Details
Trypoxylus dichotomus
A beetle renowned for the large, pitchfork-shaped horn that crowns the male's head. In summer it gathers at the oozing sap of oak trees, where rival males joust horn-to-horn for the best feeding spots. It is one of the most beloved insects in Japan.
Map: Ecoregions 2017 © RESOLVE (CC BY 4.0) · Natural Earth (PD)
It ranges across East Asia, from Honshu, Shikoku and Kyushu in Japan through the Korean Peninsula, China and Taiwan. It favours broad-leaved deciduous woodland in lowland hills and low mountains.
Body length runs roughly 3 to 8 cm, with the largest horned males reaching the upper end of that range. Coloration varies from reddish-brown to near-black. Only males carry horns on the head and thorax; the cephalic horn forks into a Y at its tip and bears several points in big individuals. Females lack horns.
It is nocturnal, becoming active at dusk and settling to rest at sunrise. Largely solitary, beetles nonetheless converge on sap-rich trees, where males shove with their horns and try to flip rivals off the feeding site.
Adults feed mainly on the sap that seeps from wounded oaks such as sawtooth and konara oak, and will also lap ripe fruit. The larvae grow on humus and leaf mould in the soil, ignoring living wood and undecayed deadwood.
A female lays about 20 to 30 eggs in the soil, occasionally up to 50. The larvae pass through three instars, with the third instar burrowing deep to overwinter; they pupate the following early summer, so adults emerge roughly one year after the eggs are laid.
A fixture of the Japanese summer, it has been sold commercially since the 1970s and remains a hugely popular pet insect. Once collected mainly from the wild, it is now widely captive-bred and is a classic subject for children's summer nature studies.
