Mizuno, R., Sadahiro, K., Hosokawa, R., Makita, S., Matsumura, H., Lin, C.-C. & Ito, F.

Temporary social parasitism in the ant Strumigenys mutica: colony composition and behavioral interactions with host species Strumigenys solifontis and Strumigenys lewisi

Temporary social parasitism is the most common type among four types of social parasitism and is known from more than 200 ant species. Queens of temporary social parasites invade a host ant colony, kill the host queen, and use the host workers as a workforce during the colony founding stage. In our study, we collected seven mixed colonies consisting of a Strumigenys mutica queen and its host species: Two included a queen of S. mutica and host workers, five included queens and workers of S. mutica and host workers. In contrast, we also found 14 mature pure S. mutica colonies which included a S. mutica queen and S. mutica workers. The pure colonies were extremely large (max. approx. 5000 workers per colony) compared with other species of this genus. Additionally, S. mutica queens had more ovarioles (10 - 17 in total) than those of other Strumigenys species. Associated with this, the abdomen of S. mutica queens were physogastric with developing ovaries. Behavioral observation of two mixed colonies revealed that S. mutica was highly integrated with their host ants. The foragers of captive S. mutica colonies hunted diverse soil arthropods but struggled to catch springtails, unlike congeneric species. The fact that workers collect food and care for brood is in line with temporary social parasitism but not with other types of social parasitism. Therefore, we confirmed that the rare species S. mutica is a temporary social parasite of other Strumigenys species such as S. lewisi and S. solifontis. Overall, we conclude that S. mutica is a temporary social parasite, showing a novel life history compared with other Strumigenys ants. Our study sheds light on how social parasitism can change the life history of an ant.

Open access, licensed under CC BY 4.0. © 2025 The Author(s).

Pyramica, Kydris, host record, colony composition, physogastrism, foraging, life history, Hymenoptera, Formicidae