Army or Soldier Ant (Eciton burchellii)
The Amazon Basin. There's other subfamilies living in Asia and Africa, but these are the most notorious.
Why you must fear it:
By now, you will not be surprised to hear that these ants are, in fact, ****ing huge, with the soldiers reaching a half inch in length. You will also not be surprised to learn that they have massive, powerful, machete-like jaws half the length of the soldiers themselves. They're notorious for dismantling any living thing in their path, regardless of size. They're also completely blind, which for some reason makes the whole thing worse.
They're called 'Army' ants because their entire colony, comprising up to and over one million insects, is a 100 percent mobile battalion. They don't make permanent hives like other ants, no, they bivouac down in single locations just long enough for the queen to shit out thousands of eggs, while the soldiers spread out in wide fans daily in search of food ("food" here, means "anything moving"). Then the eggs hatch and they enter the dreaded swarm phase of their existence.
Much like the word "killer," nature takes words like "dreaded" and "swarm" very, very seriously. They carefully pick up their larvae and go on the move, a near-solid mass of insect death and horror moving steadily and swiftly along the jungle floor, flaying alive and disassembling every living thing too stupid, slow or asleep to get the living **** out of the way. There is no talk of painful stingers or ballistic acid here, no, this is terror of a far more primordial nature--the kind that simply flows over you by the hundreds of thousands and rips you apart with massive, unbelievably powerful jaws, utterly and literally blind to size and species, considering everything in their path to be a threat to the continuation of their colony.
There are reports of animals the size of horses being overwhelmed and shredded by them. Go stand next to a horse and then think about what that means for you.
More scary shit:
Army Ants are masters of wholly-organic, living architecture. For the good of the colony, the ants will use their own living bodies to build any conceivable structure necessary, latching on to each other foot-to-foot to create protective walls and ceilings against the ravages of the weather, bridges to cross otherwise impassable spans, whatever happens to be needed. (Can they form themselves into a crude catapult mechanism and launch themselves at prey? Not yet.)
There is no other living thing in the entire world that does this.
And, they're blind !