Ants are being recruited as soldiers in the human war against resistant superbugs.
Scientists have identified ant species that make powerful antimicrobial agents for their own protection.
Experts hope that in future they will provide a much-needed source of new antibiotics to replace those that are rapidly proving ineffective.
Researcher Dr Adrian Smith, from North Carolina State University in the US, said: "One species we looked at, the thief ant (Solenopsis molesta), had the most powerful antibiotic effect of any species we tested - and until now, no one had even shown that they made use of antimicrobials.
"Finding a species that carries a powerful antimicrobial agent is good news for those interested in finding new antibiotic agents that can help humans."
The ants carry the natural antibiotics on the surface of their exoskeletons.
To test their effectiveness, the scientists used a solvent to remove the substances and introduced them to bacterial "slurry".
Bacterial growth was halted completely in the slurry containing thief ant antibiotic and slowed in other samples.
Twelve out of 20 ant species were found to carry some kind of effective antimicrobial agent, while eight did not appear to make use of antibiotics at all.
The research is reported in the journal Royal Society Open Science.
Dr Smith added: "The fact that not all ants use antimicrobials highlights the importance of refining our search for species that actually do hold promise for biomedical research.
"Next steps include testing ant species against other bacteria, determining what substances are producing the antibiotic effects - and whether ants produce them or obtain them elsewhere - and exploring what alternative strategies ants use to defend against bacterial pathogens."