One of the most common bats across North America and one of the species most likely to be encountered in attics. They're voracious insect predators — a single big brown bat can eat 1,000 mosquitoes per night.

Native status: Native; widespread across North America

§ Quick facts

SizeBody length 9–13 cm; wingspan 32–40 cm
Weight14–23 g
LifespanWild typically 6–19 years; record 19 years
OrderChiroptera
FamilyVespertilionidae

§ Encyclopedia

The big brown bat is a species of vesper bat distributed widely throughout North America, the Caribbean, and the northern portion of South America. It was first described as a species in 1796. Compared to other microbats, the big brown bat is relatively large, weighing 15–26 g (0.53–0.92 oz) and possessing a wingspan of 32.5–35 cm (12.8–13.8 in).

Source: Wikipedia — Big brown bat Licensed under CC BY-SA 4.0

§ Identification

Field marks. Medium-large bat with brown fur (lighter on belly); broad face; relatively short ears; broad wings.

Similar species. Little Brown Bat (smaller; lower forehead). Other Eptesicus and Myotis species (subtle differences in size, fur, calls).

Voice. Ultrasonic echolocation calls (25–55 kHz, some within human hearing).

§ Diet & behavior

Diet. Beetles, true bugs, flies, mosquitoes, moths — among the largest bat species, can take larger prey than smaller bats.

Behavior. Among the most common bats in North America. Forms large maternity colonies in attics, barns, hollow trees, and bridges — some colonies of 1,000+ individuals. Less affected by white-nose syndrome than many smaller bat species. Single bat consumes 1,000–2,000 insects per night, providing significant pest control value. Echolocation calls 25–55 kHz — within hearing range of some humans (especially children).

§ Range

Throughout North America from Canada to South America

§ Habitat

Forests, urban areas, attics, barns

§ Threats

White-nose syndrome (less affected than little browns but still impacted), pesticides reducing prey, building exclusions during pup season.

§ Conservation status

According to the IUCN Red List, the big brown bat is currently classified as Least Concern.

§ What helps

Install a bat house away from human activity. Don't exclude bats during pup season (June–August). Reduce pesticide drift.

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§ Further reading

§ Sources cited

  • Bat Conservation International
  • USGS National Wildlife Health Center
  • Smithsonian National Zoo
  • IUCN Red List 2018