Ants can produce milk for their young (and old).

Researchers have observed for the first time that ants secrete a milk-like fluid that feeds others in the colony.

The study, published in Nature on November 30, shows that ant pupae—an otherwise inactive developmental stage—produce a nutrient-rich fluid that is ingested by both adults and larvae.

Newly hatched larvae depend on this fluid to grow and survive, much like mammalian newborns depend on milk. If the adult ants and larvae don’t consume the liquid, it accumulates and becomes contaminated with fungi, which kill the pupae.

“We identified a mechanism that unifies the colony and connects ants across all developmental stages – adults, larvae and pupae – into a coherent entity, the superorganism,” says co-author Orli Snir, a biologist at Rockefeller University in New York City.

“It’s really surprising that nobody noticed this before,” says Patrizia d’Ettorre, an ethologist at Sorbonne University Paris North, France. “The dolls were considered useless [because] They are immobile, in some species they spin a cocoon around themselves, they do not eat, they are only moved by the animals [ant] workers, so they [wouldn’t] contribute anything to the ant society. But this paper shows that is not true.”

Snir and her colleagues made the discovery by studying clonal predatory ants (Ooceraea biroi) kept isolated at different stages of their life cycle to study what makes ant colonies so integrated.

While observing isolated ant pupae, the researchers were surprised when droplets of a liquid appeared on the tips of their abdomens. As this liquid accumulated, the pupae drowned in it, but survived when removed.

By injecting blue food coloring into the pupae and tracing where it landed, the researchers showed that adult ants drink the liquid as it is secreted and also help their larvae drink it by carrying it to the pupae. This will prevent liquid from accumulating. “The adults provide parental care as they clean the pupae, take the larvae, and place them on the pupae to eat,” says Snir.

The team tested the liquid’s molecular composition and identified 185 specific proteins, as well as more than 100 metabolites such as amino acids, sugars and vitamins. The identified compounds suggest that the fluid originates from moulting fluids produced when the larvae shed their outer cuticle while developing into pupae. “It’s an opportunistic recycling that the ants engage in within the colony… and a metabolic division of labor,” says Adria LeBoeuf, a biologist at the University of Fribourg, Switzerland.

evolutionary role

The researchers also discovered pupal “milk” in species from each of the five major ant subfamilies, suggesting it may play a role in the evolution of ant social structures. “It’s something that evolved either shortly after ants became eusocial, or maybe even before ants became social,” says co-author Daniel Kronauer, a biologist at Rockefeller University.

The team now wants to study the effects that pupal secretions could have on the adults and larvae in terms of behavior and physiology. “Whether larvae [develop] in queen or worker could be modulated by how much access they have to this fluid,” says Kronauer.

Karsten Schönrogge, ecologist at the UK Center for Ecology & Hydrology in Wallingford, would like to see research “whether the secretion of the pupae is also useful for the transmission of microbial communities in the gut that help ants digest food”.

This article is reproduced with permission and was first published on November 30, 2022.

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