How do Ants Communicate?


How do ants communicate? What are pheromones? How do ants use pheromones? What are the pheromones used by ants?

Ants are social insects, and, as a result, they communicate with each other.  Entomologists (those that study insects), and myrmecologists (those that study ants), have investigated communication among ants for more than 60 years.

Humans, too, are social creatures (well, we all know a few exceptions to this rule).  We communicate with each other using sounds and signals.  Ants have an analogous way of communication.  However, rather than using voice words, they use chemicals.  Pheromones to be more precise.

What is a pheromone?

The Oxford English Dictionary defines a pheromone as;   

A chemical substance produced, and released into the environment, by an animal, especially a mammal or an insect, affecting the behaviour or physiology of others of its species.

Ants have in the region of forty glands throughout their body.  Those involved in the production and release of chemicals, such as defence pheromones, include such exocrine glands as;

Mandibular gland (head).
Metapleural gland (thorax).
Pygidial (abdomen).
Poison gland (abdomen).
Dufour’s Gland (abdomen).
Sternal gland (abdomen).

These glands, between them, produce some 10-20 pheromones, depending on species of ant.

What do these pheromones do?

How do ants communicate?  Ants use pheromones to produce a range of signals which they use to communicate with other ants.  These signals include, but not limited to:

Alarm
Recruitment
Recognition
Group activity
Caste Allocation
Territory marking
Sex

Let us examine a selection of these.

Alarm

How do ants communicate? Alarms! 

Just as a police officer may use his radio to summon aid from other police officers, so ants use chemicals, or pheromones, to convoke its nest-mates.  Imagine an ant foraging for food in an area of ground close to its nest.  As the ant searches, a predator attacks it.  The ant does not have a voice with which to verbally shout, “Help!”, and unlike the police officer, the ant does not have a radio to call for help.  So, what does the ant do?  How can she call out for help?  This is where the alarm pheromone comes in.  When the predator attacks our ant, she will release a chemical, an alarm pheromone.  The pheromone diffuses into the air, carried by air currents, dispersing into an ever-increasing area.  Any ant nearby will detect the alarm chemical and react so.

As mentioned above, various species of ant use different chemicals or pheromones.  In 1970 a British entomologist, named, John Bradshaw, was studying an African species of Weaver ant.  He discovered that this species of ant released an alarm chemical consisting of four different pheromones, each with their diffusion rate.  The first pheromone caused nearby ants to move their antennae through the air as if sniffing the air around them; which is, in fact, what they are doing.  When the ants detected the second of the four pheromones, they began to run about here and there, looking for the source of the alarm.  On receiving the third pheromone they were able to home in on the source.  Finally, the fourth pheromones, when detected, made the ants more aggressive.

Often, when ants are alarmed, or in “aggressive mode” they will run about with their jaws menacingly wide open, ready to attack.

Recruitment

How do ants communicate?  Food!

I am sure you have seen a line of ants leading to and from a food source.  What is happening here?  How are the ants following this invisible line?  This is another factor we can discuss when answering the question of how do ants communicate?

When an ant leaves the nest to forage, it will navigate by various means, such as visual (though ants tend to have poor eyesight – some species are blind), ultra-violet light detection, and chemical trails.  Here I will focus on pheromones.

So, our ant is out foraging, looking for food to take back to the nest to feed the queen, the young, and her nest-mates.  Our ant finds a dead insect, one which she can easily carry on her own.  The ant picks up the insect and takes it home.  No help needed.  However, what if the food source is too big for her to carry back alone?  This is where pheromones come into play.  Our ant examines the food, tastes it, and eats some.  She then circles the area tapping the tip of her abdomen to the ground.  

Then she heads off for home, continuing to tap her abdomen on the ground.  What is she doing?  She is laying a chemical trail from the food back to her nest.  A fascinating factor at play here is that although our ant has taken a meandering course to find this food, she takes the shortest route home, in as straight a line as possible.

I often see my captive ants leaving a trail behind them when they make their way back to their nests, to report a food find.  The tapping on the ground of the abdomen seems far more pronounced, and, as a result, easier to notice in Myrmica species. 

 

Our excited ant runs home to tell her friends

As she rushes back home, she will greet her nest-mates in an excited flurry of antennal brushes and, sometimes, jerky, headbutting movements.  She is telling her nest-mate that she has found a food source.  The nest-mate will then tap the ground with its antennae and detects the chemical trail.  The ant lays the trail down in such a way that any ant finding it will know what direction to head in.

