As the sun goes down over Stuart Bat Cave in southern Texas, half a million Mexican free-tailed bats spiral into the sky. For a few minutes, the pulsing, chirping cloud blots out the summer twilight in a display that's either terrifying or inspiring. As a backpacker, you should be cheering. That's because a single bat eats 1,000 insects a night. The colony leaving Stuart Bat Cave will consume 5 tons–the weight of a small bus–before dawn.
Bats comprise a diverse mammalian group found on every continent except Antarctica. They are the only mammals capable of flight, and despite their rodentlike appearance, they are more closely related to primates such as chimpanzees. Three-quarters of bat species eat insects like moths and beetles, while a few others feed on fruit, nectar, or small lizards. Only three Central and South American species drink blood from sleeping animals.
To the Bat Cave
Devil's Den State Park, AR
The sandstone crevice caves dotting the Ozark highlands are home to big brown and red bats. In summer, hit the 1.5-mile Devil's Den loop trail around dusk, so you reach the 550-foot-deep bat cave when the creatures emerge. And don't miss Bat-O-Rama XVIII (June 8–10), with hikes and demos planned. (479) 761-3325; arkansasstateparks.com/devilsden
Kickapoo Cavern State Park, TX
Every night from mid-April to mid-September, more than half a million bats fly out of the Stuart Bat Cave in this undeveloped state park 130 miles west of San Antonio. Sign up for a biweekly guided hike to the cave entrance ($5), or explore the nearby hillsides on the park's 14-mile trail network. (830) 563-2342; tpwd.state.tx.us
Pinnacles Nat. Monument, Ca
Located 60 miles southeast of San Jose, this Salinas Valley maze of canyons and spires is home to a nursery colony of Townsend's big-eared bats. From the visitor center, hike the Bear Gulch Cave Trail through a network of talus caves, which formed when house-sized boulders fell into narrow canyons. (831) 389-4485; nps.gov/pinn
Bats are most active from April to September when they're raising their young (called pups) and hunting food. During daylight hours, they can be found roosting in caves, trees, abandoned mines, and under bridges. A special locking tendon in their toes helps bats hang upside down.
Up all night
The best times to see bats are dusk and dawn, when insects are most active, and when darkness protects these flying mammals from enemies like hawks. If you're waiting by a cave for bats to emerge, stay quiet and keep your flashlight off. Texas-based Bat Conservation International has details on bat-watching sites in every state. (512) 327-9721; batcon.org
From October to March, bats in the Midwest and Northeast hibernate in caves, abandoned buildings, and hollow trees. If you discover a hibernation roost, don't shine lights or take flash photos. Awakening a bat in hibernation will deplete the stored energy it needs to survive the winter.
Even from afar, you can distinguish bats from birds by their darting, erratic flight pattern. Bats use their agile wings–lightweight membranes of skin and bone–to perform the acrobatic maneuvers necessary to catch insects in flight.
At night, bats depend on sound waves to navigate and hunt. Using a process called echolocation, they emit high-frequency chirps that bounce off objects in front of them. By measuring the strength of the return signals, bats can determine the distance, bearing, and size of a tree, rock, and even a fluttering moth.