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How ants walk backwards carrying a heavy load and still find home

Myrmecia croslandi ant carrying its prey backwards. Flickr/Ajay Narendra, Author provided

How ants walk backwards carrying a heavy load and still find home

Myrmecia croslandi ant carrying its prey backwards. Flickr/Ajay Narendra, Author provided

Imagine carrying something heavy, like a couch, and walking backwards as you move it to a desired place. Now imagine doing it alone every day for tens of kilometres, but with the same ease as walking forwards and still reaching the place.

This is similar to what the Jack Jumper ant, Myrmecia croslandi, does almost everyday.

But the ability of these ants to navigate and reach home is not diminished by walking backwards while dragging heavy food, according to a study by researchers at the Insect Robotics Lab at the University of Edinburgh, Scotland, published in Frontiers of Behavioural Neuroscience in April this year.

How these ants do this is an interesting problem, and figuring that out could have a use in some of the latest technologies on driverless cars currently under development. More on that later.

The hunt for food

Myrmecia croslandi are commonly found in the eastern regions of Australia and nest in the ground. They get the name Jack Jumpers due to their ability to jump.

Each morning, individual ants go out searching for food (nectar or insects), and if they find an insect, they sting it and pick it up in their mandibles (insect jaw).

If the food is heavy, the ants drag it backwards while occasionally looking forward, and still manage to make their way home.

You may have seen ants in your garden carrying a dead insect or some other source of food. Some ants work together to carry the food.

Others pull it alone.

Whether they do it together or alone, they all need to reach home once they have found food. But how do they know their way back?

Finding their way home

You might know that some ants use chemical trails to navigate from one place to another.

But solitary foraging ants such as the Jack Jumpers do not use the chemical trails. So how do they not get lost?

A Jack jumper species pulls its prey backwards.

The solitary foraging ants use various visual cues to navigate: the sun’s position, panoramic view, landmarks and so on.

A widespread assumption is that an ant scans and memorises all the nest-ward views while it goes out foraging – similar to taking snapshots.

When it has to return home, it matches the memory of experienced views to current views and moves towards the direction with minimum difference between them (retinotopic alignment), while comparing the views continually.

Researchers at the Insect Robotics Lab tested this by displacing ants from their nest and seeing if they could return while pulling food backwards. That is, without facing the same way as when their memory was stored.

Surprisingly, the ants took similar paths home as they would moving forwards without food. This means that continuously aligning themselves towards minimum difference in the view comparison might not be necessary.

So how do they navigate?

Barbara Webb was the principal investigator of the study and, in an email conversation, she said the ants could be taking images and comparing them continuously, but are able to mentally rotate the views to adjust to backward walking.

Alternatively, they could be matching the views only when they occasionally look forward, and then make corrections to their path accordingly.

In this case, they could be maintaining their chosen direction by using a sky compass, such as the sun or other cues. This means they use information from visual memory and also the celestial cues from the sky to travel in the right direction.

Driverless cars

Self-driving cars or autonomous robots could have something to learn from the humble ants, and the race is on to find the best way for them to cope with a range of conditions, including severe weather.

What if self-driving cars were constantly taking images of their surroundings to monitor traffic lights, road signs, pedestrians etc. In addition to other ways of sensing the surroundings, they could use the same set of simple rules that ants use to visually navigate in their complex terrain.

Further studies are obviously needed to try to answer how these ants manage to navigate. Until then, you know what to do next time when you see ants in your kitchen or garden. Give them a cookie crumb and observe them lug the heavy booty. Perhaps displace them with the crumb to a far place, and see what they do.

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