Does standing still on the sand still summon more ant-lions?
They constantly spawn when you are touching the sand, but only so many spawn at any one time.
If you're planning to touch the sand, it's best to just sprint until you have to slow down (to climb a cliff or something), and then fend off what's chasing you. There won't be very too many to fight.
It's entirely possible to just sprint / run the entire length of the beach, and make it the whole way to the antlion queen boss, with a small horde of antlions on your tail, without taking too much damage. In this scenario, only kill what manages to close the distance.