Forget lions, tigers, and bears. Forget even our own famously aggressive species. When it comes to the art of war, it's army ants that will make you break into a cold sweat. Armored tough, with machete jaws, these masterful ﬁghters hack and dice prey vastly larger than themselves by acting in numbers beyond easy comprehension. Imagine hordes of spear-wielding humans at a wooly mammoth's feet. That’s the scale of army ant operations when they're attacking a tarantula or scorpion. Army ant colonies succeed at making tens of thousands such kills each day. Folklore to the contrary, their prowess does have limits. Their dragnets don't take down livestock or people (though some African species occasionally live up to that image).
I went to one of the best places to observe army ants in action, Barro Colorado, a six-square-mile island in a lake created by the Panama Canal and home to perhaps 50 colonies of Eciton burchellii, the most studied army ant in the world.
The ways of E. burchellii helped give rise to the name army ant. Their colonies are huge, ranging from 300,000 to 700,000. They are mobile, moving from nest site to nest site. Though not all army ant species share these characteristics, there's one hallmark they have in common: a shock-and-awe hunting strategy. Other ants search for food individually, sometimes using scouts. Army ants set out en masse. Being blind, they can't see what's ahead of them, but moving in such numbers they easily overwhelm their prey. For E. burchellii that's usually non-army ants and large arthropods. They can also kill, but don't eat, lizards, snakes, and frogs that fail to get out of the way. Their attack formation is called a swarm raid. As many as 200,000 ants leave the nest in a swarm that broadens into a fan as wide as 15 yards. Specialized birds follow the raiders, picking off prey as it scatters in vain attempt to survive.