Tuesday 15th December 1:17 pm
Ants use brains and brawn to share the load
Tuesday 15th December 2015 1:17 pm
Ever wondered how tiny little ants coordinate a raid on the cat’s bowl? Humans could learn a lot from the answer, says Dr Karl.
Back in 2011, an Israeli scientist named Ehud Fonio, watched his cat’s food marching away from the food bowl. In reality, a brigade of ants was stealing his cat’s dinner. He made a film of the ants, and showed it to his fellow scientists — and they noticed something strange. It took them four years to solve the mystery.
Ants are famous for their strength. The Allegheny mound ants from North America are among the elite — they can lift 1000 times their own weight. This is equivalent to an 80 kilogram person lifting a fully loaded Boeing 737, about 80 tonnes.
Ants are also one of the few creatures (besides humans) that cooperate to build things, and to shift loads much heavier than the individual can lift.
The big mystery has always been – in matters so complicated, how do they coordinate their actions?
The previous theory was that they used the wisdom of the crowd — which is the average opinion of a group of individuals. It turns out that the wisdom of crowds works best when the crowd is quite diverse.
But in a nest, the ants are all genetically almost identical. All they do with a load is to lift it, or pull it — they don’t do a lot of pushing. When you average out all their lifting and pulling, the load of delicious take-away cat food should stay in the one spot, and not get carried back to the ant nest. So how does it get there?
Now think about the first ant accidentally stumbling across the foody goodness of a cat’s dinner. That first ant rushes back to the nest, all the way squirting out a chemical called a pheromone. Other ants stumble across this trail of pheromone, sniff it carefully with their antennae, and head in the direction where the pheromone is stronger — towards the cat food. Very soon, there’s a trail of individual ants carrying the little bits of cat food.
But what about the big lumps of cat food?
Well, there’s a large degree of randomness about ants’ movements — they mill about. But a bunch of them will end up with their heads, and antennae, shoved up against the food. (Mind you, some of them will immediately leave — but they’ll get replaced.) Then they’ll start lifting and pulling.
At the very beginning, they’ll have a memory of where the nest is — the other end of the pheromone trail. But the ants are effectively blind — because their sensing antennae are wedged up against the food. With nobody watching and guiding, the food would soon go off course.
But remember the randomness, the ants’ erratic streak. Other ants are coming and then leaving, all the time. The total number of ants lifting and pulling the food will stay roughly the same, but they’ll be a continually changing population.
Now let’s add individual behaviour into the mix. Suppose a random ant crosses the pheromone trail — then she knows where the nest is. Further, suppose that she immediately bumps into the group moving the food. So she starts lifting and pulling in the direction of the nest. She is now a leader, or steerer. Because she is near the front end of the food, she is able to direct it towards the nest — but only for a while.
After about 10-20 seconds, she doesn’t know where the nest is, because her antennae are hard up against the food, and she can’t see where she’s going. Thanks to the highly random nature of ant movements, two things can happen.
First, she changes her position and role — and turns from a leader and steerer into a lifter and puller.
Secondly, she leaves (having lost her sense of direction) and is replaced by another ant. More often than not, this new ant will know where the nest is – and now she will help steer the load, for a while.
The ants rotate jobs, sometimes checking out the locale and being a scout, sometimes lifting, and sometimes steering. The leaders and the lifters help each other, and constantly rotate in and out of their jobs. Overall, on the big lump of cat food, about 10 per cent are leaders and 90 per cent are lifters.
Maybe we can use this knowledge to design semi-intelligent robots to work in hostile and unforgiving environments, or in disaster relief?
So the scientists found that these ants were an ever-changing mix of company yes-men and rugged individualists. If all we humans wanted out of life was some stolen cat food, perhaps these ants (and their singularly selfless dedication to the task) could be the ideal model for human society?
This blog first appeared on Dr Karl's Great Moments in Science
© 2017 Karl S. Kruszelnicki Pty Ltd