Territories

Ant colonies can control vast areas in which they hunt and gather material for the nest. But to control and keep territories is no easy match, as there are almost always other ants around ready to fight for it.

territories ant colony fire ants wood ants solenopsis pheidole

Ants have no conscience. They kill without hesitation, wether it is insects or other ants (even their own species). The only thing that matters to them is the colony and its survival. Considering this aggressive behaviour it comes as no surprise that ant colonies are at constant war with other colonies. So, what do they fight about? Mostly it’s about food – and territories are the same thing as food supplies.

As Hölldobler & Wilson suggests in their book Journey to the Ants: if ants had nuclear weapons, they would probably destroy the world within a week (1). And there is not much to argue with there. Ants are terribly ferocious warriors, and they never give up. They can destroy a colony and not give up until the last enemy ant is dead, and then simply move on to eliminate the next threat.

The Fight for Territories

In the southern US, there is a good example of the territorial conflicts between ants. This case is all about Solenopsis invicta (fire ants) and Pheidole dentata (woodland ant). The fire ant is imported while the wood ant occurs naturally in the area. When compared, one quickly discovers the Pheidole not standing a chance. The Solenopsis-colonies can grow up to one hundred times larger than them, and they are deadly enemies. But in spite of this both species are prospering in the region. How come?

The Pheidole, even though lesser in numbers, have a secret weapon: a solider caste. The soldiers have giant heads with enormous mandibles and work as great defence against invading enemy ants. They are the special forces of the colony – their super ants. They make out about 10% of the colony and uses their jaws to sever enemy legs, heads and bodies.

While the soldiers hang out by the nest, the regular workers are busy scouting the territories for new sources of food or signs of enemies – mostly fire ants. When a Pheidole worker meets the same from a Solenopsis-colony, the former lashes out against the latter. Not to kill it, but rather to get a sample of its scent. When having accomplished this the worker runs back to its mother colony of Pheidole, all the while alarming everyone with warning-pheromones that ”an enemy is near!”. She informs passers-by of the threat by combining the scent sample of the enemy with her own warning-scent. This way the Pheidole workers quickly gangs up to kill the enemy. And within minutes it is found and eliminated. This quick way of reacting is incredibly important to the survival of the Pheidole. If the fire ant would be free to go, it would quickly return to its home and bring back an army. If this happens, the Pheidoles are doomed. This is why the strategy of patrolling the territories is an extremely important task for the survival of this species.

If fire ants slips away from the effective wood ant defence, and returns home to deliver their coordinates, an attack will be initiated. The Solenopsis will spread like wildfire over the territories of the Pheidole and kill everything in its way. With the help of acid in their abdomens they easily kill the workers and can even take on the soldiers. The workers of Pheidole dentata can be compared to the warriors of ancient Sparta. Despite the Solenopis having the upper hand, they will fight until the last man (or woman in this case). They are programmed to defend the colony, and will fight till death. When the fire ants have the colony surrounded, the activity in the nest will step up. All of a sudden the nest will explode with workers, running around in panic – trying to get away from the battlefield. They carry what they can and tries to save brood. This situation is not very common in the ant world, because it’s every ant for herself. Even the queen runs alone.

When the fire ants have won and abandoned the site, the survivors of the wood ants will return. After a few months the nest will be back to normal, as if no invasion ever took place. The Pheidole will not avenge their fallen sisters, but rather keep going trying to make the most of their lives. A great example of how man and ant may differ. (2)

References:

1. Bert Holldobler & Edward O. Wilson (1995) “Journey to the ants” p. 59

2. Bert Holldobler & Edward O. Wilson (1995) “Journey to the ants” p. 60-63

Further reading:

Experimental analysis of territory size in a population of the fire ant Solenopsis invicta – //beheco.oxfordjournals.org/content/14/1/48.full

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