These pits were dug by antlions, the larval stage of an insect that winds up looking similar to a dragonfly. The antlion larva has short, stout body with an enormous pair of hollow pincers that are used to grasp prey and suck out all of the body juices.

The antlion digs its pit by moving in a spiral pattern, scooping up sand and throwing it with its pincers. The nearer it gets to the center of the spiral, the deeper the pit gets. Because the sand is thrown upwards, it forms what is known as an angle of repose. That means that it is piled up as steep as it can get and still be stable. Any disturbance will cause a tiny landslide, so an ant or other creature that walks to the edge of the pit winds up falling to the bottom. If it manages to escape being caught, the antlion will toss sand up the sides of the pit, causing another slide to bring its prey back to its waiting jaws.