Sex-biased differences in perceived risk of predation in an aposematic prey

Abstract

Flight initiation distance (FID) and Distance fled (DF) are two common behavioural metrics used to assess how prey perceive threats from predators. Although widely studied in vertebrates, these are poorly measured in invertebrates, and even less in toxic or chemically defended species. We examined FID and DF in the aposematic, sexually dimorphic painted grasshopper, Poekilocerus pictus, in response to an approaching human. Because predation risk can vary between sexes, habitat type, and time of day, we predicted that these factors would influence grasshopper escape behaviours. Females, which are larger and heavier than males, showed shorter FID and DF. Adult females also have shorter forewings than males. These morphological differences help best explain sex-based variation in escape behaviour. Interestingly, we found grasshoppers that did not escape when approached. The probability that a non-escaping individual was female was significantly higher than that of a male. Habitat also influenced escape responses. Grasshoppers in wooded grasslands (dense) were less likely to fly compared to those in open grasslands. Our study shows that even aposematic, chemically defended prey engage in risk-avoidance behaviours to reduce the likelihood of accidental injury or death from larger organisms such as herbivores, and these risks may be sex-biased. © 2026 Elsevier Ltd