Sick Ant Pupae Can Signal Workers to Kill Them with a Unique Odor to Save Their Colony, Study Finds

In a striking example of biological self-sacrifice, sick young ants may effectively signal for their own death to protect the rest of the colony from a deadly infection, according to new research.

A study published in Nature Communications on Tuesday, Dec. 2 reports that ant pupae infected with a lethal pathogen can release a distinct chemical cue — one that healthy worker ants interpret as a warning to eliminate the infected individual before the disease spreads.

Animals that live in groups (including humans) often try to hide illness to avoid being shunned or attacked. But for social insects such as ants, the rules are different: the colony’s survival depends on shutting down outbreaks fast. Ant colonies operate like “superorganisms,” where individual survival matters less than the well-being of the whole. The new findings suggest some ants take that idea to an extreme.

The research examined Lasius neglectus, a species of garden ant. Adult workers that become severely ill can leave the nest and die away from others, reducing risk to nestmates. But pupae can’t do that. They are immobile, sealed inside cocoons, and remain in the nest — which means an infection in a pupa can become a serious threat to everyone around it.

When the pupae were infected with a fungal pathogen, researchers observed chemical changes on the insects’ outer surface that produced a recognizable odor. Worker ants detected the unfamiliar scent, removed the pupae from their cocoons, and then bit into them to deliver an antimicrobial poison — a response that both disinfects and kills the infected pupae. As the study explains, “This process prevents pathogen replication in the host and ultimately limits its spread throughout the colony.”

Crucially, the researchers say this odor isn’t just a passive byproduct of being sick. Evidence suggests it functions as an active signal produced by the pupae — and only under the right social conditions. In controlled experiments, scientists transferred the chemical signature from infected pupae onto healthy ones, and workers responded the same way, destroying the otherwise healthy pupae. Meanwhile, pupae kept away from workers did not produce the scent, reinforcing the idea that the chemical cue operates as a deliberate “find-me and eat-me” signal, as described by the Austria-led research team, according to CBS News.

Lead author Erika H. Dawson of the Institute of Science and Technology Austria said the behavior reflects altruistic disease signaling: by sacrificing themselves at a terminal stage of infection, pupae reduce the chance the pathogen will spread through the nest, protecting close genetic relatives and the colony’s future.

The study also found an important exception. Queen pupae — future reproductive individuals — do not appear to emit the same signal when infected. Researchers suggest that queens may have stronger immune defenses and a better chance of surviving infection, making self-sacrifice less advantageous. There’s also a bigger risk: if workers kill a future queen too early, it could undermine the colony’s long-term reproductive success.

Overall, the findings add depth to scientists’ understanding of “social immunity” — the group-level defenses eusocial species use to control disease. By signaling infection when the threat is greatest, ant pupae may help protect the superorganism — even when it costs them their lives.