Antlions like fine sand or silty soil so they can make perfect pits to trap ants. They hate water so you usually find them in sheltered places where rain can't flood their pits. They are often found in clusters which makes them easy to spot. You can also find that at beaches besides trees or shelters. Try spotting them when you go fishing at the beach.
If you have the time, just hang around and watch how the ants fall into the pit and how the antlions tackle them. Be sure not to step on their fragile pits, young antlions make very small pits to be easily spotted.
Enjoy
Antlion Pits
Antlion Larvae
Cocoon of Antlion
Adult Antlion
Video of an antlion pit in action