3:28 pm - Tuesday November 3, 2015

Some species of ants using aggression and deception

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Some species of ants using aggression and deception
Some species of ants using aggression and deception

The animal world fascinates me for two reasons. Their talents and abilities far exceed ours. They are so similar to humans in the way they feel emotion 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 the children.

Some species of ants feel the same way. They parasitize other ants using aggression and deception. In fact, entomologists go out into the field 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 slave-makers.

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 by the workers. The parasitic queen then lays eggs that develop, with the care of the host colony workers, into a worker force of their own offspring. Eventually the host workers die leaving only the parasitic queens and their offspring. So a mature colony contains only members of the parasitic species. For instance, the queen of the Myrmoxenus ravouxi species will fake death to entice ants from another colony to drag her back to their nest, where she awakens and kills the nest’s original queen. She will then cover herself in the dead queen’s pheromones, and will begin producing eggs. Her children will overrun the colony.

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 slave makers Chalepoxenus 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. For instance the Swiss ant Teleutomyrmex schneideri have concave abdomens and long tarsal claws which enable them to grip onto the host queens and ride their backs. Despite the burden, the host queens continue to produce worker offspring and so the mixed species colony is permanent. The host workers simultaneously rear the brood of both the parasitic and non-parasitic queens.

Other variations on these hostile takeovers include one South American species whose workers secrete a chemical on a host colony 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.

The slave-makers 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 participate with the 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 as only about 10% of their workforce.
In sharp contrast, slave-makers like P. breviceps with their enlarged glands and sharp sickle-shaped mandibles have slaves that comprise 90% 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 immobilized by piercing their heads with the 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 the slavemaker ants steal host pupae and take them back to their own colony. The pupae are imprinted on 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 that strong defences means strong workers who would do more work. In fact the slavemakers and their victims are usually closely related.

But slave making, as the Romans learnt, has its own drawbacks. The slave makers are lost without their slaves – they cannot nurse, forage for food or manage any colony task. In fact P. breviceps cannot survive on its own even if plenty of food is available. This ant must have slaves to survive, and mature colonies must obtain a minimum of about 6000 slaves per season per colony.

A typical colony of 3,000 slave-making ants may have more than 6,000 slaves working for it.

Do the slaves live their lives hopelessly or do they ever rebel? Ants wouldn’t be human if they didn’t  Temnothorax longispinosis ants enslaved by the dark, bulbous-headed ant called Protomognathus americanus, tasked with the feeding and care of 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%. 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?

Maneka Sanjay Gandhi

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