Once our ant reaches home, she alerts her nest-mates.  Very quickly, a line of ants form, from nest to food source, and back again.  As each ant returns home from the food source, so she will add to the chemical trail with her abdomen, thereby strengthening the scent trail.  This encourages more ants to follow the trail.

It is also interesting to note that often ants will form ‘lanes’ along the scent trail, to reduce collisions between ants, which would slow them down.  Soon there exists lines of ants following some sort of ant highway code, in which ants travelling in one direction will tend to stay on one side of the trail.  Whereas ants, travelling in the opposite direction will use the opposite side of the trail.  This tends to happen with particularly busy ant highways.

how do ants communicate?
Formica obscuripes nestmate workers engaging in trophallaxis, or the social sharing of liquid food. (Image: Alex Wild)

Recognition - Friend or Foe?

How do ants communicate?  Friend or Foe?

As mentioned earlier, when ants meet, they will stop to examine each other by touching antennae.  This is more than two ants saying hello to each other.  The ants are trying to determine whether the other is a nest-mate or not.  In other words, is this ant friend or foe?

Each ant colony has its own family scent, which every member of that colony will have.  A post-pharyngeal gland, found behind the pharynx, produces the scent.  The ants spread the chemical produced by the gland, over their bodies, and the bodies of their nest mates, as they groom themselves and others. Not only do ants have this colony scent, but each caste, in other words, each worker, soldier (not found in British species), male, queen, and brood type, has its unique identifying odour too.  This enables ants to determine not only if the ant is from the same colony as itself, but also what its caste is.

I stated above that ants can detect whether another ant is a nest-mate, and what caste it is of.  However, they cannot identify any particular individual within the colony. In the same vein, however, can ants identify which colonies non-nestmates hail from?

ants communicate
Friend or Foe? Dolichoderus inpai workers meet along a trail. (Image: Alex Wild)

Prof. Deborah Gordon Ph.D

In her 1999, book, Ants at Work, Prof. Deborah M. Gordon, Ph.D, professor in the Department of Biology at Stanford University, carried out an experiment with harvester ants, in which she sought to find an answer to this question. In this experiment, Prof. Gordon collected ants from various colonies that were found at varying distances from the colony she was currently studying. When she introduced the collected ants, in a controlled manner, to the one (home) colony, she found that the ants from nearby colonies were more likely to be attacked by workers form the home colony, than those from colonies further away.  Prof. Gordon suggested that ants found from nearby colonies were perceived as more of a threat, in the competition for food.  However, the ants from colonies further afield are considered lost, and therefore no real threat.

ants communicate
Friend or Foe? Dolichoderus inpai workers meet along a trail. (Image: Alex Wild)

Sex

How do ants communicate when it comes to sex? Ants mate during their synchronised annual nuptial flights.  However, it is only the winged alates who will mate, namely, the virgin queens and males.  The worker ants, who make up much of the colony population, are sterile females, and will never mate.

Everybody reading this has, no doubt, seen the phenomenon of the masses of flying ants that take to the air in the summer months.  This is the mating flights, triggered by two things, namely, weather conditions and pheromones.  For the past few weeks the new queens have been building up their body reserves and have doubled their weight since birth.  Now they, with their brothers, fly to mate with ants from other colonies of the same species.

The weather conditions must be ideal before the mating flights occur.  Preferably the queens will want to fly when there are fewer predators about, and when the ground is soft enough to excavate a chamber in.  The flights tend to occur on warm summer days, especially after a short shower of rain. Different ant species will fly at various times of the year, and at various times of the day.  Some species prefer to fly early in the morning, others in the afternoon.  Various species will fly as early as May, while others as late as October.

Male ants have no etiquette

Often the males will fly first, and it is believed they may release a pheromone as they leave, which provokes the queens to fly.  The males and/or the queens will emit a pheromone designed to attract a mate. Flying ants can fly one hundred feet or more into the air in their search for a mate.  However, ants cannot fly for too long, especially the males – an hour at the most.  The flying ants have a small energy reserve for flying, and once that is spent, they are forced to land.

The males will mate once, with one queen, though the males of a few species are able to mate more than once, but not usually more than twice.  The males have a limited sperm supply, and cannot produce further supplies, as their testes degenerate shortly after birth.   Once mating has occurred the males will very quickly die.

I have discussed here some of the pheromones used by ants, and their uses with the world of the ant.  There are many more that the ants use, however, I hope that the examples I have given above have been of interest for you. 

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