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Sun and memories help ants navigate backwards

Desert ants rank among the best insect navigators in the world, and now a scientific study shows their navigational skills are even more sophisticated than previously thought.

Scientists have revealed how the insects – which walk backwards when carrying heavy loads of food – use the sun’s position and visual memories of their surroundings to guide them home.

Ants were known to use both processes but, until now, these were assumed to be two separate reflexes that required ants to be facing in their direction of travel. Instead, researchers have shown that ants walking backwards will occasionally look behind them to check their surroundings, and use this information to set a course relative to the sun’s position. In this way, the insects can maintain their course towards the nest regardless of which way they are facing, the team found.

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The findings suggest ants can understand spatial relations in the external world, not just relative to themselves.

The surprisingly flexible and robust navigational behaviour displayed by ants could inspire the development of novel computer algorithms – step-by-step sets of operations – to guide robots.

An international team of scientists, including researchers at the University of Lincoln and the University of Edinburgh, studied a colony of desert ants in Seville to see how the insects navigate when transporting different-sized pieces of food. Although they usually walk forward when carrying small pieces of food, ants often walk backwards to drag larger items to their nest.

The team sunk barriers into the ground to create a one-way route to the nest. They then gave ants either a small or large piece of cookie, and observed how they made their way home.

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Dr Michael Mangan, based in the School of Computer Science at the University of Lincoln, specialises in modelling the navigational behaviour of insects and explores how this can translate into cutting-edge robotics. Dr Mangan said: “These amazing animals navigate through complex habitats despite their tiny brains and poor quality eyes.  Here we show how a simple “peeking” behaviour allows homing ants to combine directional information from multiple. Revealing their navigational strategies could lead to development of new sensors and control systems for robots.”

Previous research has shown that ants walking forwards find their way by comparing what they see in front of them with visual memories of the route. The team found that ants traveling backwards instead use the sun’s position in the sky to guide them.

To ensure they stay on course, backward-walking ants also routinely drop what they are carrying and turn around. They do this to compare what they see with their visual memories of the route, and correct their direction of travel if they have wandered off course.

Future studies could help to determine the interplay between different regions in the ant brain that enables the insects to use and combine different forms of navigation, the team says.

The study, published in the journal Current Biology, was funded by the Engineering and Physical Sciences Research Council. The research was carried out in collaboration with other scientists at the Australian National University and the French National Center for Scientific Research (CNRS).

The study has been covered by media outlets around the world, including BBC News Online.

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