Ants use Sun, memories to guide their backwards walk home

Insects - which walk backwards when carrying heavy loads of food - use the Sun's position and visual memories of surroundings to guide them home, according to a new study which shows that ants' navigational skills are more sophisticated than previously thought.
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.
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, scientists 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.

This allows the insects to maintain their course regardless of which way they are facing, researchers said.
The findings suggest ants can understand spatial relations in the external world, not just relative to themselves.

Scientists, including those from the University of Edinburgh in the UK, studied a colony of desert ants 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.

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.
Researchers observed that ants set off in the wrong direction when a mirror was used to alter their perception of the Sun's location.
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.

"Ants have a relatively tiny brain, less than the size of a pinhead. Yet they can navigate successfully under many difficult conditions, including going backward," said Barbara Webb from the University of Edinburgh.
"Understanding their behaviour gives us new insights into brain function, and has inspired us to build robot systems that mimic their functions," she said.
The study was published in the journal Current Biology.