For more than a century biologists have believed that living organisms reproduce within their own kind, that a queen ant produces offspring of her own species, and that while hybridization can occur under special conditions, it remains an exception to the rule. A new study has now overturned that assumption with hard data, showing that a common Mediterranean harvester ant depends on a reproductive system that would have been dismissed as science fiction only a decade ago. In this system, a single mother gives rise to offspring belonging to two completely distinct species, and the survival of the colony depends on a cycle of cross-species cloning. This phenomenon has been formally described in Nature under the term xenoparity, a reproductive strategy in which females must create and sustain members of another species to complete their own life cycle.
The subject of this work is the Iberian harvester ant, Messor ibericus. At first glance these ants look no different from other members of the genus, living in large colonies across southern Europe and storing seeds in underground chambers. Yet population genetic analyses revealed something extraordinary: every worker in these colonies carries a hybrid genome, with half of its DNA derived from Messor ibericus and half from the builder harvester ant Messor structor. That alone was surprising enough, because the two species diverged more than five million years ago, and hybrid workers were being found in locations far outside the range of M. structor. On the Italian island of Sicily, for example, colonies of M. ibericus thrive despite the complete absence of local M. structor nests, and yet the workers still carry the genetic signature of both species.
The mystery deepened when researchers examined the sexual castes. Queens were clearly M. ibericus, but the males showed a striking dimorphism. Some were hairy, robust males consistent with M. ibericus. Others were nearly hairless, smaller, and genetically indistinguishable from M. structor. Both forms emerged from the same nest, and mitochondrial analysis confirmed that both types had mothers from M. ibericus. The evidence was clear: a single queen was laying eggs that hatched into males of two separate species.
To verify this conclusion the team monitored laboratory colonies under controlled conditions for nearly two years. Males are rarely produced in captivity, but with careful persistence they eventually witnessed the birth of males that could only be classified as M. structor, despite having been laid by a queen of M. ibericus. Genome sequencing confirmed that the nuclear DNA of these hairless males matched M. structor, while their mitochondria came from the queen. This combination could only arise if the queen was producing males by cloning sperm stored in her reproductive organ, the spermatheca, eliminating her own nuclear contribution and leaving only the paternal genome to guide development. In other words, the queen was directly producing sons of another species.
This reproductive system is unlike anything described in social insects before. While cases of androgenesis, in which males clone themselves using the eggs of another organism, have been documented in clams and conifers, those are instances of male parasites hijacking foreign eggs. In the present case the roles are inverted. Here it is the female who must propagate another species as part of her own cycle. By producing M. structor males, the queen ensures that her daughters can mate with them, and their sperm becomes the essential ingredient for creating hybrid workers. Without these cloned males, the colony cannot generate the worker caste, which is indispensable for foraging, brood care, and nest maintenance.
The consequences are staggering. Every colony of M. ibericus becomes a two-species superorganism, composed of M. ibericus queens and males, cloned M. structor males, and hybrid workers produced from the pairing of the two. The colony functions only because the queen provides all three of these elements. She lays new queens of her own species, she generates her own sons, and she also manufactures males of a foreign species whose sperm is necessary for the workforce. The hybrids themselves cannot reproduce, but they provide the labor that sustains the nest. What emerges is a reproductive triangle in which a queen becomes both the mother of her own kind and the obligatory producer of another species.
The evolutionary history of this arrangement appears to have begun with a form of sperm parasitism. In many harvester ants, queens mate with males from another lineage to produce workers, exploiting foreign sperm as a tool to bypass genetic conflicts that arise when mating with their own species. In M. ibericus, this dependence hardened into a necessity, as queens lost the ability to produce viable workers without foreign sperm. At first this would have tethered colonies to regions where M. structor was present. The breakthrough came when queens began producing M. structor males directly within their own nests. Instead of seeking out the males of another species in the wild, they created their own supply line through cross-species cloning. Over time this produced a domesticated lineage of M. structor males that are maintained only in M. ibericus nests and never seen mating with their own species.
The genomic data support this scenario. Cloned M. structor males show extremely low genetic diversity, far lower than wild populations, and carry a high load of harmful mutations, a pattern typical of clonal lineages. Morphologically they are distinct as well, consistently hairless compared with wild males, resembling domesticated animals that diverge from their wild counterparts through isolation. They cannot be considered a separate species, because their nuclear DNA clusters with M. structor, but functionally they behave as a domesticated line that has been absorbed into the reproductive cycle of M. ibericus.
This system raises profound questions about individuality and the definition of a species. Each colony contains genomes from two species, perpetuated together in a closed cycle. Queens control the production of both species’ males, regulate the timing of their development, and ensure that both lineages are available for mating. The hybrids, though sterile, embody the merging of the two genomes into a worker force that has no equivalent in either parental species. Biologists describe this integration as a major evolutionary transition, where separate entities become parts of a higher-level whole. In this case the colony itself becomes a reproductive unit greater than the sum of its species.
