Ants vary considerably in their proclivity for violence. Depending upon species and colony size, ants adopt different strategies for attack or defense, ranging from duals to full-scale battles, even suicide attacks.
Fire ants often coexist in territories with numerous other ant species. When a competitor approaches, war is inevitable.
In temperate climates, especially as spring unfurls, when the brood are developing and insect prey are rare, warlike impulse arises. It may take less than an hour for 2 colonies to be on a war footing.
Battle preparation is judicious. Only up to 1/5th of a colony is recruited for war, in case a 3rd party attempts an incursion.
Soldiers join battle as aggressive accountants. An individual worker recognizes the smell of her cohorts.
As she carries on the fight, a soldier can get a sense of relative numbers. If outnumbered, communication between battling sisters lets them retreat en masse.
Battles usually last no more than a few hours. It is futile for a losing side to fight on. Winners have no interest in acquiring more territory than they can readily defend and exploit.
Some ant species have a special, morphologically distinct military caste. Mediterranean colonies of Pheidole pallidula have soldiers with larger bodies and heads than other workers. The larger head accommodates more powerful mandible muscles.
Battle engagements require troops. A colony that becomes aware of a neighboring nest can prepare for war by breeding a battalion.
Nursemaids can vary larvae feeding to foster additional soldiers. This comes at the expense of rearing workers of other castes. An ant colony is careful not to overexpend its military budget at the cost of homeland prosperity.
Formica polyctena, a northern European red wood ant, adopts a more ferocious approach at times. A nest may turn viciously nasty in early spring if food runs short: mounting implacable expeditions against rivals of their own species, as well as other ants, wiping out all in their way to total dominion of the local habitat.
Some ants have stings: used to protect against predation, defend territory, and capture prey. A Ponerine ant species in Southeast Asia uses its stinger venom differently depending upon the size of its adversary. Against a large arthropod enemy, a Ponerine stings to kill. If instead attacked by small Pheidole ants, a Ponerine spins filaments of venom to cover the attackers. The Pheidole – bogged down and covered in froth – instantly lose their aggressiveness.
Several social ants practice slavery of other colonial ant species. The woodland American slave-maker ant lives off its slaves, which are a different ant. The slavers do not forage for food, care for their brood, nor do they defend their nests. Instead, their slaves do the work. A small slaver colony has a solitary queen, 2 to 5 workers, and 30 to 60 slaves.
Slave-maker ants are bold raiders: preferring to attack larger colonies, though timing their attacks when the target nest has most of its workers in the field. Invading the nest, workers within are killed. The slavers steal larvae.
Enslaved worker ants care for the broods of both the slave-maker and the next generation of slaves; but only up to a point. Once larvae pupate, enslaved ants can tell by scent the emergent slaves from the slavers. A substantial number of slavemakers are killed by slave workers.
Slaver pupae are neglected, or actively attacked and torn apart. Several slaves may gang up on a defenseless pupa. Enslaved workers do not directly benefit, as they do not reproduce; but their sisters in the host nest are helped.
Slave-making colonies damaged by slave rebellions grow more slowly. Smaller slave-maker colonies are less audacious: conducting few raids with less destructive effect.
There are geographic differences in the strategy of those subject to enslavement. Potential slave ants in New York are especially aggressive, often able to thwart raids. In West Virginia, rebellion is more common, as neighboring colonies are often closely related to the slaves.
Ants willingly sacrifice themselves for their colony. At the extreme, the carpenter ant (Camponotus saundersi), endemic to the forests of Malaysia and Brunei, is a built-in bomb. This carpenter ant has 2 enormously enlarged mandibular glands that run the length of its body. These glands produce a peculiar defensive substance.
If losing in combat, a worker violently contracts its abdominal muscles, rupturing its gaster (rear segment) at the intersegmental fold. This also bursts its mandibular glands.
A sticky secretion spews in all directions from the front of the ant’s head. This corrosive glue and chemical irritant entangles and immobilizes all those nearby.
Some ants avoid fatalities when faced with an adversary of the same species. In a conflict over foraging territory, honeypot ants engage in ritualistic tournaments. A single ant can trigger a tournament, which can grow to several hundred being involved, as scouts recruit participants.
Workers scurry about, swelling their abdomens and stretching their legs, trying to look larger than they are. They further the illusion by seeking higher ground, such as standing on pebbles.
When 2 adversaries confront one another, they jostle for a few seconds, until one gives up. The two continue to the next contest, until one side prevails by numerical tally. Recruiters keep count.
The losing side quickly senses if a contest is too uneven. They retreat to their nest, close off the entrance, and hide out until the rivals have left. If they are not fast enough, the larger group will raid the smaller colony’s nest: stealing stored food, abducting larvae, and killing queens.
As a matter of practice, honeypots are highwaymen: stealing food from other ants. Pogonomyrmex, a harvester ant, collects seeds and an occasional termite. If caught by a honeypot, the harvester is robbed of its abducted termite.
Pogonomyrmex is not defenseless. Its venom is quite toxic: many times that of the honeybee, comparable to a cobra snake. But Pogonomyrmex reserve their sting for predators, notably horned lizards. Losing a stolen termite is not worth incurring the wrath of honeypots.
Honeypot ants are themselves victimized by minute Forelius pruinosus ants. These tiny terrorists use toxic secretions to intimidate and seize honeypot reserves.
F. pruniosus sometimes employs a more ambitious stratagem: they gather in hordes at honeypot nest holes, using their chemical weapons to force the bigger ants underground. With the honeypots cleared from their hunting territory, Forelius can harvest a larger share of available food.
Looting is an unexceptional ant behavior. For one, the endemic British thief ant is a large-scale looter. Workers dig a network of tunnels joining their nest to a neighbor to be invaded. Upon penetrating their victim’s colony, thief ants fend off defenders with chemical repellants. The thieves snatch brood grubs and carry them back to their nest for food stock.
A cunning precaution that thief ants take is to make their escape passages too narrow for dispossessed victims to pursue them. Thus, the thieves make off with their booty without fear of reprisal.
Within a species, different colonies of ants have different levels of aggressiveness. A colony has its own individual character, reflective of the queen(s).
There are also distinct personalities within an ant colony. Some individuals are naturally more aggressive than others.
Ants in a colony typically swarm to attack an intruder. It is a select group that call themselves to combat, even among ants that don’t have specialized castes.
Aggression reflects colony division of labor. Variability in behavior patterns is an important element in a colony’s success.
While aggression is common among ants, some species never attack. Their posture is always defensive.