War can vary, depending on the size of the population. In smaller groups, fights can be ritualistic, as they often are in tribal human groups. Honey-pot ants — they will face each other off. They stand on their toes trying to make their enemy believe that they are much bigger. In this method, no one has to be hurt. Ants are scared away, and the ones with the most left standing there wins.
In larger groups [tens of thousands or millions], ants battle without hesitation. Marauder ants in Asia clash in broad fronts of tens of thousands, and mow each other down. A leg pops off here, antennae pop off there.
It's safer to fight at a distance, as humans have done ever since the spear was invented. Some ants have chemicals they shoot out of a gland associated with their stingers. One species even drops rocks on the heads of its competitors.
What are super-colonies? Why do ants form them?
Only a few ants and humans can build societies of any imaginable size. Some of the most dangerous species have that capacity, expanding their territories indefinitely to form super-colonies. The ants in each super-colony share a common identity, their own nationality — they are one big, unified society.
That has happened here in California with Argentine ants. They came here about a century ago. Their colonies have the ability to just keep growing in population. There is a colony here in California that stretches between San Francisco and the Mexican border and weighs more than the entire city of Carmel. It is very uninventively called the "Very Large Colony."
You can take an ant here in L.A. and drive it down to San Diego and drop it off, and it would blend in seamlessly with its nest mates there.
What species are in Los Angeles specifically?
The Very Large Colony has taken over the Los Angeles basin. Many of the species that were here originally 100 years ago are being driven to extinction by this ant. There are repercussions to that in terms of biodiversity loss, for plants and animals both.
Was it difficult to locate ants in some of the more complex terrain [thick forest, vast deserts] that you visited?
The really cool ants are hidden away, with small colonies that are hard to find. When you have a research grant it's a combination strategy: You pick out the thing you think you can find, and stealthily look for the rare gems.
You describe ants as highly social creatures that express their sociality through a division of labor. Can you describe that?
Ants have been social much longer than humans, and their division of labor varies quite a bit between species. Some ants within a colony are lazy. (Ants actually sleep; most people don't know that.) What we call "elite ants" end up doing most of the work. They can influence others to pitch in, however.
Adam Smith predicted in his book "The Wealth of Nations," written during the Industrial Revolution, that the individuals of a society could start to become dumber and dumber because each is just doing one little task over and over again. Similarly, ants that live in large, structured societies have something like assembly lines, and individuals are born capable of doing one job only, or they get good at their one task over time. The result is that a single ant cannot function away from the group. Without the help of others, it's quickly dead.
Argentine ants are "global invaders." Why is this?
They come from this single area in northern Argentina that is the breeding grounds for some of the nastiest invaders on the planet.
In human warfare, there is something called the "dear enemy phenomenon." What that means is if you have warring, there is a lot of death at first, but usually, after time, a territorial border is formed and a no-man's land is created, with less mortality.
This happens in ants, too. But in this floodplain region of Argentina, the water rises and falls. Each time the water falls, the ants must reestablish their territory from scratch, and the dear enemy phenomenon is lost. The ants start killing each other with no end.
When a ship shows up, they're on it. When the ship gets to its destination, the ants disembark and continue the relentless killing of whatever local species they contact.