The Los Angeles night sky is often patrolled by a common, yet unobserved, resident: the bat. Los Angeles County provides a suitable habitat for a variety of bat species, which thrive in both wilderness areas and the dense urban core. These nocturnal mammals are prevalent throughout the region, often utilizing man-made structures for their daytime rest. Understanding the local bat population offers insight into the city’s complex natural dynamics.
Common Bat Species in Los Angeles
Los Angeles is home to over a dozen bat species, but three are common and noteworthy. The Mexican Free-tailed Bat (Tadarida brasiliensis) is the most frequently detected species in the metropolitan area, known for its small size and long, narrow wings. Its tail extends noticeably beyond the edge of the tail membrane, and it has reddish to dark brown fur. These bats are fast flyers, capable of reaching speeds up to 99 miles per hour in horizontal flight.
The Western Mastiff Bat (Eumops perotis) is the largest bat species in North America, with a body length up to 7.5 inches and a wingspan exceeding 22 inches. It is identified by its prominent, large ears that join across the top of its head, and its chocolate brown fur. The Pallid Bat (Antrozous pallidus) has pale, yellowish-brown fur and disproportionately large ears, nearly half the length of its head and body. Unlike many other bats, the Pallid Bat has large eyes and a distinctive blunt snout.
Urban Roosting Habits
Los Angeles bats have adapted their roosting behavior to a landscape dominated by human construction, utilizing structures that mimic natural cliffs and caves. The Mexican Free-tailed Bats often establish large colonies within the narrow, sheltered spaces beneath freeway overpasses and bridges spanning the Los Angeles River. These man-made crevices offer protection from predators and the weather, which is important for maternity colonies.
Other species use features found on residential and commercial buildings. Bats frequently roost in attics, wall voids, or behind the eaves of houses. The Pallid Bat and Western Mastiff Bat may also utilize natural features like rock crevices in canyons and the loose, dead fronds of palm trees. The Mastiff Bat requires a high roost location, typically 15 feet or more above the ground, because its large size necessitates a clear vertical drop to achieve liftoff.
The Ecological Role
Los Angeles’s bat population provides environmental benefits through their role as nocturnal insectivores. Nearly all local bat species feed exclusively on insects, consuming large quantities of moths, beetles, and mosquitos each night. A single bat can consume up to half of its own body weight in insects during a night of foraging.
This makes them an effective form of natural pest control, a service that saves the agricultural industry billions of dollars annually by reducing crop damage and the need for pesticides. The Mexican Free-tailed Bat focuses heavily on moths, which are often agricultural pests. The Pallid Bat even gleans larger prey, such as scorpions and ground crickets, directly from the ground surface.
Safety Guidelines and Humane Exclusion
Interacting with bats requires safety measures due to the risk of rabies transmission. Although less than one percent of bats in the wild carry rabies, 10 to 15% of bats submitted for testing in Los Angeles County are found to be positive, as these are usually sick animals. A bat found on the ground or flying during the day should never be touched with bare hands. If a bat is found inside a home, it should be safely contained and reported to local public health officials for rabies testing, as their small teeth can leave unnoticeable bites.
If bats are roosting in an attic or wall space, it is illegal to injure or kill them, making humane exclusion the only solution. This process involves installing a one-way exclusion device that allows bats to exit the structure at night but prevents them from re-entering. Exclusion should not be performed between May and August, which is the maternity period when flightless young may be trapped inside. Once the bats have left, the entry points must be sealed, and any accumulated droppings, or guano, should be safely removed by a professional, as guano can harbor mold and disease.