An inconsistent scaling relationship between tail length and hindwing area among five species (and one subspecies) of European butterfly (Order: Lepidoptera)

Abstract The function of butterfly hindwing tails, narrow protuberances on the hindwing’s trailing edge, is usually attributed to predator evasion (mimicking the head to divert attacks away from vital body parts), or an aerodynamic function. One way of investigating these alternative hypotheses is to determine how hindwing tail length ( L tail ) scales with body size (hindwing area, A hind ). If evolved to mimic a false head, or for aerodynamic performance, we would expect L tail to scale isometrically with A hind ( L tail ∝ A hind 1/2 ), indicating relative similar mimicry and aerodynamic effects across butterfly sizes. If the anti-predator stimulus was optimised for one signal size, we would expect no relationship between L tail and A hind . Accordingly, here, the scaling relationship between L tail and A hind was determined in six species ( Thecla betulae , Favonius quercus , Lampides boeticus , Iphiclides podalirius , Papilio machaon gorganus and Papilio machaon britannicus ) using measurements from museum specimens. No sex-specific differences in scaling patterns were found, suggesting sexual selection plays no role in driving L tail in the species investigated in this study. The scaling between L tail and A hind differed among species, and implied that in some species L tail is likely the result of size dependent trade-offs, possibly between anti-predator effectiveness and aerodynamic costs, which are, in turn, species specific.