Bats are the only mammals capable of true, sustained flight, a trait that has allowed them to colonize nearly every corner of the globe. This extraordinary ability is powered by wings formed from membranes of skin stretched between elongated finger bones and the body. With over 1,400 species known worldwide, bats make up roughly one-fifth of all classified mammal species, second only to rodents in diversity. Their size ranges from the tiny Kitti’s hog-nosed bat, weighing less than a penny, to the large flying foxes with wingspans extending up to five feet.
Diet and Ecological Role
Bat species exhibit a wide variety of feeding behaviors, generally categorized into three main guilds. The majority of North American bats are insectivorous, consuming massive amounts of moths, beetles, and mosquitos each night. These bats are highly effective natural pest controllers. This insect consumption provides an immense service to agriculture, estimated to save the United States farming industry over $3.7 billion annually by reducing crop damage and the need for pesticides.
Other species are frugivorous (feeding on fruit) and nectarivorous (consuming nectar and pollen). Frugivorous bats play a significant role in seed dispersal, as they excrete seeds during flight, helping to regenerate forests. Nectar-feeding bats are primary pollinators for numerous plants, including those that produce commercial products like agave, bananas, and mangoes. They possess specialized long snouts and tongues adapted to reach deep into flowers that often bloom at night.
Roosting Habits and Associated Habitats
Bats require specific, sheltered locations, known as roosts, for resting, raising young, and hibernation. These roosting sites can be broadly divided into natural and human-made environments. Natural roosts include caves, tree hollows, rock crevices, and the underside of large leaves in tropical regions. Cave environments are particularly important as hibernacula, providing the constant, cool temperatures and high humidity necessary for bats to survive the winter.
Female bats will gather in warmer, protected locations to form maternity colonies for giving birth and raising their single pup. Many species have adapted to use human-made structures, which provide similar stable conditions. These artificial roosts include:
- Abandoned mines
- Old barns
- Attics
- Expansion joints under bridges
The choice of roost is determined by factors like protection from predators, proximity to foraging grounds, and the specific temperature and humidity requirements needed for metabolic regulation.
Health Risks Associated with Bats
While bats provide substantial ecological benefits, they are also associated with certain health risks. Rabies is the most serious concern, as bats are the most frequent source of human rabies cases in the United States. Transmission occurs through a bite or scratch from an infected animal, although the marks can be very small and easily overlooked. The vast majority of bats in the wild do not carry the rabies virus, with infection rates generally less than one percent.
Any bat found indoors, or one that is easily approachable, should be treated with extreme caution and never handled without protection. Immediate medical consultation is necessary if contact with a bat is suspected, particularly if a person or pet was bitten.
Another risk is Histoplasmosis, a respiratory disease caused by inhaling spores of the fungus Histoplasma capsulatum. This fungus grows best in soil contaminated with large accumulations of bat guano, especially in warm, humid environments like caves or attics. Disturbing dried guano in areas of heavy colonization can release the microscopic spores into the air, leading to infection if inhaled.
Coexisting with Bats
Given their environmental value, the goal of managing bats in human-occupied spaces is humane coexistence and exclusion, rather than extermination. When bats find their way into a structure like an attic, the recommended approach is exclusion, which involves sealing all entry points except for one or two. A one-way exit device, such as a temporary funnel or net, is then installed over the remaining openings. This allows the bats to leave for their nightly hunt but prevents them from re-entering the structure.
Exclusion must be timed carefully to avoid the maternity season, typically late spring to early fall, to prevent trapping non-flying young inside. After the bats have left, all openings should be permanently sealed to prevent future occupancy. For homeowners who wish to support local bat populations while keeping them out of buildings, installing a bat house provides an alternative roosting site. Conservation efforts are also focused on threats like White-Nose Syndrome, a devastating fungal disease that has decimated populations of hibernating bats across North America.