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Last Updated: Saturday, 26 May 2007, 22:59 GMT 23:59 UK
'Living plugs' smooth ant journey
Army ant plugging hole (Scott Powell, University of Bristol)
The ants plug gaps to smooth the trail
A scientific study of the teamwork of army ants has discovered how they are prepared to let their fellow ants walk all over them to get the job done.

Scientists from the University of Bristol observed that, when ants were foraging on rough terrain, some of them used their own bodies to plug potholes.

They even chose which of them was the best fit to lie across each hole.

The technique provided the rest of the group, which can number 200,000, with a faster route between prey and nest.

The research, published in the journal of Animal Behaviour, said that the team first noticed the army ants' (Eciton burchellii) unusual behaviour in the insects' native rainforest home in Panama.

I think every road user who has ever inwardly cursed as their vehicle bounced across a pothole... will identify with this story.
Professor Nigel Franks

To investigate this further, the researchers inserted wooden planks, drilled with a variety of different sized holes, into the army ants' trails.

They found that the ants did indeed plug the holes, but the team also discovered that individuals would size-match themselves to a hole for the best fit.

Wobbling about

"The ants have a very large size range within their colony, measuring from 2mm up to 1cm (0.08-0.4in)," explained Dr Scott Powell, a biologist at the University of Bristol and an author of the paper.

"When the ants bump into a hole they cannot cross, they edge their way around it and then spread their legs and wobble back and forth to check their fit.

Army ant plugging hole (Scott Powell, University of Bristol)
As the traffic diminishes, the ant pops out and heads home

"If they are too big, then they carry on and another ant will come along and measure itself in the same way. This carries on until an appropriately sized ant plugs the hole."

At this point, Dr Powell told the BBC News website, the ant becomes a "living surface" remaining in place for hours at a time while thousands of foragers walk back and forth across the trail.

"At the end of the day, when the traffic eventually diminishes, the ant that forms this motionless plug will detect that and pop out of the hole and run home," Dr Powell said.

The scientists found ant-plugged smoother surfaces speeded up the route from prey to nest and also increased the daily prey intake, which for army ants consists of other species of ants and other bugs.

Dr Powell said: "Broadly, our research demonstrates that a simple but highly specialised behaviour performed by a minority of ant workers can improve the performance of the majority, resulting in a clear benefit for the society as a whole."

Co-author Professor Nigel Franks, also from the University of Bristol, added: "I think every road user who has ever inwardly cursed as their vehicle bounced across a pothole - jarring every bone in their body - will identify with this story.

"When it comes to rapid road repairs, the ants have their own do-it-yourself highways agency."

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