The term 'army ant' is a general term which refers to any of about 18 genera of ant that exhibit extremely aggressive nomadic behaviours. Army ants are known to indiscriminately kill by overwhelming prey with their massive numbers. Army ants do differ from the typical ant and contain a much more developed mandible which are used in battle to easily dismember their prey and carry back to the colonies.
These ants are great in battle, but interestingly army ants are completely blind. By only sensing light intensity, these ants rely on a form of chemical communication called pheromones, which they taste and/or smell with their antennae. There are about 10 to 20 different pheromone cues which they use to communicate with their colony as well as discern friend from foe.
Army ants are also commonly known as visiting ants as they do not make a permanent nest for their colonies but rather create temporary nests called bivouacs. The Bivouacs house and protect the colony during their sedentary stage where the queen lays between 30 000 and 300 000 eggs. Bivouacs are made of living worker ants that have hooked together their legs and mandibles. Some species create these living nests underground while others stay above. After the eggs have hatched the colony is signals and moves along to a new location.
When army ants hunt they form swarm raids or column raids which can include 200,000 and 20 million ants. An interesting video has circled the internet showing the impressive skills of army ants and just the extent they will go to.
Thousands of army ants in Costa Rica miraculously worked together to build an impressive rope bridge, using their own bodies to swarm in a high-altitude wasp nest. "Attack of legionary ants, also known as army ants or marabunta, to a wasp honeycomb. It’s impressive the level of swarm intelligence and collective computation they use to form that bridge."