Terminally ill ants ask workers to 'kill them' in order to save the colony

Ant colonies run like living bodies. Queens produce offspring. Workers clean, feed, and defend. And brood develop quietly in the nursery. When disease slips in, the whole “superorganism” is at risk.

New research shows just how far ants go to head off catastrophe: terminally infected pupae change their body scent to broadcast an unmistakable message – come find me, disinfect me, and, if necessary, end me.

The result is swift triage that protects the colony’s health, even at the cost of individual lives.

Ant sickness becomes a warning

Many social animals try to mask illness to avoid exclusion. Ant brood do the opposite. As the authors discovered at the Institute of Science and Technology Austria (ISTA), pupae facing an uncontrollable infection actively signal that they are a danger.

The warning isn’t a dramatic alarm call. It’s chemistry. Their body odor shifts in a way that nestmates recognize with precision.

“What appears to be self-sacrifice at first glance is, in fact, also beneficial to the signaler: it safeguards its nestmates, with whom it shares many genes,” said first author Erika Dawson, a former postdoctoral researcher at ISTA.

“By warning the colony of their deadly infection, terminally ill ants help the colony remain healthy and produce daughter colonies, which indirectly pass on the signaler’s genes to the next generation.”

That logic – gene-level payoffs for individual loss – frames the work as the first detailed description of altruistic disease signaling in social insects.

Fast disinfection saves ant colonies

Once workers detect the altered scent, they don’t hesitate. They tear open the pupa’s protective cocoon (“unpacking”), nick the cuticle to create tiny openings, and flood the body with formic acid – the ants’ own antimicrobial poison.

It’s a brutally efficient disinfectant, lethal to the fungi or bacteria multiplying inside. It’s also lethal to the pupa.

The trade-off is clear: a single death now to avoid many deaths later. If a moribund pupa dies undetected, pathogens can explode in number, turning the nursery into an outbreak zone.

By pushing a chemical “help me, remove me” button, the infected brood prevents that chain reaction.

Ant colonies echo immune defenses

The study leans into a striking comparison. Colonies and bodies share a basic design: reproduction is concentrated (queens in nests, germline cells in gonads), while maintenance is distributed to non-reproductive workers or somatic cells.

Both systems depend on cooperation and tight communication to stay alive. And both employ a familiar tactic when parts become dangerous – find them and eliminate them.

“Adult ants that approach death leave the nest to die outside the colony. Similarly, workers that have been exposed to fungal spores practice social distancing,” Cremer said.

“Yet, this is only possible for mobile individuals. Ant brood within the colony, like infected cells in tissue, are largely immobile and lack this option.”

Immunologists call the chemical summons that draws immune cells to doomed tissue a “find-me and eat-me signal.” Ant brood, it turns out, have evolved a parallel solution.

Sickness leaves a scent

The team’s collaboration with chemical ecologist Thomas Schmitt at the University of Würzburg revealed how that signal is packaged.

It isn’t a wafting perfume that fills the nest (since workers target specific pupae within a pile), so the cue can’t be a volatile gas. Instead, it’s a change in the nonvolatile hydrocarbons coating the pupa’s surface.

Two components of the ants’ natural scent profile spike in intensity when a pupa is terminally ill.

To test causality, the researchers did something elegant: they extracted the odor from signaling pupae and applied it to healthy ones.

The ants responded exactly as if those healthy pupae were infected, proving the altered body odor is sufficient to trigger the colony’s emergency protocol.

Precision guides ant colony action

Crucially, the chemical cry for help isn’t indiscriminate. The team found that queen-destined pupae (those equipped with stronger immune defenses) did not emit the warning odor and could suppress the infection themselves.

Worker brood, which lacks those robust defenses, signaled when the pathogen was beyond control.

That nuance matters. If the cue were too sensitive, healthy or recoverable brood would be sacrificed unnecessarily; if it were too lax, and infections would slip through.

The ants have tuned the system to catch truly terminal cases while sparing those capable of recovery.

Social immunity, by design

The work reframes social immunity not as a loose set of hygienic habits but as a coordinated, multilevel defense.

At the colony scale, workers deploy disinfectants, manage brood, and isolate threats. At the individual scale, terminal brood flip a chemical switch that recruits that care, and accept the consequences.

“This precise coordination between the individual and colony level is what makes this altruistic disease signaling so effective,” Cremer said.

It also explains why such a system would evolve. Colonies with early-warning brood and decisive workers are more likely to survive outbreaks, produce daughter colonies, and spread their genes. The individuals that trigger their own removal still “win” in evolutionary terms, because their kin do.

Cooperation ensures colony survival

Seen alongside the body’s immune response, ants offer a vivid lesson: complex life depends on ruthless clarity about when parts become liabilities.

Cells turn on death programs; brood broadcast their doom. In both cases, a swift, targeted response preserves the whole.

That this choreography is mediated by chemistry – tiny shifts in waxy hydrocarbons – speaks to the sophistication of insect societies. The message is invisible, the outcome unmistakable: find me, end me, save us.

The study is published in the journal Nature Communications.

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