Ants know their math

Last Updated 11 January 2010, 09:47 IST

What is the first thing that comes to your mind when you think of ants? Tiny creatures that make their way into your home, and invade upon the food that you eat? Well, here is another attribute of ants that you need to ponder over. Some of them might know geometry, if recent research by Duncan Jackson from the University of Sheffields published in the journal Nature, has shown.

Insects are the most abundant life forms on earth, with over a million species of them discovered to date. Among all the insect species, it is the ants that have colonised every possible habitat on earth. With only 9,000 odd species, they form only one per cent of the insect species. If compared to the 3.6 lakh species of beetles or 1.7 lakh species of butterflies, ants don’t seem to stand a chance. But it turns out that if one were to weigh all insects, ants would make up 33 per cent of the weight, which highlights the tremendous  success they have enjoyed.

The success of ants has been mainly attributed to their social structure and self-organisation. Their social structure is classified as Eusocial (truly social in Latin) in which some individuals of the colony (Queens) are the only reproducing members, with others performing tasks that enable the survival of the colony. Self-organisation means the large scale order emerging out of a group of individuals who follow some simple rules (bird flocks, for example). Due to self-organisation, trail forming ants upon discovering a food source will eventually find the shortest way to the food, but without any individual ant planning to do so. It just happens!

Pheromone deposits

Many ant species create chemical trails by depositing pheromones (a class of chemicals used by many insects) as they move through their environment. Other than chemical trails which can be thought of as ant highways, the ants also make use of other features of their environment as navigational aids. These could be visual landmarks (analogous to milestones on a highway), patterns in the sky, magnetic field of the earth and so on. While there are ant species that have more than one navigational aid, there are also species that depend completely on their chemical trail.

This can lead to a serious problem in re-orientation. Imagine driving on a straight highway without milestones, in the middle of a flat desert, on an overcast day. Suddenly, there’s an accident and your car spins wildly and ends up facing some direction. How do you make out that this is really your original direction? Many ants face a similar problem.
In ground-breaking experimental studies published in the prestigious journal Nature, Duncan Jackson, the lead author of the study explains, “The ants should move away from the nest when they are foraging, and back towards it when they are laden with food but the pheromone trail leaves no way of knowing in which direction the ants are travelling.”
If you look at the trail or the bifurcation that the ants make, they open outward in the direction of food. So the appearance of the trail or the bifurcation itself should tell you the direction of the food or the nest. By means of ingenious experiments, Jackson and his co-workers found that ants do exactly that and manage to figure out the right direction.

Angles and degrees

“We found that it isn’t the pheromones themselves that determine direction but the angles that they are laid in. The trails are laid at 60 degree angles across the whole network. This means that the ants can tell which way they are going along any trail in the network.” Their experiments showed that ants performed best at figuring out the direction when the bifurcation had an angle of 60 degrees. Interestingly, their natural trail networks also have bifurcation angles of 60 degrees.

So, the Pharaoh’s ants know geometry. So what? Well, this species also happens to be one of the worst pests worldwide, although their place of origin is North Africa. In 1758, when Carl Linnaeus, the father of modern biological nomenclature named this species Monomorium pharaonis, he mistakenly thought this ant was one of the plagues of Egypt mentioned in the Bible. Little did he realise that this ant would spread throughout the world like a plague, following man everywhere he went. The financial damage caused by invasive species of ants is now estimated to run into billions of dollars.

Scientists say that unique abilities such as what we saw earlier, might give invasive species an advantage over other species, resulting in their colonising new environments. Studying the abilities of such invasive species offers new insights into their functioning and might lead to the design of effective strategies for their control. But, for now, the Pharaoh’s ant seems to rule the world and it might be a very long time before we will be in a position to say, “The Pharaoh’s ant is dead, long live the Pharaoh’s ant!”

(Published 11 January 2010, 09:46 IST)

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