''Geodorcus helmsi'', known as New Zealand giant stag beetle or Helms's stag beetle, is a large, slow-moving, flightless
stag beetle
Stag beetles are a family of about 1,200 species of beetles in the family Lucanidae, currently classified in four subfamilies.Smith, A.B.T. (2006). A review of the family-group names for the superfamily Scarabaeoidea (Coleoptera) with corrections ...
in the family Lucanidae. It is
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
to
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
.
Description
''Geodorcus helmsi'' varies in colour from black to brownish-black. Its dorsal surface can vary from dull to glossy. Like other stag beetles, they show
sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
: males range in size from 17.5–44.0 mm, including their large mandibles, while females are smaller (16.5–27.5 mm) with less conspicuous mandibles. In larger male specimens, the mandibles are long, slender and strongly arched with a conspicuous tooth near their base. ''G. helmsi'' is distinguished from other ''Geodorcus'' by its straight un-arched tibiae, and five setose ridges on the
elytra.
Distribution
''Geodorcus helmsi'' is the most widespread of the ten ''Geodorcus'' species, having been collected from
Karamea
Karamea is a town on the West Coast of the South Island of New Zealand. It is the northernmost settlement of any real size on the West Coast, and is located northeast by road from Westport. Apart from a narrow coastal strip, the town of Karam ...
on the northern
West Coast West Coast or west coast may refer to:
Geography Australia
* Western Australia
*Regions of South Australia#Weather forecasting, West Coast of South Australia
* West Coast, Tasmania
**West Coast Range, mountain range in the region
Canada
* Britis ...
of
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
to the south of the
South Island
The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...
, as far as
Tapanui
Tapanui is a small town in West Otago in New Zealand's South Island, close to the boundary with Southland region.
It is a forestry town at the foot of the Blue Mountains and the Pomahaka River. Popular pastimes include deer stalking and trout ...
in
West Otago
West or Occident is one of the four cardinal directions or points of the compass. It is the opposite direction from east and is the direction in which the Sun sets on the Earth.
Etymology
The word "west" is a Germanic word passed into some R ...
. It has also been collected from islands in
Fiordland and from
Stewart Island
Stewart Island ( mi, Rakiura, ' glowing skies', officially Stewart Island / Rakiura) is New Zealand's third-largest island, located south of the South Island, across the Foveaux Strait. It is a roughly triangular island with a total land ar ...
. Adults have a wide altitudinal range, from sea level to 1400 m.
Habitat
All ''Geodorcus'' species are mainly nocturnal and hide underneath fallen log stones or leaf litter on the forest floor.
At night ''D. helmsi'' have been seen active on tree trunks, chewing at the bark to get access to the exudate. This species occupies a highly variable habitat, including forest and tussock-dominated high country.
Diet
The feeding ecology of adult ''G. helmsi'' may be highly variable: they occupy a wide range of habitats from forest to the tussock zone in the high country. Adults have been observed on tree trunks feeding on sappy exudate from wounds in the bark.
Larvae of other lucanid beetles commonly eat the surface of rotting wood. ''Geodorcus'' larvae have been observed to have large quantities of humus inside their gut.
Life cycle
In New Zealand stag beetles, there is no published information about the duration or timing of oviposition, larval, pupal and adult stages of the life cycle. Copulation has been observed in October.
Larvae of ''Geodorcus'' have been seen under decaying logs, occupying a gallery in the soil layer. They are C-shaped, slow moving, and avoid the light.
Conservation
All ''Geodorcus'' species are protected under Schedule 7 of
The 1953 Wildlife Act, making it illegal to hunt, kill, or possess a specimen.
Predation by introduced rats has reduced the population density of ''G. helmsi; o''n islands where rats are present, only their remains can be found.
This species has been found to make up to 27% of the dry weight of feral pig stomach contents.
References
External links
* ''Geodorcus helmsi'' discussed on
RNZ
Radio New Zealand ( mi, Te Reo Irirangi o Aotearoa), commonly known as Radio NZ or simply RNZ, is a New Zealand public-service radio broadcaster and Crown entity that was established under the Radio New Zealand Act 1995. It operates news and cu ...
''
Critter of the Week''
31 May 2019
{{Taxonbar, from=Q2356072
Lucaninae
Beetles of New Zealand
Endemic fauna of New Zealand
Beetles described in 1881
Endemic insects of New Zealand