Brood Parasitism – Slavemaking Ants and Their Captives

slavemaker polyergus
Source: Wikimedia Commons; Licensing: Attribution

The army is getting ready for battle. The scouts have returned from their mission, and they’ve marked the enemy’s base. Thousands of soldiers are preparing to face the opposing force. With sharp weapons and berserker rage, they prepare to hurl themselves into the fray. The element of surprise is on their side. This one battle may decide the fate of the entire colony. It’s a fight for survival as much as it is about conquest.

No, this is not a description from a history book. This brood parasitism. There are rare species of ants called “slavemaking ants”. However, the term has been disputed by some scholars as offensive. The way they operate is quite fascinating to some, and a little bit terrifying to others. Fantastic Pest Control leaves such judgement to you.

Slavemaker Ants: Goals and Tactics

How the Slavemaking ants attack?
Source: Wikimedia Commons; Licensing: Attribution, Share-alike

Slavemaking ants have subscribed to the dogma of social parasitism. Their entire survival and the development of their colonies depends solely on the brood of other, closely related ant species. Most slavemakers lack the capacity to take care of their own brood. That’s why the workers of those colonies serve as warriors who protect the current regime and replenish the slave population. Instead, the slaves are the ones in charge of upbringing and other colonial functions.

By going on “raids” and stealing the offspring of other ants, slavemakers bring it back to their own lair and allow it to hatch inside. The new ants treat the slavemaker colony as their own and execute functions their captors are incapable of performing. Such as anything not related to expanding the colony.

Slavemakers and related species form a host-parasite relationship. The host can have different reactions to the raiding parasites, such as fight or flight. However, the more widely adopted strategic response is flight, because hosts usually lose to the more established and specialised raiding warriors.

After the battle is over, the raiders claim their prize. Being the brood of the host species, which is also the main labour force of the parasite. Most slave-maker species cannot survive in any other way. In lab experiments, they experience a high mortality rate when slaves are removed from their environment, and they’re forced to care for their brood themselves.

Slaves aren’t completely helpless as a part of the new colony, though. They’ve been known to rebel sometimes. Killing a large portion of their captors’ offspring, thus reducing their numbers and inadvertently protecting their original colonies from following the same fate. It is not yet clear when and under what circumstances these instincts kick in.

Polyergus: the Ant of War

slavemaking ant
Source: Wikimedia Commons; Licensing: Attribution, Share-alike

Among all the different species of slavemaker ants, there are none more impressive than the Polyergus. These little masters of deception are so dependent on their slaves. They literally cannot feed themselves without having their host. However, what they lack in terms of independent survival they make up for on the battlefield.

Polyergus ants excel at capturing other colonies and expanding their domain. Their colonies often have a relatively short lifespan and are pretty rare, these compulsive conquerors know no defeat, fear no enemy, and never retreat. They are the perfect soldiers. Perhaps one of the reasons for that is they’re lead into battle by their own queen.

How the Ants Attack

When they find a new colony with enough potential workers to expand the labour force, Polyergus immediately mount an attack. The queen goes into battle as well while her workers are killing the enemy. She uses the confusion to make her way to the Formica queen. Once she’s there, a battle ensues, where a complicated chemical exchange takes place. In most cases, the Formica queen is defeated, and the Polyergus queen claims her prize – the chemical identity of her fallen foe. She adopts her pheromones, fooling the Formica ants their queen is still alive and well. The adults of the colony become her slaves without even knowing it.

In the meantime, the workers of the Polyergus colony have already defeated the defending forces and have gotten away with a large portion of the brood. The Formica pupae will hatch in the Polyergus colony and become slaves. Tending to their captors’ every whim and need. And thus the colony keeps ongoing and expanding.

Obviously, this tactic has its flaws and doesn’t always work. For one, it’s risky because the queen might be killed in action. However, this is not really an issue since Polyergus colonies contain ergatoids. These are large reproductive ants that can replace the queen should she perish. But at the end of the day, looking at the complicated relationship, the two species have developed only makes us marvel at nature’s creations.

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