Like a shadow rising up from the bowels of the earth, a cloud of innumerable small black shapes stream through the twilight. They are bats, thousands upon thousands of them emerging to hunt insects as they do every night here in eastern Thailand.

Along the rolling landscape, low and craggy cliffs rise from rice and manioc fields. Over eons the limestone outcrops of these cliffs have been eroded into labyrinthine tunnels and caves. This unusual karst topography has created the ideal refuge for many thousands of bats. Feeding on an ample supply of insects in this agricultural region, they act in many ways as a natural form of biological pest control. Revered and respected by villagers, some of the bat caves are even honored by monks. Below one monastery, giant statues of the Buddha seated in the lotus position gaze out of the inky darkness. Overhead, hundreds of bats chirp and jostle in their roost, sleeping away the day in anticipation for the night hunt.

On the edge of Khao Yai National Park you can visit these caves and watch from the fields as the bats emerge to hunt at twilight. At first, only a faint trickle of black shapes is discernible from the cliffs, but soon a huge and unmistakable river of bats weaves over the fields like a snake. Like one living creature, the bats contort as a school of tiny fish might from the narrow opening of this cave system. At the entrance to the cave, raptors congregate in anticipation of an easy meal. As they dive toward the bats, the line opens and separates before joining together again in a twisting ribbon.

This spectacle occurs for hours every night before the last bats exit the caves. Established in 1962, the second largest National Park in Thailand, Khao Yai is located about four hours from Bangkok in Thailand’s Nakhon Ratchasima Province. Over 2,168 kilometers in area, the park is home to a huge variety of creatures in addition to the many bats. It is a UNESCO World Heritage Site.