Subgenus of beetles
Epomis is a subgenus of ground beetle genus "Chlaenius". The larvae of this subgenus are notable for being obligate role-reversal predators. Amphibians such as frogs are normally predators of beetles; however, "Epomis" larvae feed exclusively on amphibians.
Description.
"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 in length. Members of the "Epomis" subgenus can be distinguished from other species of "Chlaenius" by the short (less than three times as long as wide) and triangular labial palps.
The larvae reach a body length up to , 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 patterns.
Feeding behavior.
"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. The incision apparently 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.
Taxonomic status.
The subgenus "Epomis" belongs to the genus "Chlaenius" of the tribe Chlaeniini, 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. "Epomis" was formerly considered a genus of the tribe Chlaeniini rather than a subgenus of "Chlaenius".
Species.
These 28 species belong to the subgenus "Epomis":
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References.
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