Antlion Larva

You will not find one wandering. They only exist because an antlion egg broke, and an egg breaks to any weapon or tool that touches it, including a stray pickaxe swing or the far edge of a wide melee arc. One egg can release several at once, so a careless swing near a cluster becomes a crowd before your attack animation has finished.

Small, fast, able to jump, and arriving in numbers is the worst combination to meet in the first few hours of a world. They clear a one block ledge without slowing and get inside your swing, and desert tunnels rarely leave you room to back up. Pop eggs from a distance, one at a time, or mine around them and leave them where they are.

Unlike the Alien Larva, these do not mature into anything larger. Leaving one alive costs you nothing later, so if a group gets ahead of you, walking off is a real answer rather than postponing a bigger fight.