Confirmed: ants produce milk

So much so, in fact, that many drowned in it, Snir says, at least if they didn’t die from a fungal infection first. Was it an abnormal phenomenon due to the isolation of the pupae from the colony, or something completely normal that had gone unnoticed until now? To find out, Snir injected blue food dye into the opening from which the liquid came out and replaced the bluish pupae in the colony.

He soon observed the adult ants extracting the fluid from the pupae and swallowing it, as revealed by the blue color that spread through their intestines. In addition, they often deposited young larvae on the pupae, which also fed on the liquid; these also turned blue.

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A kind of social glue

The finding has surprised and delighted the world community of myrmecologists.

“This is a very robust and well-designed study,” says myrmecologist Laurent Keller of the University of Lausanne, Switzerland, who agrees that the phenomenon may be quite common.

Bert Hölldobler of Arizona State University, who has studied ants since the 1960s, says he once suspected there might be something about the pupae that attracts the adults.

(Related: Ants build bridges in the air with their own bodies.)

“I never took up this topic again,” he says; “although it stayed on my mind. I’m absolutely delighted that these researchers did it.”

A chemical analysis of the liquid revealed that, in addition to other waste products from metamorphosis, it contains all the essential amino acids, as well as multiple carbohydrates and some vitamins. The pupae of other insect species tend to reabsorb and recycle these nutritive fluids, Kronauer says.

The exchange of nutrients between the different life stages of ants may be the cause of the intensely social lifestyle that these insects have developed over millions of years, Kronauer and Snir suggest. “This makes ants at different life stages dependent on each other,” says Kronauer. “It’s a kind of social glue that holds them together.”

Adria Le Boeuf, a myrmecologist at the University of Friborg (Switzerland) who studies the exchange of nutritive substances between the larvae and adults of ants, agrees. They may have paved the way for the more complex behaviors she investigates, she adds. “This fluid may have contributed to the evolution of cooperative brood care. [de las hormigas], since it encouraged adults to take care of them. And once the ants started drinking it, that may have set the stage for the transfer of other things.”

Are a few sips of pupal fluid really the root of the ants’ growing sharing economy? Future research is likely to deepen the discoveries of one of the most studied and still very mysterious groups of insects on the planet.