For some time rumors had been trickling out of Puerto Rico. Not political rumors, or gossip, but reports of a type of boa constrictor that was reputed to prey on bats. The Puerto Rican boa had apparently often been found near cave entrances and in hollow tree trunks where bats were known to roost. These rumors remained just rumors until 1982, when herpetologists visited the Cave of the Boas eight times to observe first-hand the behavior of these remarkable reptiles.

The cave entrance is approximately 15 feet wide and 6 feet high. Large aerial roots of a number of trees form a kind of lattice-work around the entrance. Upwards of five creepy crawlies were observed lurking by day in crevices amongst the roots. When dusk fell, the boas slithered from their nooks and crannies, and coiled around the tree roots. Then, lo and behold, the herpetologists were treated to quite an unusual sight. The boas suspended themselves from the tree roots up to three quarters of their length, directly in the path of emerging bats. Usually at night about seven snakes could be seen swaying silently and not so sweetly from their perches. Some boas were observed inside the cave hanging from stalactites.

For about fifty minutes, beginning at sunset, about 30,000 bats dashed gracefully out through this opening into the dark outside world. Some of them didn't quite make it. Somehow, the boas were able to intercept and hold onto some of the hapless, cute little creatures. Within sixteen minutes, any such bats apprehended by the suspended slitherers were constricted and swallowed.

As soon as the last bat emerged from its hidey hole, the reptiles quit their guard duty, and played around until morning. As daylight's rays lit up the sky, they returned to their lairs. How did the Puerto Rican boa learn to hang upside down at the cave entrance at precisely the same time each day? I think we can guess how.