Ants are social insects and typically form colonies with queens, workers and short-lived males. But a rare species of ant in Japan does things differently: Temnothorax kinomurai has neither males nor workers; this ant species only consists of queens. To raise them, the queens of this species raid nests of a related species, killing its queen and some workers. They then lay their eggs in the foreign nest and have their offspring raised by the workers of the conquered colony. Males are also superfluous in Temnothorax kinomurai because the new queens arise from unfertilized eggs. This way of life is so far unique among ants, as the biologists report.
Ants are one of the most diverse groups of social insects. They have adapted to almost all habitats and play an important role in breaking down organic residues, as mushroom growers or aphid farmers, but also as food for countless birds, arthropods and mammals. Like honey bees and most other social insects, ants often live in colonies with a caste system based on the division of labor: only the queen or queens produce eggs and reproduce. The mostly short-lived males provide their sperm for this purpose, but play no other role. The workers of the ant colony are all females, but they do not reproduce themselves. Instead, they look after the offspring, bring in food and take care of other work that needs to be done in the nest.
Conquered and exploited
However, there are some exceptions to this basic pattern among the approximately 15,700 species of ants: “Some parasitic ant species have lost the worker caste – in these cases the queen penetrates the nests of other species and lets the workers there work for her,” explains senior author Jürgen Heinze from the University of Regensburg. “There are also a few species in which female animals can raise new females from unfertilized eggs without mating through virgin production – the so-called parthenogenesis.” But as Heinze, lead author Keiko Hamaguchi from the Kansai Research Center and their colleagues discovered, there is a species of ant that goes one step further. Temnothorax kinomurai is a very rare species that builds its nests in acorns and has only been found in nine locations in Japan.
This species was already known to attack the nests and workers of other ant species and use them for their own purposes. “Young queens of Temnothorax kinomurai conquer the small nests of the related species Temnothorax makora and kill the queen and some workers by stinging them,” the researchers report. “Then they raise their own offspring with the help of the surviving workers.” However, it was previously unclear whether these offspring actually only included new queens or whether they also included workers or males. To check this, Hamaguchi and her colleagues collected six colonies of Temnothorax kinomurai along with their eggs and larvae and kept them in special nest boxes in the laboratory. After all the young animals had grown, they were able to determine which caste or gender they belonged to.
A species of ants made up only of queens
It turned out that the Temnothorax kinomurai queens actually only produce unfertilized eggs, from which queens later grow again. However, there are no males or workers. This makes this species of ant unique: it is the first known species that completely dispenses with males and workers – and consists only of queens. “The lifestyle of Temnothorax kinomurai is characterized by the unique combination of worker-less parasitism and parthenogenesis, in which female offspring arise from unfertilized eggs,” write Hamaguchi and her colleagues. This underlines the diversity and adaptability of the colony structure of ants and represents a further step in the evolution of parasitic ants. Because they completely forego investing in males or workers and instead invest all available resources in the rearing of parthenogenetic young queens. “This is an unexpected step, but from an evolutionary perspective it makes sense,” says Heinze.
Source: Keiko Hamaguchi (Kansai Research Center, Kyoto) et al., Current Biology, doi: 10.1016/j.cub.2025.11.080