Hawaiian stag beetle
Family: Lucanidae Subfamily: Lucaninae Genus: Apterocyclus Species: Apterocyclus palmatus Van Dyke, 1921
Only male specimens known (Paulsen and Hawks, 2014). Total body length 22.0–23.0 mm (0.86–0.90 in). Body elongate-oval, thorax constricted anterior to elytra; flight wings lacking. Color dull black. Mandibles elongate, tusk-like; lacking internal teeth; surface lacking small tubercles or granulosites. Ocular canthus indistinct. Front tibia greatly expanded at apex with 1 large apical tooth and 1 large external tooth; apical spur enlarged and projecting medially.
Undescribed. For Lucaninae (Ritcher, 1966): Grub C-shaped, not hump-backed, cylindrical, whitish. Mandible with a ventral process; left molar with inner margin distad of the molar areas with one or more teeth. Maxillary stridulatory teeth usually absent. Maxillary palpus 4-segmented. Thoracic spiracles with emarginations of respiratory plates facing anteriorly. Legs not reduced in size; stridulatory organs present on front and middle legs. Middle leg with trochanter with a stridulatory area consisting of a single longitudinal row of very short transverse ridges. Raster with 2 patches of spine-like setae.
Kauai. Distribution data for this species is particularly scarce. The limited information available from museum specimens indicates that it occurs only on Kauai above elevations of 1,200 m (4,000 ft) (Paulsen and Hawks, 2014).
Probably none. This species is not known to feed on living plant tissues. However, larvae of related Apterocyclus are known to be closely associated with dead logs of the native Hawaiian koa tree (Acacia koa) (Osborn, 1920; Paulsen and Hawks, 2014).
Poorly known. Related Apterocyclus species are associated with native Hawaiian koa (Acacia koa) forests at high elevations. Here, adults and larvae burrow amongst rotting koa logs (Van Dyke, 1922), and larvae presumably feed upon decaying wood and perhaps fungus associated with koa logs.
None. Apterocyclus species are not known to feed on living plants. This, combined with their great rarity and dependence on undisturbed native habitat, greatly limits any pest potential.
Native (possibly extinct). Known only from Kauai. This species has not been collected or recorded in the last 50 years (Paulsen and Hawks, 2014). Like other native Apterocylcus stag beetles, this species has likely suffered from a combination of habitat loss and heavy predation from non-native rodent species (Howden, 2008).
Not established or recorded. There are no records of this species from Guam.
All Apterocyclus species are flightless, rare, and dependent upon vanishing native Hawaiian habitat. As such, members of this genus are unlikely to spread beyond their small natural ranges.
Apterocyclus palmatus is one of five Apterocyclus known from Kauai. It is separated from other native stag beetles by examination of the male mandibles (A. palmatus male with tusk-like mandibles versus mandibles short and falcate in all other Apterocyclus species), ocular canthus (A. palmatus with ocular canthus indistinct versus A. honoluluensis with distinct ocular canthus), and front tibia (A. palmatus with front tibia expanded toward apex with apical ¼ greatly produced; with 1 large apical tooth and 1 large external tooth; apical spur enlarged and projecting medially versus A. kawaii with front tibia gradually expanded toward a greatly broadened apex; with 1 broad apical tooth and 1 weak external tooth; apical spur peg-like, A. honoluluensis with front tibia moderately expanded toward apex; external margin with a single, apical tooth, variable number of small external teeth; apical spur projecting forward, A. munroi tibia moderately expanded toward apex; external margin with 2 teeth at apex (appearing somewhat bidentate); with 2-5 small external teeth; apical spur thin and projecting forward, A. waterhousei with front tibia expanded from base; apical tooth small or lacking, numerous small external teeth; apical spur small and projecting forward).
Apterocyclus honoluluensis var. palmatus Van Dyke
Images temporarily unavailable, see:
Paulsen M, Hawks D. 2014. A review of the primary types of the Hawaiian stag beetle genus Apterocyclus Waterhouse (Coleoptera, Lucanidae, Lucaninae), with the description of a new species. ZooKeys 433: 77–88. doi: 10.3897/zookeys.433.8022
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