Wisps are ethereal creatures that are used by wispmothers to lure hapless adventurers in before joining their wisp "children" in direct combat.
Wispmothers are amongst the most powerful and dangerous creatures in Skyrim, and should be avoided until your character is at a higher level. In addition to great perception (rendering your Sneak skill useless) and wisp satellites, it can spawn an infinite number of Shades (clones) which don't disappear on their own over time (but will die on one hit). Wispmothers tend to attack with frost, and appear to be more vulnerable to fire than other elemental attacks. When a wispmother is killed, all remaining wisps will drop dead and turn into ball-like objects which yield Glow Dust when collected.