Africanized Honey Bee (Apis mellifera scutellata)
South and Central America, the American Southwest
Why you must fear it:
You know how you can spot one of these? You can't. There is no physical way to determine the difference between an Africanized bee and a common European bee. None whatsoever.
You can, however, easily tell the difference based on their behavior. Regular bees will give you about nine seconds of being too close to the hive before deciding you're a threat and then attacking you. So it's pretty easy to just walk past them without any screams. And if you do get them after you, they'll consider you to be 'chased off' after about 300 feet.
Africanized bees do not roll this way. They give you half a second of being too close before they decide it is time to completely fuck your shit up and empty the entire hive--tens, maybe hundreds of thousands of angry, angry bees. When you run, flailing and crying and soiling yourself while screaming "JESUS CHRIST I'M COVERED IN BEES," they will chase you for over half a mile.
More scary shit:
Africanized bees owe their existence to science. Warwick E. Kerr created them in Brazil during the 1950s by crossing a European bee with an African bee. He wanted a bee that could live in the jungle. He got a bee that swarms by the hundreds of millions, is insanely territorial, mindlessly aggressive, has killed anywhere from a few dozen to a few thousand people. And, can live in the jungle.
And after they escaped and swarmed northward, it turned out they were a-OK with deserts, too. They'll be in Montana by 2010.
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, 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...