Nature’s traffic engineers have come up with many simple but effective solutions

File 20180524 90281 mi9czk.jpg?ixlib=rb 1.1
Ant colonies direct traffic flows of millions of individuals along the best routes – army ants even manage inbound and outbound lanes – but how?
Geoff Gallice/Wikimedia, CC BY

Tanya Latty, University of Sydney

This is the third article in our series, Moving the Masses, about managing the flow of crowds of individuals, be they drivers or pedestrians, shoppers or commuters, birds or ants.

As more and more people move to cities, the experience of being stuck in impenetrable gridlock becomes an increasingly common part of the human experience. But managing traffic isn’t just a human problem. From the tunnels built by termites to the enormous underground networks built by fungi, life forms have evolved incredible ways of solving the challenge of moving large numbers of individuals and resources from one place to another.

But how do natural systems – which lack engineers or in some cases even brains – build and manage their transportation networks?

Building a transport network

Perhaps the most familiar animal transport systems are the trail networks of ants. As ants walk through their environment they leave behind tiny droplets of an attractive chemical called a pheromone. Other ants are attracted to the chemical bouquet and as they follow it they add to the trail by leaving their own droplets of pheromone. Like Hansel and Gretel leaving a trail of breadcrumbs, ants use their trails to find their way back home.

The Argentine ant (Linepithema humile) builds chemical trail networks that connect their nests using the shortest possible path. Connecting points via the shortest path saves on construction costs by using less material and requiring less effort.

Argentine ant trails connect nests using an approximation of the shortest path. The grey lines are ant trails visualised by overlaying several photos of the trail system. The inset shows the actual shortest path solution.
Tanya Latty- supplied

Yet calculating the shortest path between a set of points is a very difficult task. So how do ants, which have brains smaller than a pinhead, figure out the solution?

The answer is elegant in its simplicity. Short, direct paths are faster to traverse, and so more pheromone gets deposited by the higher density of ants. As ants are more likely to follow stronger pheromone trails, shorter, more direct trails attract more ants than do long meandering trails.

Meanwhile, fewer and fewer ants travel along the long paths, as they are attracted away by the stronger, shorter path. Eventually the longer paths disappear altogether due to evaporation, leaving only the direct routes. This simple mechanism allows small-brained Argentine ants to solve a difficult problem.

Australian meat ants (Iridomyrmex purpureus) take trail-building to the next level. Meat ants diligently cut away all vegetation from their trails, creating a smooth path. Unlike Argentine ants, meat ants do not connect their nests using the shortest possible route. Instead they build a network that includes extra “redundant” links.

Meat ants clear the grass from their trails and nest.
Nathan Brown, Author provided

Connecting points with the shortest path takes less time and uses less energy, but it would also result in a fragile network; any damage to any trail would isolate one of the nests.

This is less of an issue for Argentine ants, which can rapidly repair any damage to their trail system by depositing more pheromone droplets. For meat ants, however, damage to the system takes more time to fix. So rather than building a cheap but fragile network, meat ants build networks whose structure neatly balances the competing demands of cost and robustness.

Walking in lanes

In most human road networks, traffic flows are organised by dividing traffic into lanes where all the cars travel in the same direction. The army ant (Eciton burchellii) also uses lanes – two outer ones for outbound traffic, and one inner lane for nest-bound traffic.

But how do the army ants organise this? Lanes form because ants heading to the nest often carry heavy loads and so tend not to turn away during head-on collisions. Ants leaving the nest tend to veer away from their heavily laden sisters and so end up in the outer lanes.

Again, a simple set of behavioural rules allows ants to ensure they have a fast, efficient transport system.

Pothole pluggers

Potholes are an annoying and jarring part of driving that can slow traffic to a crawl. So when workers of the army ant (Eciton burchellii) encounter uneven surfaces, they take one for the team and plug it with their living bodies. Workers even match their size to the hole that needs filling.

Teams of ants cooperate to fill larger holes. Ants will even form bridges to span larger gaps. They adjust the width, length and position of the bridge to accommodate changes in traffic.

The result of these hardworking ants is a smooth, fast-flowing transport system that works even over the bumpiest terrain.

Humongous fungus

It’s not just insects that build transport networks. Brainless organisms such as fungi and slime moulds are also master transportation designers.

Fungi build some of the biggest biological transportation systems on Earth. One giant network of honey fungus (Armillaria solidipes) spanned 9.6km. The network is made up of tiny tubules called mycelia, which distribute nutrients around the fungi’s body.

The honey fungus is connected by vast underground transportation networks, spanning many kilometres.
Armand Robichaud/Flickr, CC BY-NC

Slime moulds – which are not fungi but giant single-celled amoebas – use a network of veins to connect food sources to one another.

In a highly creative experiment, researchers used tiny bits of food to make a map of the Tokyo metro system, with the food representing stations. Amazingly, the slime mould quickly connected all the points in a pattern that closely matched the actual Tokyo metro system. It seems slime moulds and engineers use the same rules when constructing transport networks – yet the slime mould does it without the aid of computers, maps or even a brain!

Slime mould form a map of the Tokyo railway system.

Nature has found many different solutions to the universal problem of building and managing a transport system. By studying biological systems, perhaps we can pick up a few tips for improving our own systems.

The ConversationYou can find other articles in the series here.

Tanya Latty, Senior lecturer, University of Sydney

This article was originally published on The Conversation. Read the original article.


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

Ravindra Palavalli Nettimi

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.

The Conversation

Ravindra Palavalli Nettimi, PhD student in Ecological Neuroscience

This article was originally published on The Conversation. Read the original article.

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