How weaver ants defend colonies from burglars!

Last Updated: Tuesday, March 13, 2012 - 10:04

Melbourne: Adept at sniffing out rivals from outside their clans, weaver ants exhibit highly coordinated responses to intruders and defend their colonies aggressively from enemies, a study on their behaviour has said.

The study that was published online in a journal Naturewissenshaften looked at tropical weaver ants Oecophylla Smaragdina, which are social insects known for stitching
leaves together to form nests.

Weaver ants are found in northern Australia, India, Africa and South East Asia.

The study revealed that the ants shared memory to sniff out rivals, similar to sports fans recognising each other by their team colours and also found that like small town
rivalries, they`re more aggressive to their near neighbours than to visitors from afar.

"The biology of social insects is dominated by genetic interests," the study co-author Mark Elgar from the Melbourne University was quoted saying in an ABC report.

"Arboreal weaver ants are polydomous, with several leaf nests making up a single colony of up to a million closely-related members," Elgar says.

"They exhibit highly coordinated responses to intruders, defending their colonies from enemies that include other ants from the same species.

"Workers that leave the nest to forage are far more likely to encounter rivals from other colonies, but we wanted to know how a worker that typically remains inside the nest tending the brood discerns whether an ant it has never seen before is a member of its own colony or a rival that should be met with aggression," he said.

Previous work had shown other species of ants respond to the aroma of unknown ants, rather than their appearance. It had also been thought that nearby nests were more
likely to be closely related and to share a chemical signature, making them less prone to attack, but the opposite turned out to be the case.

"We found that once an ant encounters a rival it somehow passes on information about that rival`s colony signature aroma and its aggression," says Elgar.

"Ants also responded more aggressively to rivals from colonies with a history of repeated incursions". These tended to come from their nearest neighbours and competitors for resources.

The researchers took ants from 12 colonies and challenged them with intruders from other colonies that were either familiar or unfamiliar based on previous encounters in a bid to study their reactions to non-nestmates.

They then recorded the behaviour of the colony which ranged from grooming and transferring food, to recoiling and mandible flaring, gaster (abdomen) flexing and nipping, and biting and grappling with the intruders.

All ants responded equally aggressively to rivals irrespective of whether they had encountered them first-hand, with the colony remaining on high alert for at least six days
after the last exposure.

"It`s a bit like word spreading about a team of rowdy football fans all sporting their team colours; the message spreads rapidly so that even people who may not have witnessed
their bad behaviour first-hand know to watch out for them.

"This raises the question of how the information is being passed on.

"In some cases, dead rivals were returned to the focal colony, presumably to give nestmates a `taste` of the rival colony`s signature odour," Elgar says.

This didn`t always happen, however, and further research is planned to identify other chemical and behavioural cues that ants use to broadcast the message.

"Their collective memory gives them a competitive edge because all nestmates are primed with information about potential threats long before they meet them.

"Weaver ants are found in northern Australia, South East Asia, India and Africa. Also known as green ants, green tree ants and orange gasters, they can be red or green.

PTI



First Published: Tuesday, March 13, 2012 - 10:04

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