Science

The tricks of thieving ants

The ant thieves, marked in golden, being immobilized by victim colony members, marked in green.

The ant thieves, marked in golden, being immobilized by victim colony members, marked in green.   | Photo Credit: Special Arrangement

Ants steal ant pupae from other colonies to enslave the young ones for work

To be a successful ant-thief, be faster, avoid getting caught and steal unguarded items

It turns out that successful human and ant-thieves have something in common: thieving ants — which often steal the pupae of nearby ant colonies — are quicker, avoid getting caught and steal unguarded items, shows a study published on February 28 in the journal PlosOne.

Ants often steal ant pupae from other colonies to enslave the young ants that hatch out and make them do their colony’s work. Brood theft, as it is called, is thus a convenient way to increase workforce without having to invest any extra resources.

When scientists at Kolkata’s Indian Institute of Science Education and Research (IISER) noticed the behaviour in Indian queenless ants in 2016, they investigated it further.

The team collected 20 ant colonies of this species. To identify individuals across colonies, they marked adults, pupae and larvae of a colony with the same colour. In the laboratory, they placed two colonies in a single ‘arena’ within two metres of each other. Here, the team studied brood theft in 10 different instances: what situations prompted brood theft, and how do ant-thieves steal?

Brood theft did not occur in intact nests. When the scientists disturbed both nests, ants began looking for alternative nests to relocate into. At this vulnerable stage, brood theft was more common (one every 11 minutes): ants were busy searching for alternative nests and could not defend their brood.

Ant-thieves preferred to steal pupae over larvae (pupae require no more care ), helping add 28% more pupae to their own colonies. However, each colony had very few thieves: individual thieves stole multiple times. Thieving, thus, is an advantage for ant colonies.

Fighting back

The scientists noticed that victim colonies defended themselves from this onslaught by antennal boxing (two ants face each other and repeatedly touch their antennaes quickly), chasing ant-thieves and immobilising them with a bite.

So the most successful ant-thieves had three main strategies: they spent lesser time in their victims’ nests to reduce being seen, avoided being caught and stole pupae left unattended on the nest floor.

“The Indian queenless ant is a primitive species and we did not expect it to show brood theft when we observed it for the first time in our lab,” says Dr. Annagiri Sumana, faculty, IISER.

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Printable version | Jul 9, 2020 12:54:14 PM | https://www.thehindu.com/sci-tech/science/the-tricks-of-thieving-ants/article22952945.ece

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