Urban Legend: Phlegm Mites
Another improbable legend:
Tales of phlegm mites, tiny parasites mainly preoccupied with the consumption of mucus, are common in elementary classrooms. The problem is said to begin when a chronic nose-miner – the tales often use the name Katie or Kathy – unknowingly leaves a green deposit beneath their fingernail. At some point during the child’s muck-handed schoolyard explorations, the mites discover the tempting goo and dig in.
The trouble begins when the finger returns to her nostril.
The unfortunate goes to bed that evening complaining of a persistent itch, and her unsuspecting parents attempt to placate her with some nasal decongestant – unbeknownst to the family, the mites frenzy at the introduction of the chemicals, (and at their suddenly decreasing meal supply.) By morning the tiny insects have eaten through her flesh, creating a large, red and ragged gap.
In other versions of the story, the nose is consumed entirely, leaving only protruding bone.
– source