Lucanus formosanus is a stag beetle which is endemic to Taiwan, and grows to a length of . Like other species in the Lucanid family, L. formosanus exhibits distinct sexual dimorphism and subsequent external morphological allometry in males.
The Taiwanese stag beetle, Lucanus formosanus, has a distinctive appearance, measuring . Similar to other members of the Lucanid family, this species exhibits pronounced differences between males and females, as well as corresponding adjustments in its external morphology.