Giant stag beetle: The 'black diamond' of the woods

The giant stag beetle is the king of Japan's stag beetles and a favourite of insect collectors. Shiny and powerful, the males carry great curved mandibles, earning them the nickname "black diamonds" of the insect world. Let's meet this beetle aristocrat of the forest.

Its body

A male giant stag beetle's mandibles are astonishingly large, often longer than half its body. Look closely and you will see a row of teeth on the inside of the jaws — and the shape and number of those teeth can even help tell where the beetle came from. The female's jaws are far smaller; her main job is to slip into rotten wood and lay eggs.

It is a classic "night-living, sap-drinking" beetle: the adults hide in tree crevices by day and gather at night at sap flows on oaks, feeding and sometimes testing their strength against one another.

Where it lives and what it eats

The larvae feed on rotten hardwood and live inside dead trunks for two or three years, growing and moulting until at last they pupate and emerge as a glossy adult. Their whole life is bound to old trees, so an ageing, rotting trunk is their home. That is why keeping old trees and dead wood matters so much to them.

A note for grown-ups

You could talk with a child about how those big jaws are not for biting people: a stag beetle's mandibles are for males wrestling over territory and sap. Realising that an animal's impressive weapon is really for a different purpose is one of the most enjoyable parts of watching nature.