Dying for the nest: Sick ants choose the colony over life

Illness usually brings trouble in the animal world. A weak member may be pushed aside, attacked, or left behind. Many animals go to great lengths to hide sickness. But for creatures bound by family, the rules change. When relatives share genes, helping a sick member can protect the future of the group.

Ants take this idea further than anyone thought.

Scientists studying invasive garden ants discovered something that feels almost human in its logic. When certain ant pupae realize they are dying from infection, they send a message that leads to their own destruction. They do it to save the colony.

The study focused on the species Lasius neglectus and was published in Nature Communications. The work took place at the Institute of Science and Technology Austria and the University of Würzburg. It shows that some ant pupae can judge their own chances of survival. When those odds look bad, they call for help that comes with a deadly cost.

The ant nest runs like a living organism. Queens handle reproduction. Workers build, clean, and defend. The young remain inside the nest, unable to flee danger.

In many animal groups, sick members try to hide their condition. Ant brood, however, does the opposite. When an ant pupa catches a deadly fungus and can no longer fight it off, it releases a warning signal.

Workers respond with a swift routine known as “destructive disinfection.” They peel away the cocoon, make small openings in the body, and cover the pupa with formic acid. The acid kills the fungus. It also kills the pupa.

“What looks like self-sacrifice is also a genetic win,” said Erika Dawson, first author of the study and a former postdoc in the Social Immunity group led by Sylvia Cremer at ISTA. “By alerting the colony, the dying pupa protects relatives who carry the same genes.”

The workers act before the fungus becomes contagious. That timing keeps the nest safe. It also means the ants do not have to risk their own lives.

Researchers wanted to know if the signal was intentional or just a side effect of decay. To test that, they infected some pupae with fungus while keeping others healthy. Some infected pupae were placed with workers. Others sat alone.

If the disease alone caused the chemical change, both groups should smell the same. They did not.

Only infected pupae housed with workers changed the chemicals on their bodies. Infected pupae kept alone stayed chemically normal. That meant the pupae sensed the workers and altered their scent on purpose.

The key chemicals were two hydrocarbons found on the insects’ outer layer. Their levels rose only when an infected pupa shared space with workers. The amount of fungus inside the pupa did not predict the change. That ruled out simple decay. This was a message.

To confirm the role of the chemicals, scientists transferred the scent from sick pupae to healthy ones. Workers then unpacked the healthy pupae more often. Smell alone triggered the response.

“Transfer of the signal scent was enough,” Cremer said. “The altered body odor serves the same function as a ‘find-me and eat-me’ signal in human cells.”

Not all pupae made the same choice.

Ant colonies include two types of young: future workers and future queens. The difference mattered.

Worker pupae emitted the warning signal when infection took hold. Queen pupae did not.

Even when queens carried the same fungus, their scent did not change. Workers left them alone.

The reason came down to survival odds. Queen pupae showed stronger immune activity from the start. Their bodies fought harder and longer. In worker pupae, the fungus kept spreading. In queens, it rose at first and then dropped.

By the end of the tests, queens carried far less fungus than workers. They had a real chance to recover. Workers did not.

“It was not about emotion,” Dawson said. “It was about likelihood. Queens were likely to survive, so they stayed silent. Workers were likely to die, so they signaled.”

The warning scent was not simple. It came from two chemicals that appeared in many forms, known as isomers. One group surged nearly 20 times higher. Another rose about three times and shifted in balance.

One chemical alone meant nothing. Workers ignored it. Only the full blend worked.

The pattern varied across species. Honeybees use different signals. Termites rely on other chemicals entirely. There is no universal stench of disease in insects. Each species develops its own code.

“This signal must be exact,” Cremer said. “It needs to find all terminal cases without harming those that can still recover.”

Ant societies act like “superorganisms.” One death can protect thousands. That idea mirrors the human body, where sick cells signal the immune system to destroy them.

Ants reached the same solution through evolution.

Workers that are close kin and unlikely to reproduce are more willing to give themselves up. Queens, who carry the colony’s future, get every chance to live.

In the dark maze of a nest, chemistry decides fate. A blend of invisible molecules can mean rescue or ruin.

The discovery shows that ants do not merely react to disaster. They judge it.

Inside that small world, a vulnerable life can choose the colony over itself. That choice keeps the nest alive.

1. They farm other insects
Some ants raise aphids the way humans raise cattle. They protect aphids from predators and “milk” them for honeydew, a sugary liquid the ants eat. This gives the colony a steady food supply even when plants or other insects are scarce.

2. They create living bridges and rafts
When ants hit obstacles like water or gaps, they don’t just stop. Fire ants can lock together to form floating rafts during floods. Other species form bridges out of their own bodies so the colony can cross cracks and travel safely.

3. They build climate-controlled homes
Ant nests are not random dirt piles. Many species design tunnels and chambers to regulate heat, humidity, and airflow. Leafcutter ants, for example, build underground “gardens” to grow fungus for food and keep conditions just right for it to grow.

4. They communicate with chemical messages
Ants mostly “talk” using scent. They release pheromones to mark paths, warn of danger, call for help, or signal where food is. This chemical language lets thousands of ants act like one coordinated system.

5. They practice division of labor like a factory
Each ant job matters. Workers collect food, soldiers defend the nest, nurses care for larvae, and the queen lays eggs. Because everyone has a role, the colony can survive even if many individuals are lost.

Research findings are available online in the journal Nature Communications.

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