Uncertainty about flying conspecifics causes territorial contests of the Old World swallowtail, Papilio machaon

BACKGROUND: Male-male aerial contests of territorial butterflies are difficult to explain by major contest models based on game theory because of butterflies’ apparent inability to inflict substantial costs on their opponent. As an alternative, the “erroneous courtship hypothesis” was presented. This hypothesis is based on the assumption that territorial butterflies cannot discriminate the sex of flying conspecifics. The hypothesis regards the aerial contest of male butterflies as an inevitable same-sex entanglement in the butterflies’ behavioral sequence. To test the robustness of the hypothesis, we investigated the sex recognition abilities of the Old World swallowtail, Papilio machaon. RESULTS: We presented four types of flapping butterfly specimens (fresh male and female, chemicals-removed male and female) to territorial males. The males touched fresh female specimens and showed typical courtship flight. For the other types of specimens, they rarely showed courtship flight although they approached or touched them. In addition, territorial males reacted longer to fresh males than to fresh females. CONCLUSIONS: The results indicated that although territorial males recognize flying females as sexual partners by sensing their semiochemicals, they cannot identify flying conspecific males, and continue to gather information on them. P. machaon is one of the species whose behavior is most incompatible with the erroneous courtship hypothesis, as its males perform a typical courtship flight to flying females, suggesting the ability of sexing flying conspecifics. Nevertheless, the erroneous courtship hypothesis was not disproved by our results. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12983-019-0324-y) contains supplementary material, which is available to authorized users.