Louse

A louse, more commonly known by its plural lice, were a type of skin-pest that caused an itching sensation on one's skin.

Species

 * Hell louse: a species of lice that were native to the plane of Malbolge. They had a white carapace and could reach gigantic proportions. They were typically found in that plane's Hair Forest.
 * Wizard lice: a species of magical lice that were native to the land of Zakhara.

Habitats
In Faerun lice were known to be encountered in Cormanthor, the Vast, Thar, Shadowdale. Beyond that they could be found in the Hordelands.

Beyond Toril they could be found on the planet of Krynn, where they often infested the scalps of ogres.

Relationships
Lice often infested the fur of gibberlings, the shaggy unkempt hair of cyclopskin, and padded armor.

The people of the Plain of Horses, due to their peaceful nature, were some of the few intelligent creatures in the Realms who didn't seek to eradicate lice. Instead they merely plucked the pest from their clothes and placed it back on the ground.

Trivia

 * Camping spots infested with lice were one of the many unfortunate things that could occur as a result of the minor curse of a killmoulis.