What are these munchkins doing in my basement and how did they get there?

I woke up today to a bunch of little munch kins running around in my basement. im not sure why or what they are doing... all i know is that they seem to be building something, what i am not sure, all i know is that they are very annoying and they wont get out, i took a can of hairspray and a lighter then i killed a couple of them, i even used it as a grenade so to speak, all i got was a empty fire extinguisher... why are they here... what are they doing here... and how do i get rid of them.