Apterocyclus honoluluensis

Native

Common name(s)

Hawaiian stag beetle

Taxonomy

Family: Lucanidae Subfamily: Lucaninae Genus: Apterocyclus Species: Apterocyclus honoluluensis Waterhouse, 1871

Adult diagnosis

Total body length 14.0–21.0 mm (0.55–0.83 in). Body elongate-oval, thorax constricted anterior to elytra; flight wings lacking. Color dull black. Mandibles falcate; male with variable number of internal teeth; female lacking teeth; surface lacking small tubercles or granulosites in both sexes. Ocular canthus distinct. Front tibia moderately expanded toward apex; external margin with a single, apical tooth, variable number of small external teeth; apical spur projecting forward.

Larval diagnosis

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.

Native range

Kauai. Despite the misleading name, this species is known only from the Kōke’e State Park (Paulsen and Hawks, 2014) area of Kauai.

Plant host(s)

Probably none. This species is not known to feed on living plant tissues. However, adults and larvae are known to be closely associated with dead logs of the native Hawaiian koa tree (Acacia koa) (Osborn, 1920; Paulsen and Hawks, 2014).

Life history

Poorly known. This species is associated with native Hawaiian koa (Acacia koa) forests at elevations above 1,200 meters. Here, flightless adults and larvae burrow amongst rotting koa logs (Van Dyke, 1922), with larvae presumably feeding upon the decaying wood and perhaps associated fungus.

Pest potential

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.

Status in Hawaii

Native, rare, and local. Known only from Kauai. While the stag beetle is now rarely encountered, it appears that it was once much more abundant across its small range (Van Dyke, 1922; Hawaiian Entomological Society, 1915). The decline of the native Hawaiian stag beetles is likely due to a combination of habitat loss and heavy predation from non-native rodent species (Howden, 2008).

Status in Guam

Not established or recorded. There are no records of this species from Guam.

Potential distribution and dispersal pathway

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.

Similar species

Apterocyclus honoluluensis is one of five Apterocyclus known from Kauai. It can be separated from other native stag beetles by examination of the male mandibles (A. honoluluensis with short, falcate mandibles; surface lacking small tubercles or granulosites versus A. palmatus with tusk-like mandibles, A. kawaii with mandibles short, falcate; surface with numerous small tubercles or granulosites), ocular canthus (A. honoluluensis with distinct ocular canthus versus all other Apterocyclus species with canthus indistinct), and front tibia (A. honoluluensis tibia moderately expanded toward apex; external margin with a single, apical tooth, variable number of small external teeth; apical spur projecting forward versus 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, 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. 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 enlarged from base; apical tooth small or lacking, numerous small external teeth; apical spur small and projecting forward).

Other names (synonyms)

Apterocyclus deceptor Sharp, Apterocyclus feminalis Sharp, Apterocyclus varians Sharp

Report your observation

Report your observation of this rare and native Hawaiian species at our iNaturalist project.

Apterocyclus honoluluensis male; photo by E.L. Engasser

Apterocyclus honoluluensis male; photo by E.L. Engasser

Apterocyclus honoluluensis male; photo by E.L. Engasser

Apterocyclus honoluluensis male; photo by E.L. Engasser

Apterocyclus honoluluensis female; photo by E.L. Engasser

Apterocyclus honoluluensis female; photo by E.L. Engasser

Apterocyclus honoluluensis female; photo by E.L. Engasser

Apterocyclus honoluluensis female; photo by E.L. Engasser

Apterocyclus honoluluensis male mandibles; photo by E.L. Engasser

Apterocyclus honoluluensis male mandibles; photo by E.L. Engasser

Apterocyclus honoluluensis male foretibia; photo by E.L. Engasser

Apterocyclus honoluluensis male foretibia; photo by E.L. Engasser

live Apterocyclus larvae found under koa log; photo by M.L. Jameson

live Apterocyclus larvae found under koa log; photo by M.L. Jameson

head view of Apterocylcus larva found under koa log; photo by M.L. Jameson

head view of Apterocylcus larva found under koa log; photo by M.L. Jameson

Acacia koa in bloom; photo by M.L. Jameson

Acacia koa in bloom; photo by M.L. Jameson

distribution map for Apterocyclus honoluluensis

distribution map for Apterocyclus honoluluensis