Yep. Amazing little engineers they are. They lie in wait, fully buried at the bottom of that conical trap. The angle of the wall is such that any disturbance causes an avalanche, and the monster at the bottom of the pit starts tossing up more sand so that the hapless ant or other small insect which caused the initial disturbance is avalanched right down into those fearsome mouthparts.
If they are somehow fooled by some giant godlike creature disturbing their traps for amusement, they can rebuild the trap in moments once the giant has become bored and moves on to torment other small beings.