Ants produce ‘milk’ that nourishes both larvae and adults

Imagine an animal whose female offspring produce a highly nutritious type of milk, which is consumed by both babies and adults of the species. It sounds like science fiction, but that’s more or less what researchers in the US have identified in several species of ants around the world.

Experiments have shown that the secretion rich in nutrients is produced by the pupae of these ants (at the stage of development equivalent to the period of metamorphosis of a caterpillar into a butterfly). The adult ants place their larvae to “suck” in the pupae, and the mature individuals also swallow the secretion. If the liquid is not consumed, the pupae eventually die, which means that the process is crucial for all “age groups” of the nest.

The research, which has just been published in the scientific journal Nature, one of the most important in the world, could be an important milestone for understanding the evolution of the social complexity of ants. Food interdependence among anthill members over three important phases of their development could have reinforced the rigorous cooperation and division of labor that have characterized ant societies over the past tens of millions of years.

But if “nursing” is so important for ants, which have been among the most studied insects since the 19th century, why was nobody aware of its existence until now? “Sometimes it’s difficult to detect more subtle interactions amidst the buzz of the anthill,” he told Sheet the study coordinator, Daniel Kronauer, from Rockefeller University, in New York.

“Orli Snir, who is a postdoctoral researcher in my lab, had the ingenious idea of ​​placing individuals at different stages of development in social isolation, outside the colony. It’s a bit like taking apart a complex machine to try to see what each component of it does”, says Kronauer.

“That’s how Orli realized that the ant pupae secrete a fluid. Inside the colony, the liquid never becomes visible, because other members of the ant nest consume it immediately, preventing it from accumulating. That’s why no one had ever seen the secretion before.”

The first details about how the process works were obtained by studying the species ooceraea biroi, of Asian origin, who have a peculiar lifestyle. Instead of having a queen that lays all the eggs, as happens with many insects in the group, the common ants of the species are capable of laying eggs, which develop without the need for a male to fertilize them – the next generation, therefore. , resembles an army of clones, genetically nearly identical to their mothers’ generation.

“In most ants, the colony contains members from all different stages of development, such as eggs, larvae and pupae,” says Kronauer. “But in the case of O. biroi, young larvae are only present when colonies also contain older pupae but no other immature stages. Because of that, it probably became more obvious that there was some sort of interaction between the older pupae and the younger larvae.”

When isolated, the pupae only developed if the scientists were cleaning up the accumulation of fluid – otherwise, they end up drowning in it. The scientists then used a blue food dye to mark the secretion and saw that it was being consumed by both the adults and the larvae, which were placed in contact with the pupae to “suck”. Incidentally, access to the “milk” of the pupae greatly increased the survival rate of the larvae.

Which is not surprising, considering the results of the analysis of the composition of the liquid. It has been shown to be rich in all kinds of amino acids (the building blocks of protein), sugars and vitamins. The chemical composition of the secretion, at the same time, has similarities with the fluid produced by other types of insects during the “molt”, or exchange of the exoskeleton (protective shell), which occurs as they are growing.

And that may be the key to understanding the origin of the process. “Evolution normally takes advantage of mechanisms that are already present”, says the research coordinator. “In most cases, the fluid from the molt is reabsorbed and recycled. But in ants, however, instead of the pupa reabsorbing all the fluid, some of it leaks out of the body and can be consumed by the members of the anthill.”

The team’s bet is that the process could be common to virtually all of the approximately 20,000 species of ants that exist. That’s because, after working with the O. biroi, they examined four other species, belonging to each of the major evolutionary subdivisions of the group. Among them is the solenopsis invicta, known to Brazilians as footwash because of its painful sting. Both the footworm and the other species also produce the secretion, with a very similar chemical composition in all cases.

Brazilian researcher Rodrigo Feitosa, a specialist in ants at the UFPR (Federal University of Paraná), says that the results of Kronauer’s team are a milestone in studies on these insects.

“Orli’s work opens up a whole new universe of evidence”, says Feitosa. “Ant pupae have always been neglected in behavioral studies because they are considered passive members of colonies and, therefore, with little influence on social dynamics. The fact that pupae are capable of secreting a nutritional fluid that benefits larvae and adults and that, if not removed, causes the pupae to die, is a discovery that definitely expands our knowledge of social behavior in an unprecedented way.”