The cave spider, s, is a monster that appears in NetHack. They are capable of hiding under items, taking some players by surprise. Cave spider corpses have a 7% chance of gaining the poison resistance intrinsic.
Cave spiders are often generated in groups; cave spiders generated upon the creation dungeon level always get a random item to hide under.
While not particularly dangerous for the first hiding monsters you are likely to encounter, cave spiders have a somewhat low AC that can make it slightly difficult to hit them. Throwing an item at them will cause them to hide under it most of the time, useful for keeping them at bay and picking them off, or even escaping if the situation warrants it. This can also be put to use in some treasure zoos, where a hiding cave spider can block the door and hem in the other monsters; you can then attack them from range at your leisure, e.g. with a polearm or lance.