Why are ants able to walk on walls and sealings?

You know those bow and arrow kits with an arrow that has a plunger/sucker thing so it sticks to the surface it is fired at? Ant's feet have very many tiny versions of those suckers. You'd never see it with the naked eye but when they put a foot down, lots of tiny suckers keep them welded to whatever surface they are on, even if they are upside down.