Amazing news from ant research: The pupae of social insects produce a milk-like substance that other members of the colony drink. The scientists were able to show that the larvae in particular need the nutrient-rich liquid to grow. The "milking" is apparently also vital: If the liquid is not absorbed, the pupae become moldy. This concept seems to be common to all groups of ants. The surprising new findings now help to understand how the fascinating insect communities evolved and are organized, the researchers say.
They shape our planet like hardly any other group of insects: Many different species of ants have conquered the most diverse habitats in the world and play an important role in ecosystems. Because of this importance, ants have long been the focus of research - and also because of their fascinating way of life. Because of their complex organization, the ants of a colony form an amazing unit: division of labor, exchange of substances and transmission of information - the diverse interactions of the individuals with one another create a system that is referred to as a "superorganism". Researchers are gaining more and more detailed insights into this fascinating concept. On the other hand, one might think that there are no longer any fundamentally new discoveries among ants. But what the scientists led by Orli Snir from Rockefeller University in New York have now uncovered is "Big News" in ant research.
What is collecting there?
As the team explains, the phenomenon has apparently been overlooked so far due to the fast pace of interactions in ant colonies. Initially, the scientists only found out about the "pupa milk" indirectly as part of studies on a model ant species: In order to investigate reactions to isolation, they removed individuals in various stages of development from the colony and observed them individually. Background: Insects undergo a complete metamorphosis during their life cycle. She begins with eggs that hatch into worm-like larvae that are tended and fed by worker bees. These "babies" then develop into fully formed ants during an immobile pupal stage. In studying the responses to isolation, Snir noticed something surprising about these dolls: the researcher discovered accumulations of fluid on their immobile bodies.
The researchers explain that insects in the pupal stage do not normally excrete anything, and such fluid had not been observed in ants before. It was also shown that these secretions can lead to the growth of problematic fungi: only when Snir manually removed the liquid did the pupae survive to adulthood. So it was obvious that this liquid is normally removed by maintenance measures in the colony. The scientists then systematically followed this lead: they observed the interaction of workers with the pupae. They also conducted dye trail experiments to find out where the liquid went. It finally turned out that adult ants absorb the substance and sometimes pass it on to the larvae. In addition, the little ones also pick them up through direct contact with the pupae, according to the observations.
In the next step, the researchers looked more closely at what the liquid was all about and what role it played for the ants. It became clear that the liquid originates from a process that occurs in all insects in the pupal stage: it is formed during the moulting process. While other insects immediately absorb the resulting liquid to recycle the nutrients, ant pupae appear to share it with their nestmates, the results show. Analyzes confirmed that the molting fluid is rich in nutrients and substances such as hormones that may have important functions.
Parallels to milk
This was confirmed by further investigations: If larvae do not receive the liquid in the first four days of life, growth is impaired and many die. "In the first few days after hatching, the larvae depend on this substance - apparently similar to how a newborn depends on milk," says senior author Daniel Kronauer from Rockefeller University. "Although it is not clear what the liquid does in the adult animals, we are sure that it also has an effect on their metabolism and physiology," says the scientist. It's not just a single-species phenomenon, either, the team demonstrated: researchers found the concept in representatives of all five major ant subfamilies, suggesting it's a fundamental strategy. "It probably evolved once - early in the evolution of ants or even before that," says Kronauer.
As the researchers point out, the discovery is an important aspect that contributes to the understanding of the complex interaction systems in the ant "superorganisms". "This reveals a new aspect of the interdependence between larvae and pupae and pupae and adults," says Snir. "The social pupal fluid is the driving force behind a central and previously overlooked interaction network in ant societies," states the researcher. In further investigations, the team is now planning to examine the importance of the pupae's milk for the ant colonies in more detail. Among other things, they want to find out whether the liquid plays a role in deciding whether a larva will develop into a specific caste in the ant colony. "Our long-term goal is to gain increasingly detailed insights into the mechanisms that control social organization and how these systems have evolved," says Snir.
Source: The Rockefeller University, professional article: Nature, doi: 10.1038/s41586-022-05480-9