Victoria Tang


A peculiar intraspecific agonistic behavior involving a non-aggressive physical combat is reported between the adult males of Srilankametrus yaleensis (Kovařík et al., 2019) (Scorpionidae: Heterometrinae). The adult males were observed to resort to a ritualized and relatively gentle way for strength demonstration. The combat is characterized by lateral spreading of pedipalps, chelicerae-to-chelicerae collision, and entanglement of metasomal segments. This behavior is hereby considered a form of an intrasexual combat defined as the “arm-span competition”. It is hypothesized to be beneficial for solving territorial and/ or sexual competitions while avoiding unnecessary mortality which could pose adverse impact to the natural populations. Other Heterometrinae species that possess sexually dimorphic, elongate pedipalps in males were also found to display similar behavior. This may account for at least one potential reason for the evolution of such sexual dimorphism. Finally, this study supplements several other agonistic behaviors (intraguild or antipredatory) observed in scorpions, with special attention to the family Scorpionidae. Three basic types of behavior are defined for this family: aggressive response, shielding response, and arm-span competition. These types of behavior may have implications for the evolution of this family.

Additional Files

Supplemental File 1 - S. yaleensis male-male.MP4 (146370 kB)
S. yaleensis male-male

Supplemental File 2 - C. tristis vs. C. madraspatensis.mp4 (1432878 kB)
C. tristis vs. C. madraspatensis