I first became familiar with ant lions in east Texas around Trinidad, Kerens , Athens, and Corsicana. They made a living digging a conical hole in the sand where the only part of them that was barely visible at the bottom of hole were two long toothed hooks as you can see in the picture.
They would lay in wait for, you guessed it, an ant or any other unsuspecting insect to come tumbling down into their awaiting jaws. At this point, the ant lion, species Myrmeleontidae, would violently shake insect, spraying it with digestive enzymes, sucking all fluid sustenance from its helpless victim.
In order to prevent having to ingest indigestible sand and dirt, the ant lion through evolutionary pressure has no mouth or asshole(more politely no cloaca). Pretty simple, no holes for the sand to come in. The organism can pee, it just can not poop while in its larval state. Waste does build up and is excreted during adulthood when the pressure of the solid waste causes abdomen to rupture creating a much needed poop shoot.
When we were kids, we enjoyed pulling these sand trapping mouthless creatures from the safety of their cone shaped abodes and feeding them to preying mantises. Seemed fair, letting a bigger monsters pick on a smaller monster.