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Army Ants: Facts, Types & Life Cycle

Instructor: Sarah Phenix
In this lesson, you will explore the warring world of the army ant. We'll discuss where they are found, what makes these ants different than other ants, and how their life cycle results in sedentary, roaming and active phases of their life.

Army Ants: A Name That Doesn't Lie

Soldier, Army Ant
Army Ant Soldier

Most ants are merely a nuisance; they crawl on you outside or they try to sneak a chip at your picnic. All in all though, they seem pretty harmless. You may even have fond childhood memories singing, 'The ants go marching two by two', but, don't let these particular ants fool you- they're no joke. Army ants are more like pillaging hordes of invading barbarians rather than the sweet creatures you saw in Pixar's A Bugs Life.

The classification 'army ant' is actually a general term that refers to any of about 18 genera (plural of genus) of ant that exhibit extremely aggressive nomadic behaviors and indiscriminately kill by overwhelming prey with their massive numbers. They're also known as 'driving ants', 'legionary ants', or 'visiting ants' because they 'visit' but don't stay; they pass through an area like a swarm of locusts and wipe out anything in their path.

Distribution

There are about 12 thousand identified species of ant, but only about 200 are considered 'army ants'. While ants are ubiquitous, army ants only exist in hot and humid environments. They're commonly found in the southern U.S., Central and Southern America, as well as Africa and Asia, however, not all army ants are created equal. U.S. army ants, while being equally successful search and destroy drones as their African and Asian cousins, are not nearly as aggressive. In the U.S., if your house was in their path you wouldn't have to worry about your chickens or small livestock, but some African and Asian species have been known to 'take no prisoners' and dismember livestock.

Anatomy

Typical Ant versus Army Ant
Ant Comaprison

Army ants differ from 'typical' ants in that they have much more developed mandibles. These massive jaws aren't for chewing though; they're for battle, as well as dismemberment of prey for easy transport back to the nest. What's disturbing is that, as these army ants attack their prey, they secrete an enzyme that breaks down the tissue for easier quartering but, all of this happens while the prey is still alive!

Interestingly, army ants are totally blind; they can only sense light intensity, but not discern anything in front of them. Because of this, they rely on a form of chemical communication called pheromones, which they taste and/or smell with their antennae. Ants use about 10-20 different pheromone cues to communicate with their colony as well as discern friend from foe. Some beetles, wasps, and millipedes are actually able to produce a chemical that mimics the army ant pheromone scent. This way they can actually cloak themselves from army ant 'radar' and avoid being eaten.

All Hail the Queen: Social Castes & Hierarchy

A Soldier Ant and Worker Ants
Soldier and worker army ants

Within army ant society there are three main castes, or social roles: soldiers, workers, and the queen.

Soldier ants are the largest of the nest. They have an oversized head and gigantic mandibles for defending and killing. Their mandibles are actually so large that soldier ants can't feed without assistance from the smaller worker ants.

Worker ants are smaller in size and have smaller mandibles, but they are certainly no less aggressive. They are responsible for everything from fighting on the front lines, to carting food back to the nest, and caring for the queen and her eggs. Workers tend to live about a year, which, for a soldier ant, might equal more than a few of their lifetimes.

On the other hand, the queen is protected and cared for by her colony; she is what unites the nest and so her survival is paramount. She can live anywhere from 10-20 years and tends to be the largest of the ants, with an oversized abdomen for accomplishing her reproductive needs. She is, in fact, the only reproductive female of the group. This means that the entire colony (some 300,000- 20 million ants) are most likely all her offspring. What's more is that the entire colony is female. Male ants get the 'short end of the stick' in that they are bred for reproductive needs only and then die about 48 hours after mating- that's some tough luck boys!

Barbarian Hordes: Colony Structure & Dynamic

Most ant species are solitary hunters and gatherers. They strike out on their own and, when food is found, they release a 'dinner bell'-like pheromone to which the nest responds. This is why that one lonely ant at your picnic seems to multiply into a hundred in no time flat. Army ants aren't nearly as covert about gathering food though.

Army ant hunting groups, called swarm raids or column raids, can be 200,000-20 million ants strong, fanning out into a 15-110 yard wide swath of voracious killers. These raids aren't random though- they fall into a carefully organized cycle based on the hatching and growth cycle of the young.

Army Ant Bivouac
Bivouac

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