The extent to which ants work together as a unit has led some scientists to consider them to be one superorganism.
But for all the focus on the ants’ frantic activities, researchers have rarely focused on the ants’ pupal stage, during which they metamorphose from larvae into adult ants.
“They don’t move, they don’t eat, they don’t do anything that’s obvious amid all the hubbub going on in the colony,” says Daniel Kronauer of Rockefeller University in New York, who’s a myrmecologist, the term for scientists who study ants.
In a new paper published this week in Nature, Kronauer and his colleagues report that often-overlooked ant pupae provide a crucial service to the colony: Their developing bodies make a milk-like substance that provides important nutrients to the rest of the colony. And not just in one species, but in at least one species in each of five major ant subfamilies.
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Such a wide-reaching discovery suggests the milky excretions may be common in many more ant species, Kronauer says, and that they may have originated early in the evolution of all ants.
“I was surprised,” says Susanne Foitzik of the University of Mainz in Germany, who was not involved in the study, “as I did not see this before, despite watching ants for three decades. I am really curious and will start my own observations as soon as possible.”
Drowning in milk
The intriguing liquid was discovered by Orli Snir, a postdoctoral fellow who had not worked with ants before she joined the Kronauer lab. With fresh eyes, she quickly noticed behaviors that didn’t seem to be explained by the existing scientific literature.
“People have studied ants for a hundred years,” Kronauer remembers thinking, “so what is [Snir] talking about?”
But he did agree when Snir proposed an unusual experiment. Instead of trying to make sense of the combined activity within the colony, where pupae and larvae are constantly being groomed, moved around or even piled together, she decided to watch the pupae in isolation. It took time to figure out how to keep them alive, but eventually, she found the right temperature and humidity level. Then, something really weird happened: the pupae were producing a liquid, and lots of it.
So much, in fact, that many were drowning in it, says Snir, at least if they didn’t die from a fungal infection first. Was this an abnormal phenomenon due to the pupae’s isolation from the colony, or something entirely normal that had gone unnoticed until now? To find out, Snir injected blue food dye into the opening where the fluid was coming from and put the bluish pupae back in the colony
