Geodorcus helmsi is a large flightless stag beetle that varies in colour from black to brownish-black.

[4] In larger male specimens, the mandibles are long, slender and strongly arched with a conspicuous tooth near their base.

Adults have a wide altitudinal range, from sea level to 1400 m.[5][6] All Geodorcus species are mainly nocturnal and hide underneath fallen log stones or leaf litter on the forest floor.

[5] 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.

[7] All Geodorcus species are protected under Schedule 7 of The 1953 Wildlife Act, making it illegal to hunt, kill, or possess a specimen.