Common name: Helm’s stag beetle
Order: Coleoptera Family: Lucanidae
Size: Up to 42mm long
Stag beetles occur throughout the world although our species tend to be less showy than those from overseas. Like other stag beetles, the mandibles (jaws) of male adults are enlarged although not to the same extremes as other exotic species. The adults also tend to spend their days hiding under logs and rocks, emerging only at night or on particularly grey and rainy days.
G. helmsi is the most widespread of the Geodorcus species, occurring along the west coast of the South Island and on offshore islands. The larvae live and feed in soil (which is often enriched by seabird guano on offshore islands). The adults on the other hand have been found feeding on sap oozing out of tree trunks.
Like other ground dwelling insects, stag beetles are vulnerable to predation by small vertebrates like rats. As a result, many of our stag beetles tend to grow to their largest sizes when they live on rat-free islands. One of our most endangered species is the Mokohinau stag beetle (Dorcus ithaginis) which now only exist on a small “room-sized” stack in the Mokohinau Islands.
Endangered species foundation. Ten most endangered species. Retrieved from http://www.endangeredspecies.org.nz/projects/10-most-endangered/
Holloway, B., Jacob, Hēni, & Manaaki Whenua-Landcare Research New Zealand Ltd. (2007). Lucanidae (Insecta:Coleoptera) (Fauna of New Zealand ; no. 61). Lincoln, N.Z.: Manaaki Whenua Press, Landcare Research.