[Topics] Satsuki Kajiwara, a doctoral student at Kyushu University, and colleagues discover aerial "dogfights" in a parasitoid wasp

Females collide with conspecific rivals while hovering to exclude competitors

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Key Points

1. Workers of the host ant Lasius capitatus transport their larvae from tree-trunk nests to underground nests in autumn for overwintering.
2. The parasitoid wasp Ogkosoma cremieri hovers in front of ant nest entrances and oviposits into ant larvae during brief moments when larvae are transported outside the nest.
3. When multiple females of O. cremieri appear simultaneously in front of an ant nest, they engage in intense aerial competition, ramming one another while hovering.

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Abstract

In this study, Satsuki Kajiwara, a first-year doctoral student at the Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, and Associate Professor Takeo Yamauchi of Obihiro University of Agriculture and Veterinary Medicine discovered a remarkable competitive behavior in Ogkosoma cremieri, a parasitoid wasp that attacks ant larvae. When females hover (*1) in front of ant nests while searching for opportunities to oviposit, they engage in intense aerial ramming when rival females appear. This dogfight-like behavior (*2), in which females collide with one another while hovering in midair, is reported for the first time worldwide in parasitoid wasps. Females that were knocked off balance by ramming were observed being attacked by ants and dragged into the nest, indicating that parasitoidic behavior entails substantial risk. Because daytime transport of ant larvae by workers is rare, opportunities for oviposition are limited, which likely leads to intense intraspecific competition among females.

Notably, O. cremieri is relatively large compared with closely related species and possesses broadened and flattened hind-leg segments. These morphological traits may contribute to stable hovering flight and influence the outcomes of aerial contests. This study reveals a previously unknown aspect of parasitoid strategy and provides important insights into the behavioral evolution of parasitoid wasps.

This achievement was published online in Insectes Sociaux, on Saturday, December 13, 2025.

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Fig. 1 Struggle interaction between two female parasitoid wasps (Ogkosoma cremieri). A, two females (yellow and red arrows) hovering in front of an ant nest. B, the female positioned in front of the nest (red arrow) attacked the approaching female (yellow arrow). C, the approaching female (yellow arrow) was pushed away by the female in front of the nest (red arrow). D, the pushed-aside female (yellow arrow) is attacked by ants and dragged into ant nest.

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Glossary

(*1) Hover
to stay in one place in the air, usually by moving the wings quickly

(*2) Dogfight
an aerial battle between fighter aircraft

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Publication Information

Journal: Insectes Sociaux
Title: Parasitoidic strategy of Ogkosoma cremieri (Hymenoptera: Ichneumonidae: Hybrizontinae) against Lasius capitatus (Hymenoptera: Formicidae)
Authors: Satsuki KAJIWARA & Takeo YAMAUCHI
DOI：https://doi.org/10.1007/s00040-025-01072-8

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For Research-related inquiries

Toshiharu Mita, Associate Professor
Mail： t3mita★agr.kyushu‐u.ac.jp
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