Such integration can be compared to the domestication of organelles in early eukaryotic cells. Mitochondria were once free-living bacteria, but were absorbed into larger cells and replicated within them. Here, M. structor males have been absorbed into the reproductive machinery of M. ibericus, propagated not in the cytoplasm of a cell but within the social structure of a colony. The analogy extends to the concept of organelles at the level of a superorganism, where an alien genome is replicated under the control of another species’ queens.
The research team coined the term xenoparity to describe this arrangement, from the Greek xeno meaning foreign and parity meaning to give birth. Xenoparity defines the necessity for a female to produce individuals of another species in order to complete her own reproductive cycle. It is not a mistake, not a case of parasitism alone, but a built-in requirement of the life history. To date this is the only known case of xenoparity in animals, and it challenges one of the longest-standing assumptions in biology: that mothers always give birth to their own species.
Beyond its theoretical importance, the discovery illustrates how evolution can create solutions that defy expectation. By giving birth to another species, M. ibericus queens solved the problem of genetic caste conflict and ensured a steady supply of workers. The cost is dependence on maintaining a domesticated lineage of foreign males, a lineage that may degrade over time as harmful mutations accumulate. Yet for now the system has proven successful enough to spread across the Mediterranean, with colonies thriving in regions entirely devoid of natural M. structor populations.
The implications extend to the study of symbiosis, speciation, and the nature of domestication. Whereas human domestication of animals required deliberate selection, M. ibericus achieved something analogous through its own evolutionary trajectory, folding another species into its reproductive system until the two became inseparable. The result is neither pure parasitism nor simple cooperation, but a fusion of lineages that forms an entirely new reproductive unit.
From a broader perspective, this discovery forces scientists to reconsider how species boundaries are defined in eusocial insects. Colonies of M. ibericus cannot be understood as belonging to a single species, because their existence depends on the sustained production of another. Nor can they be considered hybrid swarms, because the queens and reproductive daughters remain true to M. ibericus. Instead, they represent a two-species collective that has evolved stability through cross-species cloning.
The data are comprehensive. Genome sequencing of 390 individuals across five species showed that M. ibericus workers have heterozygosity levels more than fifteen times higher than those of queens, consistent with first-generation hybrids. Mitochondrial analysis confirmed that mothers are always M. ibericus. Nuclear DNA consistently identified M. structor as the paternal species. Laboratory monitoring captured direct evidence of queens producing M. structor males. Sperm dissected from queen spermathecae included both M. ibericus and M. structor. Phylogenetic trees demonstrated a clonal lineage of M. structor males maintained only within M. ibericus nests. The convergence of all these lines of evidence leaves no doubt that xenoparity is real and established.
For evolutionary biology, the case of M. ibericus marks a turning point in understanding how sexual systems can evolve. It shows that reproductive innovation is not limited to incremental shifts but can produce wholly novel arrangements that merge lineages into a single cycle. It also highlights the power of eusociality as a framework for accommodating such innovations, as the colony structure allows the integration of multiple species’ genomes into a functional unit.
For those outside of entomology, the discovery is a reminder that nature still holds reproductive strategies beyond anything humans have imagined. The idea that one mother can create two species simultaneously may seem alien, yet it is happening today in common ants that forage seeds along Mediterranean roadsides. These insects embody a biological paradox: a queen whose daughters require fathers she herself has manufactured from a foreign genome, and a colony that survives only by blurring the lines of species identity.
As scientists continue to monitor these colonies, questions remain about the future of this arrangement. Will the clonal males deteriorate under the weight of accumulating mutations, as some researchers suspect? Can the system sustain itself over millennia, or is it an evolutionary dead end destined for collapse? For now the evidence shows expansion, not decline, with colonies spread across hundreds of sites where M. structor has no presence. In these regions the ants thrive, supported by a reproductive cycle that is unlike any other known in the animal kingdom.
The discovery of xenoparity in Messor ibericus ants represents one of the most bizarre and scientifically significant findings of recent decades. It documents a case where a female must produce another species as part of her own life cycle, creating a two-species superorganism that redefines the concept of reproduction and individuality. What began as a study of harvester ant genetics has revealed an evolutionary system that defies long-standing rules, forces a reevaluation of species boundaries, and demonstrates once again that the natural world contains forms of life stranger than anything imagined in theory.
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Juvé, Y., Lutrat, C., Ha, A., Weyna, A., Lauroua, E., Afonso Silva, A. C., et al. (2025). One mother for two species via obligate cross-species cloning in ants. Nature. https://doi.org/10.1038/s41586-025-09425-w
