Epomis

Epomis is a genus of ground beetles (Carabidae). The larvae of this genus are notable for being obligate role reversal predators. Amphibians such as frogs are normally predators of beetles, however Epomis larvae feed exclusively on amphibians. Epomis beetles are often metallic blue or green colored, with a striking yellow-orange rim on the elytra and mostly yellow-colored legs and antennae. They are 15–26 millimetres (0.59–1.02 in) in length. They can be distinguished from the closely related genus Chlaenius by the short (less than three times as long as wide) and triangular labial palps. The larvae reach a body length of up to 20 millimetres (0.79 in), they are white or yellow colored, with black and orange markings. Like many ground beetle larvae they are elongated with two extensions (Urogomphi) at the rear end. They have characteristic double-hooked mandibles. Larvae of the two European species can be distinguished by their color pattern. Epomis larvae hunt in a rare reversal of the usual predator-prey relationship between amphibians and insects. They lure their amphibian predators by making prey-like movements, then evade the predator's attack and disable the predator, often with a bite to the throat or underside. After the attack, the larva stays attached to the amphibian while feeding on it, similarly to external parasites. Adult Epomis beetles are generalist predators but can also feed on amphibians. They sneak up behind their victims, and hold on firmly using their legs. To paralyze the victim, the beetle makes an incision in the pelvic region with its mandibles. There is speculation that the incision cuts leg muscles. The amphibian loses its ability to move and is eaten by the beetle. Scientists speculate that Epomis evolved this behavior as an aggressive evasion tactic in response to predation by amphibians and the success of this tactic led to Epomis becoming an obligate predator itself. The genus Epomis belongs to tribe Chlaeniini in the subfamily Licininae, which consists of species associated with swamps, temporary ponds and similar types of wetland habitats. It contains about 30 species distributed in the old world only, with the majority of species occurring in the Afrotropical region. Many taxonomists consider Epomis as a subgenus of Chlaenius, however differences in larval and adult morphology, as well as the unique life history of Epomis beetles, support their separate standing as a genus.