How to design a predatory firefly? Lessons from the Photurinae (Coleoptera: Lampyridae)

Abstract

Most fireflies (Coleoptera: Lampyridae) do not feed as adults, with the exception of females of some species of the Photurinae subfamily, which are specialists in preying on other fireflies. Even though famous for their predatory behaviour, little is known about the morphology of the photurine fireflies, and how it relates to their predatory behaviour. Females of Nearctic Photuris Dejean, 1833 species are known to readily prey on other fireflies using a diverse behavioral repertoire, which has not been seen in males. Although such sex-specific behaviour is expected to lead to morphological differences, sexual dimorphism has not been investigated in detail in any species of this subfamily. Therefore, the goals of this work were twofold: (i) report for the first time the predatory behaviour of a South American species, Photuris femoralis Curtis, 1839, and review its taxonomy; and (ii) correlate the form of typical photurine features and their function during predation, based on field and cage observations of P. femoralis. Females, but not males, readily preyed on Macrolampis Motschulsky 1853, Amydetes Illiger, 1807 and Aspisoma Laporte, 1833 species. We found that three major features typical of the photurine (observed in 21 species spp. belonging to three genera) are directly involved in predation in P. femoralis: (i) the well developed mandibles and clypeal teeth (greater in females) are used in chewing and piercing the prey; (ii) the strong and flexible legs (including robust, elongated coxa and femora, enlarged trochanters, a loose trochanter-femoral joint, and toothed claws) facilitate prey handling on ground, and also may help catching prey on flight; and (iii) an overall fusiform – less flattened – body shape may increase aerodynamics. The fact that typical photurine features are directly involved in predation suggest that these architectural departures from the ancestral lampyrid body plan may have played a role during the evolution of the typical predatory behavior of the Photurinae.