* Manoj Pandey
Ants are everywhere. So, it is unlikely that you have not seen ants in your kitchen, dining tables and even beds. You might have suffered itch and red skin when a tiny red ant bit you. Chances are that, if your profession is not of studying ants or you have not been too inquisitive about them, you would have ignored them as minor pests.
But ants are not so mean when it comes to their social structure and functions. They are much more socially evolved than other animals around us; and they accomplish great tasks, going by their tiny size and minuscule brain. Let us look at a few fascinating aspects of ant life.
Too many, too varied!
Though ants look alike, there is a wide variety within the ant population. About 22,000 species of ants have been recorded.
Some ants are big, and their ‘queen’ can be as big as a human finger. Other ants are just a few millimetres long, and some are even less than a millimetre. Some live in colonies of thousands while a few species have just a few dozen members in one colony.
Ant nests can be simple or complex. In most cases, they make nests under leaf cover (in forests) or underground. Some live in tree crevices, some make nests out of leaves stitched together, and some even join together to make a nest!
Most underground ant nests start with a narrow opening, which branches out to tunnels. Some ants can have thousands of small connected chambers that run several metres deep.
A few types of ants are known to make clusters of colonies, in which worker ants can move into others’ areas. These supercolonies may be as big as football fields. A few among have supercolonies that spread over hundreds of kilometres. One such structure is known to be 6,000 km long and spread from Italy to Portugal!
Then there are ants that do not make permanent nests. Such ants are mostly raiders, which raid an area, settle for a small period for laying eggs and tending till they turn into young ants, and then move on to a new area.
Most ants are moderate in their eating habits. They are scavengers, picking up whatever food is available in their surroundings. Their food consists of dead plant and animal parts, and plant products (e.g. honey, fruits, grains). They are not too aggressive. They also have adapted well to human habitations, even with growing urbanization.
Though all ants bite and sting, they are not too poisonous. Among highly poisonous ants, an Australian species can kill a human being in fifteen minutes.
Ants are great weight-lifters. Considering that a normal human being can lift at most 2-3 times their body-weight, it looks hugely impressive seeing some draught animals being able to carry objects 30-40 times their own body’s weight, isn’t it? Now look at ants: some of them can lift up to 5,000 times their body-weight!
Some ants are known to grow fungus and some tend livestock! Some types of aphids are ants’ main pets. Ants get a sugary substance from them and in return protect them from predators and even care for their eggs. However, they do not allow aphids to fly away, by secreting a chemical that stunts aphids’ wings.
Some ants have extreme habits. There are about 200 types of ‘army ants’, which are brutal invaders. These ants move in big numbers and raid colonies of other animals, including ants, and can kill much bigger animals within no time. South American army ants swarm their target area with exceptional ferocity, and kill whatever animal comes in their way. With around two lakh ants participating in a raid, the swarms can be many metres wide and long. The ‘leafcutter’ ants of Central and South America can cut all the leaves of a big tree overnight, and store the leaf-pieces in large heaps in their nests. These ants are known to grow fungus in their colonies. A group of ants are ‘trained’ in doing the job of cutting leaves finely and spreading fungus on the pieces. The fungus generates nutrients out of leaves, which the ants use.
By the way, can you guess the number of ants in our planet? I bet, you can’t.
A 2022 study has estimated that there are about 20 quadrillion (200 crore crore) ants on the earth, and their total weight equals the weight of all wild birds and mammals combined, or about a fifth of all humans. They live in all regions of the world, except in lands with extreme climates.
Ant colony: a social structure with amazing nuances
In most ant colonies, there is a well-defined caste system in force. There is a queen, whose sole function is to lay eggs. There is usually only one queen in a colony, but colonies without a queen or with more than one queen also exist. The queen is fed and cared for by other females. Most of the members of the colony are workers – all females – and among them there are care-givers, cleaners, foragers and soldiers. Then, there are males, whose function is to fertilize eggs laid by the queen. All have their roles, which they perform without question. However, these roles are not cast in stone; if need be, the roles change. In fact, females perform different roles based on their capacity and age.
Smooth functioning of the colony needs that the roles are distributed properly among the individuals and the distribution of different castes is complementary. Otherwise, there would be conflict among castes, and chaos. And, yes, ant colonies have a near-perfect division of labour and optimal number of members in each category.
For example, young females have the responsibility to look after the queen and under-developed ants (mostly larvae). Slightly older ones feed the young ones. Adult females do all the work, such as exploring and collecting food, defending the nest, cleaning the nest and removing trash, digging ground for expanding the nest, and relief and rescue in times of disasters. Older adults are usually the ones that go out in search of food, and that is not a mere convention. In older age, they have well developed smell glands for communication, and they have more experience than the younger ones. They, thus, can guide the younger ones well. Besides that, hunting for food is risky, and numerous ants keep getting killed every day. In any case, the old ones would have died due to old age and become a burden to the colony. So, sending them away helps in giving space to new ones in the colony.
Especially in underground nests, temperature and humidity control is a fine art. Ants specialise in selecting suitable places for making their nests. The queen, larvae and young ones must be kept in humid and lukewarm temperatures so that they do not suffer from extremes of temperature and water stress. When there is excess of heat due to ants’ own activity, they seem to disperse, and in extreme cases, break the colony and relocate part of it in a new place. There has to be proper areas in the nest for storing food, especially for unfavourable seasons and weather.
