Ants are among the most successful social insects, forming complex, efficient colonies. Their varied diets allow them to thrive in nearly every terrestrial habitat. While the typical ant diet consists of plant matter and other insects, the question of whether they consume their own kind is nuanced. The consumption of other ants, whether nestmates or rivals, is a calculated behavior driven by resource scarcity, hygiene, or warfare, reflecting the harsh realities of colony survival.
Why Ants Eat Their Own Colony Members
Consuming a nestmate, known as intraspecific necrophagy or cannibalism, is a survival mechanism occurring only under specific, stressful conditions. This behavior is primarily reserved for resource management within the nest. The most common instance is survival cannibalism, which takes place during periods of extreme starvation, such as winter dormancy or prolonged drought. When outside food is unavailable, the colony recycles the protein and nitrogen content from deceased members to sustain the living.
Nutrient recycling is relevant for the colony’s reproductive success. Queen ants practice hygienic cannibalism during the early stages of colony founding. When a queen detects larvae infected with a fungus or other pathogen, she consumes the sick offspring to prevent disease spread. This cleanses the nest and allows the queen to recycle the nutritional value of the infected larva into energy for new eggs. Studies show that queens who cannibalized infected larvae saw an increase in subsequent egg production.
A similar culling behavior is observed in worker ants. They may spray an infected corpse with formic acid before consuming it, essentially disinfecting the food source. This ensures nitrogen is not wasted, maximizing resource utility. Under duress, this instinct to recycle protein can sometimes lead to the consumption of healthy eggs or young larvae, a form of self-regulation that prioritizes the survival of the queen and adult workers.
Removing the Dead: The Role of Necrophoresis
Although ants consume their dead when starving, the default and more frequent behavior is necrophoresis. This specialized process involves removing deceased nestmates from living areas to maintain nest hygiene and prevent pathogen spread. The behavior is triggered by specific chemical signals released by the dead ant’s body.
When an ant dies, the protective chemical signature associated with life fades, and volatile compounds appear on the cuticle. The most notable are fatty acids, such as oleic acid and linoleic acid, which act as the primary chemical cue for death recognition. Once a living worker detects these substances, it is compelled to grasp the corpse and carry it away.
The worker transports the body to a designated refuse pile, often called a “midden,” located outside the nest entrance or in a disused chamber. This necrophoric response is an efficient form of collective immunity, isolating potentially infectious material that could harbor fungi or bacteria. In some species, the disappearance of compounds associated with life, such as dolichodial and iridomyrmecin, signals the death of a nestmate, leading to rapid removal.
Eating the Enemy: Inter-Colony Predation
While cannibalism within a colony is a necessity, consuming ants from a foreign colony is a regular occurrence falling under inter-colony predation or warfare. Ants are highly territorial, and conflicts often erupt between colonies over food resources and nesting sites. These “ant wars” can be intense and often result in the defeated colony being utilized as a protein source.
A prime example is the behavior of army ants, known for their massive swarm raids. Army ant colonies move constantly, and their primary prey consists of the brood (eggs, larvae, and pupae) of other ant species. Army ants overwhelm a rival nest, kill the adult defenders, and systematically carry the rival brood back to their bivouac to feed their own larvae. This provides a large influx of protein for the growing generation of the victorious colony.
Another form of external predation is seen in “slave-making” ants, which are specialized social parasites. These species raid the nests of other ants, killing adults and stealing pupae. While many stolen pupae hatch and become enslaved workers, a significant portion of the captured brood is consumed by the raiding ants for immediate nourishment. This aggressive interaction and consumption of the enemy’s young is a direct strategy for resource acquisition and colony maintenance.
The Typical Ant Diet
Instances of ants consuming other ants represent a small fraction of their overall nutritional intake, which is diverse and opportunistic. Ants are omnivores, and their diet is divided into two major macronutrient groups: carbohydrates and protein. Carbohydrates provide the quick energy needed for foraging, nest maintenance, and worker activity, and are primarily consumed by adult ants.
The most common carbohydrate source is honeydew, a sugary excretion produced by sap-sucking insects like aphids, which many ant species actively “farm.” Other energy sources include plant nectar, fruit juices, and tree sap. Protein is the primary food source for the queen, who needs it for egg production, and for developing larvae, which require it for growth.
Workers forage for protein by hunting smaller arthropods or by scavenging on the remains of dead animals. Once protein is brought back to the nest, the larvae act as a “protein stomach” to digest the solid food. The larvae then excrete a nutritious liquid that adult workers consume through trophallaxis (mouth-to-mouth feeding), ensuring all members receive necessary nutrients.