An Alp Luachra is an evil, greedy fairy

Fairy

A fairy is a type of mythical being or legendary creature, a form of spirit, often described as metaphysical, supernatural or preternatural.Fairies resemble various beings of other mythologies, though even folklore that uses the term...

 from Irish mythology

Irish mythology

The mythology of pre-Christian Ireland did not entirely survive the conversion to Christianity, but much of it was preserved, shorn of its religious meanings, in medieval Irish literature, which represents the most extensive and best preserved of all the branch and the Historical Cycle. There are...

. When a person falls asleep by the side of a stream, the Alp-luachra appears in the form of a newt

Newt

A newt is an aquatic amphibian of the family Salamandridae, although not all aquatic salamanders are considered newts. Newts are classified in the subfamily Pleurodelinae of the family Salamandridae, and are found in North America, Europe and Asia...

 and crawls down the person's mouth, feeding off the food that they had eaten. Douglas Hyde

Douglas Hyde

Douglas Hyde , known as An Craoibhín Aoibhinn , was an Irish scholar of the Irish language who served as the first President of Ireland from 1938 to 1945...

's Beside the Fire tells of how a person got back at an Alp-luachra by eating large amounts of salted meat and sleeping near the stream. The Alp-luachra fed upon him, but jumped to the water in thirst.