SIGHTS LIKE THIS are one of the truly great wonders of the world. As Mexican free-tailed bat colonies leave their caves each summer evening to go out and feed, the sky is filled with bats and the sound of thousands and thousands of wings softly beating the air. Some colonies have so many bats that the emergence may go on for more than three hours. Eventually, the colony disperses, and the bats spend much of the night on the wing, covering thousands of square miles of surrounding countryside, eating countless insects, many of which are agricultural pests.

PHOTO BY MERLIN D. TUTTLE