How instant road repairs keep army ants marching

A new study has shed light on the selfless heroism and teamwork displayed by army ants, long considered to be among the most belligerent small carnivores in the animal kingdom.

New research has found that the ants, on their way back to their nest after a feeding trip, co-operate to plug potholes on bumpy rainforest floors, "selflessly" using their bodies to smoothly pave the way for their fellow ants.

The insects, which often forage in large groups, even "choose" which of them is best to fit in different-sized gaps, and co-operate over how to fill bigger holes, according to a report publlished in the academic journal Animal Behaviour.

The trait means large groups of foraging army ants (Eciton burchellii), travelling in groups of up to 200,000, can move between their prey and nest more speedily. The sometimes-perilous rainforest route passes over numerous pitfalls, such as leaves and branches littering the forest floor.

Professor Nigel Franks of Bristol University, one of the authors of the report, said: "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." Army ants are characterised by their unique nomadic behaviour and carnivorous diet. The ants are known as "swarm raiders", foraging in dense fan-shaped swarms that can span several metres across. The ants subdue prey with powerful stings, and pull off their legs and antennae using their mandibles. They take their catch home to their nest to feed their young.

During their research, the scientists inserted wooden planks drilled with a number of different sized holes into the path of a colony of army ants' foraging route in Panama.

A Bristol University biologist, Dr Scott Powell, who worked on the study with Professor Franks, said: "The ants have a very large size range within their colony, measuring from 2mm up to 1cm (0.08-0.4in)."

"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. 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."

The researcher added that at this point, the ant becomes a "living surface", staying in place for hours at a time while thousands of foragers walk back and forth across the trail.

Military discipline

* Army ants are nomadic and make temporary nests from their own bodies. The ants form walls by fastening to each other using their jaws and claws.

* Nests are hierarchically divided. The larger soldiers focus on defence, the medium-sized workers forage and the smallest tend the queen's brood.

* The ants migrate to find food, "marching" at night. Acting together, they can kill lizards, snakes, chickens, pigs, goats, scorpions and even birds.

* The ants begin life as a microscopic egg, which develops into a larva lacking eyes or legs. The larva pupates, emerging from its cocoon as an adult.