Uncover the secret life of stag beetles: these majestic insects reveal a fascinating tale of survival and adaptation
Wildlife researcher and author, Adele Brand, relishes the sight of the iconic stag beetle and offers insights into their intriguing lifecycle and behaviour
On a summer’s evening when the air is so warm that you could cut it with a knife, a whirr, whirr like a rusty old fan signals that our mightiest beetle is on the move.
So alien, so shiny and memorising, it is a wonder that stag beetles are named after the male’s antler-like mandibles rather than, say, a dinosaur or a faraway planet. Their wings beat in the apparent miracle of keeping their chunky three-inch body in flight, and dogwalkers and children playing football look round in amazement.
How to identify stag beetles
Male stag beetles boast impressive antler-like mandibles, ranging from 3.5 to 8cm in length. Males take to the air on balmy summer evenings, seeking out potential mates amidst the twilight glow.
Conversely, female stag beetles possess diminutive jaws and a more modest size, typically measuring between 3 to 5cm in length. Often found foraging on the ground, they diligently search for suitable locations to deposit their precious eggs, ensuring the continuation of their species.
Where do stag beetles live?
That is the puzzle of stag beetles; they are very much of the wild world, yet London is amongst their most important strongholds.
They live their lives under the footsteps of millions of people – the huge white larvae spend up to seven years underground, quietly growing while the city is absorbed in its own dramas.
Despite their size, stag beetles are not the easiest species to study. Faced with a subject that is underground as larvae and unpredictable as adults, scientists have innovated by attaching tiny radio trackers to the back of the beetles’ heads. This has shown that they are disinclined to travel far, highlighting one key stag beetle law: habitat must be long-lasting. Stag beetles severely struggle to recolonise sites that they have lost, no matter how carefully the habitat is restored.
So their surviving homes are important. London has no fewer than three sites internationally protected for stag beetles – Epping Forest, Wimbledon and Putney Commons, and Richmond Park.
Their wider British range is the south-eastern triangle between Hampshire and Suffolk, especially where soils are warm and sandy.
What do stag beetles eat?
Strictly speaking, that question should read, What do stag beetle larvae eat, because once they reach adulthood, stag beetles lose the ability to eat.
The answer to the question is that the larvae feed on rotting wood – they seek decaying stumps weakened by fungi in ancient woodlands, and fence posts, woodchips and even railway sleepers in suburbia.
Throughout their brief adult lifespan of a few weeks, they depend on the fat stores accumulated during their larval phase, and employ their delicate, feathery tongue to extract moisture and glean energy from decaying soft fruits and oozing sap.
Do stag beetles bite?
Despite the intimidating appearance of male stag beetles’ formidable jaws, they are primarily used for grappling with other males in competition for mates rather than for biting.
Females, while theoretically capable of pinching if handled, seldom resort to such behavior.
As always when it comes to wildilfe, it’s advisable to refrain from handling them and allow them to go about their natural activities undisturbed.
When do stag beetles come out?
Come winter, come summer, the larvae are still down there eating, growing, pupating. But eventually, on a warm day in late May, the adult beetle emerges and will continue to do so until August.
The male appears first, perhaps because he pupates at a shallower depth. His ‘antlers’ sweep forward from his head like a Greek laurel, complicating his aerodynamics but preparing him for the battles that await.
Male stag beetles jostle and wrestle like red deer, attempting to knock each other off balance with martial arts-style body lifts. This is for mating rights of course, and the end point is the female laying up to 30 new eggs in rotting wood.
How many stag beetles are left in the UK?
As numbers are currently unknown, why not help scientists find out? You can become a citizen scientist by joining the European stag beetle monitoring network.
Also, find out how you can help save the stag beetle by making a log pile in your garden.
Are stag beetles endangered?
They are a priority species for conservation in the UK due to the gradual shrinking of their habitat range and ongoing habitat loss. Although their population seems relatively stable presently, they face decline across Europe, and have already become extinct in Denmark and Latvia already.
Find out more
Check out our comprehensive expert guide to British beetles, how to make your garden insect friendly and a British insect guide.