An Alp-luachra is an evil, greedy fairy from Irish mythology.
Alp-luachra are completely invisible
When a person falls asleep by the side of a stream, the Alp-luachra appears in the form of a newt and crawls down the person's mouth, feeding off the food that they had eaten. Douglas Hyde's Beside the Fire tells of how a person who got rid of the Alp Luachra are eating large amounts of salted meat without drinking anything. He then went back to the stream and fell asleep with his mouth open, in which the Alp Luachra jumped into the water in thirsty desperation.