Stephanie Richards, PhD, Medical Entomologist
Bats are nocturnal mammals that feed primarily on plants (i.e., nectar, fruit), insects and spiders, so they can be considered beneficial for reducing some insect populations. There are currently approximately 1,300 bat species recognized. Some species feed on small birds, frogs and/or fish.
Notorious vampire bats, consisting of three species total, feed only on blood to survive. These species blood feed on a variety of animals, including reptiles, amphibians, birds and mammals (including humans). The common vampire bat (Desmodus rotundus) is distributed through Mexico, Central America and South America. Scientists have discovered that vampire bat saliva contains effective anticoagulants that are used to prevent clotting during blood feeding.
Bats can range in size from approximately 2 grams (e.g., bumblebee bat) to 2.5 pounds (flying foxes). Most bat species are active at night and use echolocation to locate/capture food. However, there is one bat species (Samoan flying fox [Pteropus samoensis]) that is active primarily during the daytime.
Bat roosts include locations such as caves, cavities in trees and, occasionally, human residences (e.g., attics, chimneys). In tropical climates, bats are active year round. However, in temperate climates, bats can either migrate to warmer areas during colder months or go into hibernation.
BATS AND DISEASE
Bats should be excluded from homes due to the possibility of pathogens being transmitted to humans (either through bite or from aerosolized pathogens in droppings). In the United States, the rabies virus has been associated with animals such as raccoons (highest incidence), followed by bats, skunks, foxes, cats, cattle and dogs (Monroe et al. 2016). When a human is bitten by a rabid animal, that person may become infected with the rabies virus.
The rabies virus affects the central nervous system of victims and organs (e.g., skin, heart). After an incubation period of a few weeks to a few months (typically), the rabies virus infects the salivary glands of potential vectors and can be transmitted to victims via saliva at the bite site. There are post-bite rabies vaccines available for humans, and these therapies increase the chances of survival of a rabies virus infection. Although there is a low incidence of bats transmitting the rabies virus to humans (one to two cases/year in the United States), rabies has been detected in all continental U.S. states. More information on rabies can be found through the Centers for Disease Control and Prevention.
Bats are also associated with other diseases, such as Marburg hemorrhagic fever, Ebola hemorrhagic fever, Nipah virus encephalitis, Nipah virus disease, histoplasmosis and diseases caused by coronaviruses and Lyssaviruses.
KEEPING BATS OUT OF BUILDINGS
In some instances, bats may accidentally fly into homes where openings exist. In other cases, destruction of natural bat habitats due to land development may encourage bats to seek shelter elsewhere (e.g., human residences).
If you suspect you currently have a bat issue, your home should be inspected for possible bat entry points. Any openings larger than one-fourth inch by one-half inch should be sealed appropriately with caulk, screens, stainless steel wool or other methods. Chimneys can serve as an entry point for bats and can be capped, if necessary.
In some instances, bats have come into contact with humans at summer camps where cabins may not be sealed properly. In open-air buildings that cannot be sealed, mosquito nets can be draped over beds to minimize the possibility of bat exposure (as well as mosquito exposure).
If you suspect you have been exposed to a bat, a wildlife professional can be contacted to safely capture it, as it may be required for rabies testing. A medical professional should be consulted to provide assistance, as needed. Keep in mind that bats are protected and regulated, so make sure to check with your local authorities before exclusion or other services are performed.
Monroe BP, Yager P, Blanton J, Birhane M, Wadhwa A, Orciari L, Peterson B, Wallace R (2016) Rabies surveillance in the United States during 2014. Journal of the American Veterinary Medical Association 248:777-788. https://avmajournals.avma.org/view/journals/javma/248/7/javma.248.7.777.xml