The Antlion is an enemy found in Deserts during the day, and are also found in Underground Deserts. They remain stationary with their head sticking out of the ground, and will shoot stackable sand at players when they enter their line of sight. They can only launch their projectile at an upwards angle (within about 45 degrees to the left and right), so approaching from lower ground means you will usually be out of their line of fire. They can be rather annoying to less experienced Terraria players.
Because the Antlion creates Sand Blocks as it attacks, sand is technically a renewable resource, although one renewed slowly.
If faced with an incline facing directly upward, Antlions will climb very slowly toward the player. This happens on all versions, and prevents them from burying themselves.
The Antlion's head is the only part that takes/deals damage. Thus, if an arrow is aimed at its body, it will fly through. Likewise, a player that touches the Antlion's body will not take damage.
The Antlion is based on real life Antlion larvae, which dig sand pits as traps for other insects. The antlion will throw sand at escaping prey, causing its victims to tumble down into the center of the pit where the hungry antlion is waiting. When the larvae grow up, they resemble the Antlion Swarmer.
The NPC ID image contains only the head. The body is stored not by an ID, but rather by its name: "AntlionBody.xnb"
The projectiles the Antlion shoots can damage other enemies, not just the player.
"Antlion" is commonly mispronounced as "antillion", when, since it's based on the insect, it can be assumed that one would pronounce it the same as the insect – "ant-lion".
This is one of only two or three creatures besides the player that can place blocks in the world. (The other being the Snow Balla and debatably, the Wall of Flesh.)
The Bestiary entry for the Antlion: "When antlions are nesting, they hide in the surface. To defend their eggs, they projectile vomit hard globs of sand at trespassers."