How ants enlist emergency help

27 June 2012 Last updated at 09:20 By Victoria Gill Science reporter, BBC Nature

See the ants' "chemical nets" dragging nestmates towards the food item

Brazilian "big-headed" ants use chemical trails to drag others into helping them carry food, a study shows.

Researchers found that when an ant discovered food that was too large to carry, it immediately set off for the nest, laying a pungent chemical trail.

This almost instantly caused hundreds of other ants to rush in and help drag back the oversized snack.

The team thinks the species' "chemical breadcrumb trail" is the fastest and most accurate ever recorded.

The findings from this study are reported in the journal Behavioural Ecology and Sociobiology.

To me, to you

Only ants and humans are able to "organise themselves into teams" to lift heavy objects.

Although many ant species use chemical trails to organise themselves into food-collecting groups, the big-headed ant has an "extreme" chemical enlisting strategy, says the University of Sussex team.

Tomer Czaczkes, the scientist who led the study - and who filmed the ants at work in the forests of Brazil - said that the insects were "incredibly accurate" when it came to following the trail laid down by a fellow forager.

"When an ant finds something delicious," he said, "she has to lay a trail really quickly, because competition is fierce.

"The pheromone trail starts working immediately. Any ants caught in its net are funnelled towards the food item."

In their experiments, Dr Czaczkes and his colleagues left food items outside an ants' nest and filmed the reaction.

When one "scout ant" found the food, it would try to move it, give up and return to the nest, laying the pheromone trail on its way back.

Within two seconds, other ants would emerge from the nest and start following the scent to the food item.

This strong-smelling trail decays quickly, lasting just six minutes. This is a crucial part of its purpose, as it does not lure ants from the nest pointlessly, after a food has gone.

"That's important, because for an ant, it's dangerous to be out of the nest," said Dr Czaczkes.

But because the trail also intercepted ants that were already outside the nest - dragging them towards the food item, the tiny, industrious insects were able to retrieve food up to 8m from their nest.

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