Fire Ant – Solenopsis invicta
Dr Charlotte Sleigh has studied how we viewed ants throughout history. In this article we focus on the Fire Ant or Solenopsis invicta
Dr Charlotte Sleigh
Charlotte Sleigh “I think the 18th century is a period when you start seeing some really sustained interest in ants and the way that they live, and a lot of those very earliest writers were coming from a theological tradition. Indeed, many of them were ordained clergymen. The qualities that the ants exhibited were considered to be really twofold. One of them was industriousness, they worked, really, really hard, and that’s something everybody should do, and the other thing that the exhibited was what the Victorians called mutual aid. That is to say, they helped one another, and supported one another in the life of the nest.”
And as the Victorians travelled the world on the business of Empire, they encountered new and intriguing species of ant. One such traveller, an English engineer called Thomas Belt, particularly admired the leafcutters.
Charlotte Sleigh “Thomas Belt was a mining engineer, and when he went out to Nicaragua, around about 1870, he was not impressed with the native Nicaraguans, he was not impressed with the Hispanic colonists, he thought they had become sort of lazy and dependent on the native labour, but what he really rated where the leafcutter ants, and in particular, he was so tremendously impressed with the mining that they did, just like he was planning to, with the tunnels they constructed, it was as though he had found the English in Nicaragua in the ants.”
Watching our leafcutters at work, it’s easy to see why Thomas Belt was so impressed. Their leaf cutting operation is a highly-sophisticated, highly-organised collective endeavour. This remarkable ability to cooperate isn’t unique to the leafcutters.
Adam’s been investigating one other species of ant that takes the idea of cooperation to a whole new level, and resumes the commentary.
Floating on the Amazon River is a wonder of the animal world. It may look like a tangle of weeds, but up close, it’s a seething mass of ants. This is Solenopsis invicta, the fire ant. To survive the regular floods of the Amazon, an entire ant colony can join together as one large raft, built from their own bodies.
They can survive like this for months, waiting for dry land. So, how do the fire ants do it?
I’ve come to Georgia Institute of technology in America, to meet a scientist who’s tried to discover the secrets of the fire ant raft.
It’s my first chance to see these extraordinary boat-builders up close.
Nathan Mlot
Nathan Mlot “One of the big questions people ask is what happens to the ants on the bottom. Do they drown, and the answer is no. They essentially remain dry, even those ants that break through the surface tension of the water and are fully submerged trap a layer of air around their bodies so they can still breathe.”
So there is an obvious thing for us to do now, which is to try and submerge them and see what happens. Can you push these down?
Nathan Mlot “When you push it under the water, they retain a pocket of air around their bodies. It’s almost encapsulating them inside an air pocket. I can show you that here.”
They’re very buoyant. So there’s a silvery sheen over the outside, which is all the air bubbles that have been trapped.
Nathan Mlot “That’s the air-water interface line, there.”
Each fire ant is naturally water repellent. Droplets simply slide off them. And when thousands of ants combine, the result is a raft that is virtually unsinkable.
Nathan Mlot “When you do push them under the water, they pull themselves even tighter together, so that when they’re subjected to the high pressures underneath the water, it still keeps the water out.”
Magnified hundreds of times, the secrets of the fire ant raft are revealed. The mandibles are used to grab hold of a nest-mate’s leg. At the end of each leg is an adhesive pad and a claw. This, like a sticky grappling hook, allows them to form further flexible connections with any nearby nest-mate. The ants’ own bodies act as a set of interlocking units, so the entire colony can turn itself into a single structure.
So this is really an unsinkable, self-healing lifeboat?
Nathan Mlot “It is. It is a force to be reckoned with, that’s for sure.”
This remarkable ability allows the fire ant to survive the worst floods of the Amazon. Cooperation has made them an engineering marvel of the natural world. And one of the most successful ant species on the planet.
External Links
Fire Ant – Wikipedia Page
