Manes are frequently generated in large groups.
Manes are very weak and slow, although their three attacks are more than their ostensibly more difficult relative, the lemure. Individually, they are usually very easy to defeat for all but the weakest of characters; however, swarms of them can overwhelm weaker characters since their three attacks can hit for up to 10 HP total per manes.
These will likely be the first set of monsters where getting into a corridor or door is employed as a tactic; this prevents more than one of them from approaching at a time, making dispatching them much easier.
In Roman mythology, manes (MAH-nays) are the spirits of the dead. The word manes is Latin, and has a singular form, manis, but the singular is not used for the meaning specific to these spirits; in English the word has no singular, and so NetHack just uses manes for the singular as well. Compare lemure.
The gnats of the dungeon, these swarming monsters are rarely