Setting the Scene

Now 250km in to my 1000km charity bike ride; tired, sore and almost at the brow of the last hill of the day, I cycled past a male stag beetle wandering out from the grass verge and heading straight for certain death in the two-way traffic.

‘But I’m so close to the top of the hill and the campsite!’ was my first thought. Somewhat reluctantly, I turned around and edged out to rescue him. This was my first encounter with a stag beetle and I am glad I had the energy to go back.

At the end of my cycle across France, we spent a few days in Basque Country (northern Spain). One morning, Emma spotted another beetle appearing from beneath our parked car. This was my first encounter with a female stag beetle.

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Our Species: Lucanus cervus

After consulting a few dedicated invertebrate and stag beetle Facebook groups, we had a good idea of the species we had found. The species is Lucanus cervus (of which their are four subspecies). Remarkably we had found the only one of several Lucanid (stag beetle) species in Europe that we could also have found in the U.K. Not only that, we had found both a male and a female.

Click to ZOOM in

 

L. cervus is widespread in Europe, but in many European countries the species is red-listed and has undergone population declines. Stag beetles are now extinct in Denmark and Latvia. Back in my home country, England, they are confined to the South East. They are the UK’s largest terrestrial beetle.  There is another species in the UK that can be confused with L. cervus, the lesser stag beetle (Dorcus parallelipipedus). To the untrained eye, both the male and female lesser stag beetle look similar to the female L. cervus.

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Sexual Dimorphism

As you can see from the images, the two individuals we found are quite different from each other. All males and females of a species have differences in their sexual organs, but when other physical differences are apparent, we call this sexual dimorphism. Being sexually dimorphic, the males have enlarged mandibles and are larger overall than the females. Their enlarged mandibles are used in combat with other males. This behavioural function, as well as the physical resemblance to the antlers of male deer, are the reasons for the beetle’s common name and species name (‘cervus’ meaning ‘deer’ in Latin.)

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The Stag Beetle’s Life-cycle

Stag beetle females lay their eggs in decaying wood in which their larvae then live within and feed upon. The majority of a stag beetle’s life is spent as a larva underground. In some instances, larvae can remain in the ground for 7 year before leaving the soil, building a cocoon, and then metamorphosing and pupating into an adult beetle. Once an adult, their mission is to find a mate. For an adult stag beetle, time is of the essence as it can be as little as a few weeks or months before they die.

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Factors Affecting Stag Beetle Populations

In many places, stag beetles are struggling due to a variety of factors. These include:

• A significant loss in woodland habitat, as well as the ‘tidying up’ of woodland, parks and gardens. Tree stump grinding and the removal of rotten wood have an impact on stag beetle populations as these refugia are an important place for the female to lay her eggs, and for the young grubs to feed on).
• Changes in weather patterns due to global warming, in the form of extremes in very wet, windy or dry conditions, are also likely to be having negative impacts.
• Stag beetles are attracted to warm surfaces like tarmac and are therefore at risk of being crushed by cars.
• The public seem to have a media-fuelled desire to kill or crush any insect, presumably because they look strange. Although stag beetle males look intimidating with their oversized mandibles, they are most definitely not. The males wrestle other beetles with these. The females are more likely to have a bite at a human handler.

L. cervus is classed as a ‘protected species’ in the UK, listed on Schedule 5 of the Wildlife and Countryside Act 1981. They are also legally protected from sale in the UK.

If you come across a stag beetle, it would be great if you could record your sighting here and leave him or her well be, as long as he/she isn’t in direct danger of being crushed by foot or wheel. If you have to move them, please do so only a short distance. Finally, if you are a woodland manager, part of a local council, or garden owner, you can really help out these magnificent creatures by leaving some wood where it falls, or by building log piles with the help of this instruction sheet.

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Want to Read More?

To read about our encounters with day-flying moths in Spain, check out our blog posts:
Sphingids of Spain: Is That a Hummingbird? No, It’s a Hawk-moth! and
Sphingids of Spain: The Broad-bordered Bee Hawk-moth

To read our other Spanish adventure involving rivers and lizards, click here:
Common Wall Lizards Basking in Basque Country

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References and Further Reading

Buglife Website – Policy and Legislation Summary – https://www.buglife.org.uk/sites/default/files/Policy%20and%20legislation%20summary%20final%202014_0.pdf
(Retrieved 18 August, 2017)

European Stag Beetle Monitoring Network Website – https://www.stagbeetlemonitoring.org/stag-beetles/other-lucanus-species-in-europe/
(Retrieved 18 August, 2017)

Facebook group, Insects of Britain and Northern Europe – https://www.facebook.com/groups/invertid/?fref=nf
(Retrieved 18 August, 2017)

Facebook group, Stag Beetle Conservation Society (no trading) – https://www.facebook.com/groups/24582440395/
(Retrieved 18 August, 2017)

Joint Nature Conservation Committee Website – http://jncc.defra.gov.uk/protectedsites/sacselection/species.asp?FeatureIntCode=S1083
(Retrieved 18 August, 2017)

People’s Trust for Endangered Species Website – https://ptes.org/campaigns/stag-beetles/stag-beetle-facts/
(Retrieved 18 August, 2017)

Wikipedia Website – https://en.wikipedia.org/wiki/Lucanus_cervus
(Retrieved 18 August, 2017)