Ants go marching

• Just like humans, ants also enslave, build colonies and rebel

NOV 17 -

The animal world fascinates me for two reasons. Their talents and abilities far exceed ours. And, they are so similar to humans in the way they experience emotions and handle problems. And no species are more humanlike than ants.

None of us like working. We would all like to be waited on hand and foot. Many nations go to war for slaves—the Roman Empire was built on them. The Americans picked them up from Africa. The entire middle-class upwards of India exists because someone else, who needs the money, comes in to cook, clean and look after their children.

Temporary parasites

Some species of ants feel the same way. They parasitise other ants using aggression and deception. In fact, entomologists go out into the fields looking for the ultimate thrill: encountering a raiding party of slave-making ants. There are three main types of ant parasites: temporary social parasites, ants that live in the nest of the other species and slavemakers.

Temporary social parasites depend on other ant species only during the establishment of new colonies. As soon as the young queen finishes her mating flight and is inseminated, she penetrates a host colony, kills the original queen, and gains acceptance of the workers. The parasitic queen then lays eggs that develop, with the care of the host colony workers, into a worker force. Eventually, the host workers die leaving only the parasitic queen and its offspring. So a mature colony contains only members of the parasitic species.

Since the main defence of every ant colony is a recognition system based on smell, some invading queens fight with workers of the host species outside the nest, kill them, take their odour sacs and obtain a chemical disguise before entering the host nest.

The slavemakers, Chalep-oxenus and Harpagoxenus, kill all the adult workers. New workers come from the conquered brood and they rear the brood of the parasite.

While temporary social parasites typically kill the host queens, in some species, the queens and ants that settle down permanently in the nest of the other species are usually tolerant of the host queens. They are bigger.

Other variations on these hostile takeovers include one South American species whose workers secrete a chemical that causes the ants of the host colony to evacuate the nest. In their haste to leave, the babies are left behind. These are then taken back to the raiders’ nest.

Making slaves

The slavemakers are the most human like. These raid other ant colonies to steal the babies. Some of the stolen larvae and pupae are eaten. The others are turned into worker slaves that are chemically imprinted and completely integrated into the society of their enslavers. The slaves tend the nurseries, gather food, feed their enslavers, care for the queen, and defend the nest against threats. If the colony moves to a new location, the slaves physically carry their enslavers to their new nest. Sometimes, the slaves even help slave-making workers in raids against other ant colonies of their own or closely related species. In fact, in some species, the workers are strictly bred for the purpose of going out and conquering other nests.

Slavemakers differ. Some, like Formica subnuda, fight for hours and mortality is high in both invader and invaded workers. So they raid small new colonies and keep slaves only upto 10 percent of their workforce.

In sharp contrast, P. breviceps with their enlarged glands and sharp sickle-shaped mandibles have slaves that comprise 90 percent of the work force. How are their raids so successful? Magic! They emit a secretion which pacifies or turns workers from the raided colony against each other. Workers that are immune to the magic and offer resistance are immobilised by piercing their heads with mandibles.

The queens of slavemaker ants such as Protomognathus americanus produce a special kind of offspring .These are not normal workers but scouts, whose only job is to identify ‘host’ ant colonies suitable for attack. A small slavemaker colony may consist of one queen, two to five workers and 30 to 60 slaves. Scout ants are very valuable because their decision about suitable raid targets has to be right or the raiders get wiped out. During the attack, slavemaker ants steal host pupae and take them back to their own colony. The pupae are imprinted by the odour of the slavemaker colony and grow up to perform all of the ordinary worker tasks.

Slavemakers don’t go charging in at random. In fact, they target the strong over the weak when seeking new servants. Larger, better defended colonies are chosen over smaller, weaker ones because the ants have reasoned out, those strong defences mean strong workers who would do more work. In fact, slavemakers and their victims are usually closely related.

Fight the power

But slave keeping, as the Romans learnt, has its own drawbacks. The slavemakers are lost without their slaves—they cannot nurse, forage for food or manage any colony task. This ant must have slaves to survive, and mature colonies must obtain a minimum of about 6,000 slaves per season per colony.

Do the slaves live their lives hopelessly or do they ever rebel? Ants wouldn’t be similar to humans if they didn’t. Temnothorax longispinosis enslaved by the dark, bulbous-headed ant called Protomognathus americanus, tasked with feeding and caring for their slothful masters and their children, will, every now and then, lead a major rebellion. The slaves will just stop feeding and cleaning the young ants in their care, leading them to die. Sometimes, a group of slaves will incite an all-out revolt and dismember the young in a gruesome game of tug-of-war, killing upto 70 percent of them. Like Spartacus, they may not be able to save themselves but this mutiny can reduce the number of slave-masters and save other colonies populated by the slaves’ relatives.

Do you think God ran out of ideas and simply made a miniature version of the human species?