Dear WW: the Ant lion larva that I used to think was some kind of spider has to find
sand similar to what would be used in an hour glass. I don't know how it makes the
conical pit, but it is out of sight in the bottom, until an ant makes the mistake of
taking a shortcut across pit. The ant lion senses the disturbance of the grains of
sand, and digs out slope below the ant, until ant falls down low enough the ant lion
can grab it and pull it out of sight to eat it. All you see is the surface of the sand
being mysteriously made for fall down the slope. I never had patience to stick around
to watch ant lion rebuild the steepness of the slope, which is critical, otherwise ant
could escape.