The Harmless Yet Spectacular Stag Beetle

By José Luis Gallego, environmental communicator (@ecogallego)

When farmers work in the fields, insects tend to be among their regular companions, which is why they usually don't pay them much attention let alone get startled. There are, however, exceptions to this rule.


When it comes to very large insects, most people will find their presence intimidating. I'm fairly certain that anyone who has ever seen the protagonist of this blog post has probably been startled, because its appearance is truly unsettling.


This is the stag beetle (Lucanus cervus), the largest of all European beetles.  The males can reach a size of up to ten centimetres in length – in other words, bigger than some birds. But what is the reason for this imposing size? What has pushed these battleships of the bug world to grow to such large proportions? Once again, the answer can be found in evolution.



 Ejemplar de ciervo volante, encima de una corteza de un árbol.

A stag beetle on a piece of bark



The male stag beetle follows an evolutionary strategy that is very common in nature: impressive size as a way of reducing the number of potential enemies among its natural predators, which flee from its imposing presence the way most humans do. This is especially true if the beetle appears in flight, emitting its tell-tale buzzing sound, which is as magnificent as it is alarming.


But in spite of its size and the spectacular, antler-like mandibles sported by the males, it is in fact one of the most harmless beetles found in our fields.


The stag beetle is only active at dusk and can fly short distances around its territory. Most of us are familiar with adult stag beetles, but once they take on their distinctive appearance, they rarely live more than two or three weeks. The larvae, however, can live up to five or six years, and grow to a length of twenty centimetres, before burrowing into the ground and becoming nymphs. Since they feed on decaying wood, this generally happens near old tree stumps or fallen trees.


Although the adults develop in autumn, they usually remain in the ground until summer when they take flight on warm nights, making it easy to spot them in August. They inhabit mature holm oak and oak forests with cropland (especially vineyards) in between, but they can travel considerable distances, lured by the lights of villages and farmhouses.


The existence of this extraordinary coleopteran is threatened, so much so that some experts predict it will most likely go extinct before the end of this century unless urgent measures to protect the species are taken. For this reason, the species is part of a special monitoring and conservation programme, both in Spain and across Europe.


Personally, I've had great luck encountering these animals, which are among my favourites, and I usually come across them almost every summer. A few years ago, I witnessed a fight between two males on a tree stump deep within a holm oak forest in the nature reserve of Serra d'Espadà in the province of Castellón.



Un ciervo volante, encima de una mano humana.

A stag beetle resting on a human hand.



Observing these spectacular beetles – upright, with their mandibles entangled – engaged in miniature gladiatorial combat gave me one of the finest sketches in my field notebook.     


The stag beetle is a true marvel of evolution. It is also one of the best bioindicators of the environmental health of a forest, which means – yet again – that it isn't just about protecting the species because of what it is, but what it represents.



Un ejemplar de ciervo volante encima de una rama de un árbol.

A stag beetle on a tree branch



Protecting the stag beetle and other saproxylic species – which is what entomologists call insects that feed on the wood of fallen trees – is a direct way of conserving our oldest woodlands, making every effort to achieve this goal more than worthwhile.

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