Antlion Swarmer

Nothing summons them. On the surface they need naturally generated desert walls nearby and they show up during sandstorms, so mining those background walls out around a desert base stops them appearing there permanently. That is worth an afternoon once. The underground desert is the other home, and there you cannot build the problem away.

Everything else in that biome runs along the floor, so whatever footing you set up for the ground fight is wrong for this one. It flies, it closes on a diagonal, and it will follow you into a shaft you dug as an escape route. There is a small version and a large one, and the difference in incoming damage is worth checking before you commit.

Its attack goes down in Expert Hardmode instead of up, which is backwards for an enemy of its tier.

It is drawn from the adult stage of a real antlion, which is why it looks nothing like the Antlion buried underneath it. Those are the larvae. It also picks up a faint afterimage once it hits full speed.