Invertebrates
European Stag Beetle
Lucanus cervus · also called European stag beetle, greater stag beetle
The European stag beetle is Britain’s largest beetle and one of Europe’s most spectacular — a glossy chestnut-and-black insect whose males carry a pair of jaws shaped exactly like a stag’s antlers, used to wrestle each other on summer evenings. Almost its entire life, though, is spent as a fat white grub in a rotting log.
Overview
European stag beetles live in broadleaf woodland, wood pasture, hedgerows, parks, and gardens with old trees and dead wood, across much of Europe. The adults appear for a few weeks in midsummer; males fly heavily and noisily at dusk on warm evenings, searching by scent for females and for the sap runs on oak trunks where beetles gather.
The antlers
The male’s enormously enlarged mandibles — up to half his body length, branched like antlers — are weapons for male-to-male combat only. Rivals rear up, grip, and try to lever or flip each other off a branch. Despite the size, the jaws close only weakly, so fights rarely injure. Females have small but muscular jaws for chewing into rotten wood to lay eggs, and can nip harder than a male.
A long grub, a brief adult
The larva develops in decaying wood — stumps, buried roots, fallen trunks — for 3 to 6 years, growing to thumb size. The adult never feeds on solids; it laps sap and fruit juice with a small furry tongue and lives only weeks, purely to breed.
Status
The European stag beetle is Near Threatened and declining across Europe, lost from several countries. The cause is the removal of dead and decaying wood from managed landscapes, plus development, roads, and predation of adults on hard surfaces. Leaving dead wood in place and building log pyramids are the main ways to help. It is harmless to people and living plants.
European Stag Beetle: common questions
What are the male stag beetle's huge jaws for?
Fighting other males, and almost nothing else. The oversized mandibles — which can be half the length of the beetle's body and are branched like a stag's antlers, hence the name — are used in ritualised contests over females and over prime spots on tree trunks where females gather at sap runs. Two males face off, rear up, and try to get their jaws around the rival's body and lift or throw him off the branch. The loser is dislodged or backs down. For all their size the jaws close only weakly, so the fights rarely cause real injury; they are a test of size, leverage, and persistence. Females, and small ("minor") males with reduced jaws, do not fight this way.
Why does the adult beetle not eat?
The stag beetle does all its feeding and growing as a larva, over several years, storing enough energy to fuel the entire adult stage. The adult emerges in summer with one job — to reproduce — and it has no functional chewing mouthparts for solid food. It can take in liquids — the adult has a small, brush-tipped, tongue-like organ that it uses to lap tree sap oozing from wounds in oaks and other trees, and juice from soft fallen fruit, which keeps it hydrated and gives it a little energy. It then dies within a few weeks. The male, in particular, often does not feed much at all before mating and dying.
Why is the stag beetle declining?
Its larvae depend absolutely on large quantities of dead and decaying broadleaf wood — old stumps, buried roots, fallen trunks, and standing dead trees — in which to develop over their multi-year life. Modern management of woodland, parks, and gardens tends to remove exactly this — fallen and dead wood is cleared away as "untidy" or as a fire or disease risk, old trees are felled, and stumps are ground out. Habitat is also lost outright to development, and adults are killed in large numbers on roads and by cats, birds, and being trodden on when they land on hard surfaces. The species has disappeared from several European countries and is Near Threatened; leaving dead wood in place, and building "stag beetle log pyramids," are the main things people can do to help.
Is a stag beetle dangerous?
No. It has no venom and no sting. A large male's jaws look formidable but close weakly and cannot break skin. A female's jaws are small but muscular and she can give a sharp pinch if picked up and provoked, enough to make you drop her but not to injure you. Stag beetles are not aggressive and will not chase or attack anything; a male on the ground with jaws raised is bluffing. They are entirely harmless to people, pets, and living plants — the larvae eat only wood that is already dead and rotting.