What was the source of the threatening image of a black bat-like creature that appeared on the beach as Ralph blew the conch?

The source of the threatening image of a black bat-like creature that appeared on the beach as Ralph blew the conch in William Golding's novel "Lord of the Flies" was a dead pilot who had landed on the island during an air battle and was left hanging from his parachute on a tree. The boys mistook the pilot for a monster and the image of his body combined with the darkness and their fears created the illusion of the terrifying creature.