EUCNEMIDAE  Latreille, 1834  Melasidae Leach, 1817; Eucnemididae Lacordaire, 1857; Perothopidae Lacordaire, 1857; Phylloceridae Reitter, 1905     False Click Beetles, Eucnemid Beetles

Recognition: Eucnemid beetles are immediately distinguished by having a strongly arcuate pronotum that partially or completely hides the head from dorsal view, a hypognathous head, long antennae, proportionately long and slender hind legs, a subcylindrical body, and most species have deep grooves on or associated with the hypomeron for retraction of the antennae.

Habitus: Body elongate, narrow, shallowly to strongly convex; length approximately 2-19 mm; color usually brown to black, occasionally with red or yellow markings; vestiture sparse and short, or finely textured to moderately dense and longer. Head hypognathous, narrower than prothorax, deeply inserted into prothorax. Eyes large, bulging, coarsely faceted. Antenna 11-segmented, often sexually dimorphic, submoniliform or filiform to strongly serrate (female) to pectinate (male); insertions close on frons, giving a triangular form to the frons, distant from eyes; 1st segment long, flagellar attachment eccentric; 2nd segment small. Frons lacking distinct anterior ridge. Labrum reduced to absent, hidden beneath clypeus when present. Mandibles short, stout, chisel-like, arcuate ectally, acute at apex. Maxilla with palpus 4-segmented, apical segment subsecuriform; labium with mentum small, narrowed anteriorly, palpus 3-segmented, apical segment subsecuriform. Thorax with prothorax compact to mesothorax; pronotum transverse, hind angles moderate in length, lateral margins carinate; prosternum with a broadly rounded chin piece, extended posteriorly behind coxae, with narrow ventral process fitting into mesosternal cavity; hypomeron often with notosternal or lateral antennal recesses; procoxal cavities open posteriorly. Scutellum moderately small, obovate to subtriangular. Mesothorax alate and wings functional; venation variable; radial cell large, elongate; medial field usually with wedge cell; apical field with 0-4 sclerotized patches. Mesosternum short, fused to metasternum; median with deep, narrow cavity to receive prosternal process; mesocoxae widely separated. Elytra entire, rounded at apex; striae simple, punctate to finely grooved; intervals flat to shallowly convex, finely punctured; epipleura broad basally, narrow apically. Metasternum quadrate; metacoxae approximate medially, narrowing laterally, usually laminate and covering trochanteral insertion.Legs free; femur fusiform; tibia slender, spinose; tarsi 5-5-5, segments occasionally with ventral setose pads; claw simple. Abdomen with 5 ventrites, all connate. Male aedeagus trilobed; penis usually simple, attenuate; parameres slender, attenuate, to sagittate or hooked apically, variously setiferous, occasionally fused as a tube around penis. Female gonocoxites dorsoventrally compressed; styli reduced, peg-like; bacculum slender, short to long, narrow to spatulate.

Larvae are lightly to moderately sclerotized with darkly sclerotized highlights; body subcylindrical vermiform to strongly dorsoventrally compressed; sparsely pubescent. Head small, prognathous, reduced, lacking epicranial suture; antenna vestigial or minute and 2-segmented; frons, clypeus, labrum and stemmata absent; mandibles reduced, fused to head capsule, strongly curved outwardly; maxilla and labium strongly reduced. Thorax with legs absent; prothorax, mesothorax, metathorax, and abdominal segments 1-8 strongly dorsoventrally compressed. Tergite 9 short, rounded apically, usually lacking urogomphi, often with tubercules or rugose areas. Tergite 10 small, posteroventral. Spiracles biforous, on mesothorax and abdominal segments 1-8; closing apparatus present.

Ecology: Little is known about eucnemids. Adults are usually captured in malaise traps, light traps, or swept or beaten from foliage and decadent wood in lowland and mid-elevational forested environments.Larvae are associated with dying trees or decaying tree portions, including stumps, logs, snags, branches, etc., and apparently feed on fungi, fungus rotted wood, or slimemold plasmodia. Many eucnemid adults have an ability to "click," apparently much as do species of Elateridae and Throscidae.

Status of the Classification: The taxonomy and phylogeny of Eucnemidae subfamilies and tribes was reassessed by Muona (1993, 1995). Generic revisions and species level studies are severely needed for all groups. Only Horn (1890) previously studied the Costa Rican fauna, but this was an extremely limited review due to a lack of specimens. Recently, the family was more narrowly delimited by removal of Subprotelaterinae and Thylacosterninae to the Elateridae. The phylogenetic position of Eucnemidae is not fully resolved; Calder et al. (1992) and Muona (1993, 1995) discuss various hypotheses.

Diversity and Distribution: There are approximately 1200 described species, worldwide. Blackwelder (1944) listed 11 genera and 14 species from Costa Rica, but numerous undescribed and unreported genera and species are known. Thirty-four (34) genera and 100 species are recorded from Central America (Belize to Panama). Seventy-six (76) species are recorded from Nicaragua and Panama, but not Costa Rica.
 
 

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