinus rafinesquii | Prefers abandoned buildings, barns, and hollow trees in the southeastern United States. | Abandoned buildings, hollow trees |