Army or Soldier Ant (Eciton
burchellii)

From:
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, fucking 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 fuck 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.
Now, time for the disclaimer. If you are squeamish or have a weak
stomach or value your sanity in any way, you may want to bail out
now.
Okay, here goes...