Adult male ants single out rivals when they are born... and then chemically tag them for extermination by 'death squads'

Constant patrolling of the nest ensures that a male Cardiocondyla obscurior ant is able to bite or chemically tag a rival as soon as he is born

Chemically tagged ants are then quickly destroyed by workers in 'death squads'



Adult ants are able to identify potential rivals before they emerge from their pupae, a study has revealed.

Constant patrolling of the nest ensures that a male Cardiocondyla obscurior ant is able to bite or chemically tag a rival as soon as he is born.

Chemically tagged ants are then quickly destroyed by workers in 'death squads', according to researchers from University of Regensburg and IST Austria.

An adult male Cardiocondyla obscurior ant (left) fights a newborn 'rival'. Constant patrolling of the nest ensures that the adult is able to bite or chemically tag a rival as soon as he is born

When ants emerge from their pupae - or eclosion - they are vulnerable to attack because their exoskeleton has not yet hardened to protect them and their mandibles are also too weak to bite an attacker.

And a rival is easy to spot because male Cardiocondyla obscurior ants are diphenic, either winged or wingless.



The dominant wingless male ant, therefore, keeps an eye out for newborn winged ants.

The researchers investigated the behaviour of male ergatoid C. obscurior ants in response to newly pupated males and females, as well as their interaction with developing pupae.

It would be advantageous for newly emerged males to hide from attackers.



However, while winged males use chemical female mimicry to avoid being detected, young wingless males are easily detected and attacked by older males.

If the fight occurs during the first day after eclosion the older male will always win, but once the younger male's exoskeleton hardens his chances of surviving rises to 14 per cent.

Nearly 50 per cent of fights between older and two-day old males results in the death of both combatants.

In addition to biting, the males also smeared each other with secretions from their anuses which encouraged worker aggression.

'Older ergatoid male ants are able to distinguish pupae containing females by their chemical scent from those containing males'

The older males were more likely to chemically tag two-day-olds than younger rivals - presumably recognising that they needed help to win the fight.

However, since both males end up being tagged they both suffer worker attacks.

The winners of these fights smear more and are attacked less by workers. So although this tactic overall may provide an 'edge' it is a risky strategy.

Lead researcher Dr Sylvia Cremer, from IST Austria, said: 'Older ergatoid male ants are able to distinguish pupae containing females by their chemical scent from those containing males.

'Pupae containing males are often bitten while those containing females, or winged males disguised as females, elicit a mating response.

'However, the chances of mistakenly killing a female or worker possibly prevents older males from attempting to completely destroy all rival males before they emerge from their pupae.'

C. obscurior ants produce sexual females and ergatoid males throughout the year.

In terms of colony survival this ensures that if the old dominant male dies there is a new male ready to replace him.