Bats are the only mammals capable of sustained flight, yet they are often viewed with suspicion due to their nocturnal habits and association with disease. A balanced perspective requires acknowledging the potential hazards they present when roosting in human structures alongside the substantial benefits they provide to the environment. This article assesses the specific risks bats pose to public health and property, details their ecological functions, and provides guidance for safely managing interactions.
Primary Public Health Risks from Bats
The most significant health concern associated with bats is their capacity to transmit the rabies virus. While the disease is rare in humans in the United States, bats are the source for approximately 70% of the fatal infections reported annually. This is often due to the small size of bat bites, which can sometimes go unnoticed by a sleeping person or a child, leading to a delay in seeking treatment.
The vast majority of bats are not rabid; less than 1% of the wild bat population carries the virus. However, any bat found on the ground or acting erratically during the day should be treated with extreme caution, as this behavior can indicate illness. Rabies is nearly always fatal once symptoms appear, making immediate medical attention and post-exposure prophylaxis (PEP) necessary if any contact is suspected.
Another health risk is histoplasmosis, a respiratory infection caused by inhaling the spores of the fungus Histoplasma capsulatum. This fungus grows in soil contaminated with large deposits of dried bat guano. The risk of infection increases significantly when guano in enclosed spaces, such as attics or caves, is disturbed, causing the spores to become airborne.
Symptoms of histoplasmosis are often mild and flu-like, but the disease can become severe, particularly for individuals with weakened immune systems. Cleanup of guano requires proper respiratory protection and safety measures, and should ideally be entrusted to professionals trained in hazardous material removal.
Property Concerns and Direct Physical Contact
When bats establish a colony inside a home, they can cause property damage. The most prominent issue stems from the accumulation of guano and urine within the roosting area, such as an attic or wall void. Bat guano is corrosive, and its buildup can stain ceilings, destroy insulation, and weaken wood structures over time.
The sheer weight of a large guano pile, combined with the structural decay it causes, can sometimes lead to the collapse of ceilings or floors. The strong ammonia-like odor from urine and droppings can permeate the structure, creating a persistent nuisance. Bats may also inadvertently introduce secondary pests, such as bat mites, which can spread throughout the home and cause skin irritation to residents.
The risk of a bat biting or scratching a person is almost exclusively limited to situations where the animal is handled. Bats are non-aggressive and generally avoid human contact, but they will bite to defend themselves if they feel threatened or are unable to escape. Any physical contact requires a medical evaluation due to the difficulty of ruling out potential rabies exposure.
The Ecological Role of Bats
Bats perform services integral to both natural ecosystems and agriculture. Insectivorous bats, which make up the majority of bat species, are highly efficient natural pest controllers. A single little brown bat, for example, can consume up to 1,000 mosquito-sized insects in a single hour.
This consumption of insects, including agricultural pests like corn earworm moths, provides a significant economic benefit. Estimates suggest that bats save the United States agriculture industry over $3 billion annually in crop damage and pesticide costs. This natural pest management reduces the need for chemical treatments.
In tropical and desert environments, many bat species are responsible for pollination and seed dispersal. Nectar-feeding bats pollinate hundreds of plant species, including commercially grown fruits like bananas and mangoes. They are the sole pollinator for the agave plant, which is used to produce tequila. Fruit-eating bats also scatter seeds, contributing to the early growth and regeneration of forests.
Guidelines for Safe Coexistence and Removal
The most straightforward guideline for interacting with bats is to maintain a distance and never attempt to touch or handle them. If a bat is discovered in an occupied living space, such as a bedroom, the primary concern is to contain it for rabies testing if any human or pet contact may have occurred. The bat should be safely captured, preferably while wearing thick leather gloves, and immediately reported to a local health department before it is released.
If bats are roosting in a non-living area like an attic, the only allowable method for permanent removal is exclusion, which uses a specialized one-way device. This device allows bats to exit the structure but prevents them from re-entering, forcing them to find an alternative roost. Exclusion work must be done by professionals and is often regulated by state laws that protect the animals.
Exclusion Timing
Exclusion is prohibited during the summer maternity season, typically from May through August, to avoid trapping flightless young pups inside the structure. Sealing the entry points during this period would result in the starvation of the young and is illegal in many jurisdictions. The most suitable times for performing exclusion are generally the spring and fall months, when the young are old enough to fly and before winter hibernation begins.