Megaponera analis is no ordinary ant. Whereas its 13,000-odd cousins enjoy a varied diet, it is picky and eats only termites. But, as the latter don't take kindly to it, worker raids present serious risks: almost 22% of attackers are injured. In a remarkable thesis, presented in a book (Combattre, sauver, soigner, CNRS Editions, 2020, "Combat, Save, Care") as well as a documentary (Life on Our Planet, streaming on Netflix), biologist Erik Frank – from the University of Würtzburg, Germany – had already shown how the most affected ants sacrifice themselves to preserve the colony. But what happens to the others? How do they heal themselves? To find out, the researcher spent three years between his observation field in Côte d'Ivoire and the Université de Lausanne, Switzerland. The result, published in Nature Communications on December 29, 2023, is astounding.

On their return, the injured ants first undergo a medical examination. The aim is to differentiate between those with sterile wounds, which are likely to heal on their own, and those with infected wounds. To do this, they use the hydrocarbons present on the cuticle of the patient. This lipid layer protects all insects from drying out. In ants, it is also a chemical signature. "It allows a distinction between members of the colony and outsiders, and also an identification of the status of each ant: nurse, hunter, queen," Frank explained. This "kind of uniform" does even better: it tells the nurse ants – and this is the first previously unpublished result of the article – whether or not the injured subject has activated its immune system; in other words, whether or not it is suffering from an infection.

The German-Swiss team proved this by infecting ants with the bacterium Pseudomonas aeruginosa in varying doses. At very high doses, the wounded ant was simply expelled from the ant farm; at very low doses, it was left to fend for itself. Between these two extremes, the nurses took charge. First, with all due respect to La Fontaine, they danced: they contorted themselves to allow their legs – the right, then the left, then the right, then the left – to reach the metapleural gland hidden in their backs. Then they licked their legs and finally applied what looked like a miracle ointment with their mouths.

Analysis revealed no fewer than 112 chemical compounds and 41 proteins therein, four times more than in other species. Effectiveness was undeniable. The researchers compared two ant colonies. In one, they left the nurses' metapleural glands accessible; in the other, they obstructed them. The result: of the infected and treated ants in the first colony, 75% healed. All those in the second died within 36 hours.

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