A fun piece on ants and instrumental convergence:

Each month millions of Argentine ants die along battlefronts that extend for miles around San Diego, where clashes occur with three other colonies in wars that may have been going on since the species arrived in the state a century ago.

Some notes on ant warfare

Many are aware that a world war between Argentine ant supercolonies is currently underway, across multiple continents, and against multiple ant 'nations'.

Ant conflict differs from species to species and from scenario to scenario. Some use sheer numbers in tight phalanx-like organisations to swamp the enemy, which may include ants many times their individual size.

The species of the aggressor matters - when researchers placed a single dead slave-making ant into a slave-host colony for 5 mins, the response was extreme aggression against almost all neighbours for three days, most especially against slave-taking ants.

Treating known neighbours or strangers with more hostility is a strategic choice that ant colonies must make, and these choices often determine how aggressive a colony will be.

Ants that cannot afford huge losses with each battle might opt for ranged weapons such as chemical attacks or dropping stones onto the enemy's heads and nest entrances.

Slave making ants are usually outnumbered when they raid other nests. In order to successfully capture the brood to raise in their own nest they must pacify the defenders, which is often done using pheromones to sow confusion and discord amongst the ranks.

!!!!!!

Certain mathematical models derived from human conflicts can explain the success of swamping the enemy with large numbers of disposable soldiers.

That said, some species prefer stronger individuals, and may even use personal champion style duels whilst fighting. Leaving the battlefield for the night and returning in the daylight has also been documented during large scale conflicts.

I may add some more notes as I read. Some of the papers go into marvellous detail on the tactics and change in fighting styles over many days of warfare.

I hadn't heard about ant slavery, apparently it's a well-studied phenomena.

From the Wikipedia page:

The slave-making ants are specialized to parasitize a single species or a group of related species, and they are often close relatives to their hosts, which is typical for social parasites. 

The slave-makers may either be permanent social parasites (thus depending on enslaved ants throughout their whole lives) or facultative slave-makers. The behavior is unusual among ants but has evolved several times independently.

Theft of brood for the purpose of employing the stolen individual's efforts in support of the thief is called dulosis (from Greek δοῦλος, "slave"), but the term "slave-making" is used in older literature and is still common.^[1] There is some controversy associated with using the term "slave" and "slave-maker" to describe the natural history of this species. Additionally, there are species commonly raided that are referred to as "negro ant" specifically because they are common victims of ant raids, although this is not endorsed by nomenclature societies^[2] and may cause offense. Some have argued that using such non-inclusive metaphors in science is harmful to scientists and interferes with the unbiased scientific process.

A colony may capture 14,000 pupae in a single season.^[9] Most slave-raiders capture only the young, but Strongylognathus sp. also enslave adult workers.

Later, enslaved workers emerging in the parasite nest will be imprinted on and integrated into the mixed colony where they will rear the parasite brood, feed and groom the parasite workers, defend the nest against aliens (e.g. other insects or spiders), and even participate in raids,^[8] including those against their original colony.

Only one slave species is usually found in a single Polyergus nest. This is in contrast to related facultative slave-makers of the genus Formica belonging to the F. sanguinea species group, found in the same habitat, whose nests commonly contain two or more species serving as slaves. Choice of a host species can occur both through the colony-founding behavior of queens and through the choice of target nests for slave raids. The parasitic Polyergus queens found colonies either by adoption, where a queen invades the nest of a slave species, killing the resident queen and appropriating workers and brood present, or by "budding", in which a queen invades or is accepted into a host species nest accompanied by workers from her nest of origin.

The first hypothesis concerning the origins of slave-making was Darwin's (1859) suggestion in On the Origin of Species that slavery developed as a by-product of brood predation among related species. Other hypotheses focus on territorial interactions with opportunistic brood predation or brood transport among polydomous colonies (consist of multiple nests) as the main pathway to slave-making.^[20][21] Slave-making behavior is unusual among ants but has evolved independently more than ten times in total^[10] including in the subfamilies Myrmicinae and Formicinae.^[22][23] Slave-makers and their hosts are often close phylogenetic relatives,^[24] which is typical for social parasites and their respective hosts (formalized as Emery's rule). This has major evolutionary implications since it may argue for sympatric speciation.^[25]

Raids can jeopardize host colony survival, therefore exerting a strong selection pressure upon the hosts. Reciprocally, there is some evidence that hosts also exert a selection pressure on their parasites in return, since resistance by host colonies might prevent enslavement. Coevolutionary processes between slave-making ant species and their hosts then can escalate to an evolutionary arms race.^[8]