What is narrated above is rather a simplistic framework in which most ants operate. In reality, the functioning and relationships are much more complex, even going by the few studies conducted so far on ants. Ants also vary a lot in their social structure – some colonies may have many queens or no queen, some have a more sophisticated hierarchy, in some ants males and females are produced in different ways, and so on.
Interestingly, ants do not have a sophisticated brain, nor do they have a complex genetic structure. In fact, ants have among the simplest genetic make-up. Males in common ants have a single chromosome (a thread made of genes in a living being’s cell; humans have 46 of them).
So well-developed social communication!
In an ant nest, small or big, numerous chores have to be done in tandem, and each chore is done without supervision or direction. If workers need to switch jobs to meet the ever-changing needs of the colony, that also happens without a central command.
Animals get sensory inputs from their sense organs. In humans, the eye is the most important sensory organ, and is supported by ear, skin and nose. In ants the eyes are specialized (like those in other insects) and they can see objects even in very low light. Some ants have been found to sense radiation beyond the normal light. On the other hand, workers in some ant species are blind or near-blind. Some ants are also known to make sound by rubbing their bodies in a way that would produce distinct sounds for alarm and friendship.
However, ants are believed to use smell much more than any other sensory input, including vision.
Ant bodies secrete many – about 25 found in a study – smelling compounds, called ‘pheromones’. These are chemicals with distinct smells. While one of them defines the colony, there are other smells for different tasks. Their presence (or absence) and relative concentrations, both seem to act as distinct signals. Together they make a sort of language for communication.
In a number of studies, it was found the patrolling ants (soldiers) secrete a pheromone that makes the foragers (food collectors) feel safe to go out. When foragers do not find such a pheromone in the surrounding, they are likely to remain inside and utilize their time in other jobs inside the nest. In a study, when scientists removed soldier ants from around the nest, foraging ants did not come out of the nest, and when soldiers were removed from within the nest, ants sensed a bigger danger and the entire colony fled from that place.
A 20-year study on ants suggests that smell not only plays a role in an ant’s individual life, job in hand and communication, but it has a very important role in the overall management of the colony. A worker ant is not supervised, and yet she knows what work to do and whether she is needed for a chore elsewhere, perhaps due to secretion of a particular pheromone by ants needing help.
It is amazing to see how the entire ant colony works as a unit. All tasks, be it foraging or exploring new habitats, moving their colony or raiding the prey, are highly coordinated.
It has now been established, through a number of studies, that ants have the ability to find the best route from the food point to their nest. It is found that some ants have the ability to find the best path based on their experience, experimentation with different available paths, gathering magnetic and visual signals, etc.
In common types of scavenging ants, the adult explorer (or a few of them) that finds the right way back from the food point becomes leader for that campaign. She trains a few other ants by making them follow her to and fro, and by communicating with touch. These new ants then become leaders for the herd. These ants signal the path to others by leaving a trail of a particular pheromone. The pheromone trails get reinforced as more ants use the same trail.
In ants that do not produce strong pheromone trails (for example, ants with very small colonies), there seem to be other ways to find best paths and communicate it to others.
The path chosen by ants for bringing food, relocation of the colony, etc. is often the shortest path. It is also interesting that ants choose a longer path when that is more energy-efficient and safe. If a large contingent is to move fast (for example, when relocating the colony), two or more paths are demarcated to reach the same point.
When a colony has to be relocated, it is a collective decision. Amazing as it looks, ants take that decision as if all their brains had combined to arrive at a decision. In one study, it was found that when the nest becomes warmer beyond a point due to growing colony size and weather, a decision is taken in which a section of the colony leaves the nest for a new place. Whether their smelling chemicals alone help in taking this decision (who will move away, when, where, by what route, and so on) is not known.
When a part or whole colony has been relocated, every member preforms his or her role, and the colony runs as before, with least disruption. In an experiment, it was found that almost a third of workers turn leaders during relocation, so that all others – most of them carrying broods (eggs, larvae, pupa) and stored food in their mandibles (appendages attached to their mouth) – carry out transportation in the shortest time.
There seems to be some additional mechanism to deal with regulation of mass movement. In some uncoordinated tasks in the field, ants work at cross-purposes at times, for example in pulling a fallen prey to different directions. However, when it comes to moving in large numbers or carrying a huge prey to the nest, their coordination is amazing. They also follow a lane system so that onward and backward moving ants do not bump into each other. When huge contingents of army ants move, the ones who have found food follow a return lane while others march on.
The world of ants looks even more fascinating when we try to unearth the ‘humane’ qualities of individual ants: how they tirelessly care for the young ones, bring home the injured, collect food for all without favouring anyone, offer their bodies for making bridges and boats for others, and so on. Maybe there are rogues among them and there is a way to deal with them. Some types of ants commit mass suicide. Their chemistry with their pet aphids is also remarkable. There are many known, and unknown, facets of the life of this creature that looks so insignificant. There is something extra-ordinary in the ant, which leads to its robotic precision in doing things, unfailing loyalty and an extreme sense of altruism. Let’s talk about that some other time.
The living world is full of wonders. If you are interested in exploring how some birds migrate long distances every year and are able to return to the starting point with uncanny precision, consider visiting this link: A bird that flies from one pole to the other to greet the midnight sun!
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