The Alp-Luachra, more easily remembered as the Joint Eater, is a parasitic Celtic faerie that lives throughout Ireland. In some legends, they have been described as small humanoids, but the most popular description is that of a small green newt.

Joint Eaters act like newts, for most intents and purposes, therefore they would logically share the same habitats; streams, ponds, creeks, wet grass, and other bodies of fresh water. Unlike normal newts, however, Joint Eaters are parasitic. To become infected, you must sleep outdoors near their habitat. While you are sleeping, the Joint Eater will crawl down your throat and into your stomach. To decrease resistance Joint Eaters have developed a specialized mucus that acts as a general anesthetic. Anything this mucus touches numbs, allowing the faery to stealthily enter. Ancient Celts used Joint Eaters medicinally because of their mucus. By applying, or ingesting it injuries would swiftly numb. 

Similarly to a tapeworm, once established in your body, the faerie will begin eating large portions of your meals. Unsimilarly, it only eats the pith/quintessence of the food (the nutrients) leaving the mass of the food to be digested and excreted.

The effects of a Joint Eater infestation are felt after a few days. The host initially becomes fatigued and weak. Soon the host will begin to slowly starve. The name Joint Eater most likely originates from the aching joints felt during starvation, being misattributed as being eaten. These symptoms will increase in severity until the host is killed. The faery is unfelt inside its host until it grows substantially from its diet. At this stage, its “wriggling” can be felt by the host. Even if alone, a female will be able to reproduce inside its host. Commonly eight to twelve babies are hatched. This apparently asexual trait may be a form of carrying fertilized eggs until a suitable food source is found. The new babies reportedly make the “wriggling” unbearable, worsening the mental condition of the host. 

Ancient Celts had two popular methods of ridding themselves of these parasites. For either method, it's recommended to have an aide hold the mouth open, and physically restrain those of weaker wills. The first option, which is notably less successful, involves trying to lure out the Joint Eaters. A very savory food would be placed in front of the host, who would keep their mouth open and lay down near it. The intoxicating scent of the food would reach the faeries who would leave their host to consume the food. When crawling out of the host’s throat, the children exit in a large clump. Afterward, the older Joint Eaters leave in single file. The older ones are approximately as fat as your mouth and eight to twelve times longer than the babies. The second, and more successful, method is to starve the Joint Eaters out. The host will eat large amounts of heavily salted meat then drink nothing afterward. Next, the host would lay down next to a large body of water and wait out their parasites or die trying. This method is much more dangerous than the first and should be used as a last resort. The high concentration of salt added to a malnourished body may induce fatal heart attacks.